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    <title>Journal of Theoretical, Computational and Applied Mechanics - Latest Publications</title>
    <description>Latest articles</description>
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      <title>episciences.org</title>
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    <pubDate>Sun, 08 Mar 2026 07:26:07 +0000</pubDate>
    <generator>episciences.org</generator>
    <link>https://jtcam.episciences.org</link>
    <author>Journal of Theoretical, Computational and Applied Mechanics</author>
    <dc:creator>Journal of Theoretical, Computational and Applied Mechanics</dc:creator>
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    <item>
      <title>Fracture Toughness of Periodic Beam Lattices</title>
      <description><![CDATA[The study tackles the challenge of accurately modeling fracture behavior in beam lattices, which is essential for designing robust architected materials. Our research focuses on evaluating how the lattice's microstructure and material properties affect fracture toughness. We employed finite element simulations based on the Euler-Bernoulli beam theory to investigate crack propagation, using a failure criterion that initiates beam fracture when maximum axial stress exceeds critical strength. Building on observations from these simulations, we developed a multi-phase-field fracture model with Cosserat elasticity to integrate consistent toughness characteristics into a comprehensive framework for lattice design. This model was validated through experimental tests, ensuring a close match between theoretical predictions and physical reality. Our findings reveal that the energy release rate remains relatively stable during crack propagation, underscoring its reliability as a measure of the toughness of periodic lattice structures. We discovered that toughness is predominantly influenced by beam height and material properties such as tensile strength and Young's modulus, while slenderness has minimal impact. Additionally, cracks were observed to preferentially propagate along the lattice's structural directions due to stress localization effects, highlighting the importance of the microstructure in fracture behavior. The implications of this research are significant, suggesting that improved modeling of fracture in lattice structures can enhance material design reliability and optimization. This study bridges the gap between theoretical models and real-world applications, providing valuable insights for the development of advanced materials with tailored fracture properties.]]></description>
      <pubDate>Thu, 05 Mar 2026 08:53:44 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.14812</link>
      <guid>https://doi.org/10.46298/jtcam.14812</guid>
      <author>Molnár, Gergely</author>
      <author>Réthoré, Julien</author>
      <dc:creator>Molnár, Gergely</dc:creator>
      <dc:creator>Réthoré, Julien</dc:creator>
      <content:encoded><![CDATA[The study tackles the challenge of accurately modeling fracture behavior in beam lattices, which is essential for designing robust architected materials. Our research focuses on evaluating how the lattice's microstructure and material properties affect fracture toughness. We employed finite element simulations based on the Euler-Bernoulli beam theory to investigate crack propagation, using a failure criterion that initiates beam fracture when maximum axial stress exceeds critical strength. Building on observations from these simulations, we developed a multi-phase-field fracture model with Cosserat elasticity to integrate consistent toughness characteristics into a comprehensive framework for lattice design. This model was validated through experimental tests, ensuring a close match between theoretical predictions and physical reality. Our findings reveal that the energy release rate remains relatively stable during crack propagation, underscoring its reliability as a measure of the toughness of periodic lattice structures. We discovered that toughness is predominantly influenced by beam height and material properties such as tensile strength and Young's modulus, while slenderness has minimal impact. Additionally, cracks were observed to preferentially propagate along the lattice's structural directions due to stress localization effects, highlighting the importance of the microstructure in fracture behavior. The implications of this research are significant, suggesting that improved modeling of fracture in lattice structures can enhance material design reliability and optimization. This study bridges the gap between theoretical models and real-world applications, providing valuable insights for the development of advanced materials with tailored fracture properties.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>A gradient-enhanced approach for stable finite element approximations of reaction-convection-diffusion problems</title>
      <description><![CDATA[We develop a micromorphic-based approach for finite element stabilization of reaction-convection-diffusion equations, by gradient enhancement of the field of interest via introducing an auxiliary variable. The well-posedness of the coupled-field approach is established, together with an error estimate. Through a set of 1D and 2D numerical examples the high accuracy and enhanced stability of the approach in approximating solutions associated with complex problems is demonstrated, for situations of varying reactivity and convection.]]></description>
      <pubDate>Sat, 04 Oct 2025 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.15788</link>
      <guid>https://doi.org/10.46298/jtcam.15788</guid>
      <author>Firooz, Soheil</author>
      <author>Reddy, B. Daya</author>
      <author>Steinmann, Paul</author>
      <dc:creator>Firooz, Soheil</dc:creator>
      <dc:creator>Reddy, B. Daya</dc:creator>
      <dc:creator>Steinmann, Paul</dc:creator>
      <content:encoded><![CDATA[We develop a micromorphic-based approach for finite element stabilization of reaction-convection-diffusion equations, by gradient enhancement of the field of interest via introducing an auxiliary variable. The well-posedness of the coupled-field approach is established, together with an error estimate. Through a set of 1D and 2D numerical examples the high accuracy and enhanced stability of the approach in approximating solutions associated with complex problems is demonstrated, for situations of varying reactivity and convection.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Expressing general constitutive models in FEniCSx using external operators and algorithmic automatic differentiation</title>
      <description><![CDATA[Many problems in solid mechanics involve general and non-trivial constitutive models that are difficult to express in variational form. Consequently, it can be challenging to define these problems in automated finite element solvers, such as the FEniCS Project, that use domain-specific languages specifically designed for writing variational forms. In this article, we describe a methodology and software framework for FEniCSx / DOLFINx that enables the expression of constitutive models in nearly any general programming language. We demonstrate our approach on two solid mechanics problems; the first is a simple von Mises elastoplastic model with isotropic hardening implemented with Numba, and the second a Mohr-Coulomb elastoplastic model with apex smoothing implemented with JAX. In the latter case we show that by leveraging JAX's algorithmic automatic differentiation transformations we can avoid error-prone manual differentiation of the terms necessary to resolve the constitutive model. We show extensive numerical results, including Taylor remainder testing, that verify the correctness of our implementation. The software framework and fully documented examples are available as supplementary material under the LGPLv3 or later license.]]></description>
      <pubDate>Sun, 21 Sep 2025 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.14449</link>
      <guid>https://doi.org/10.46298/jtcam.14449</guid>
      <author>Latyshev, Andrey</author>
      <author>Bleyer, Jérémy</author>
      <author>Maurini, Corrado</author>
      <author>Hale, Jack, S</author>
      <dc:creator>Latyshev, Andrey</dc:creator>
      <dc:creator>Bleyer, Jérémy</dc:creator>
      <dc:creator>Maurini, Corrado</dc:creator>
      <dc:creator>Hale, Jack, S</dc:creator>
      <content:encoded><![CDATA[Many problems in solid mechanics involve general and non-trivial constitutive models that are difficult to express in variational form. Consequently, it can be challenging to define these problems in automated finite element solvers, such as the FEniCS Project, that use domain-specific languages specifically designed for writing variational forms. In this article, we describe a methodology and software framework for FEniCSx / DOLFINx that enables the expression of constitutive models in nearly any general programming language. We demonstrate our approach on two solid mechanics problems; the first is a simple von Mises elastoplastic model with isotropic hardening implemented with Numba, and the second a Mohr-Coulomb elastoplastic model with apex smoothing implemented with JAX. In the latter case we show that by leveraging JAX's algorithmic automatic differentiation transformations we can avoid error-prone manual differentiation of the terms necessary to resolve the constitutive model. We show extensive numerical results, including Taylor remainder testing, that verify the correctness of our implementation. The software framework and fully documented examples are available as supplementary material under the LGPLv3 or later license.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>On the Moreau–Jean scheme with the Frémond impact law: energy conservation and dissipation properties for elastodynamics with contact, impact and friction</title>
      <description><![CDATA[The objective of this paper is to propose a time integration scheme for nonsmooth mechanical systems involving one-sided contact, impact and Coulomb friction, that respects the principles of discrete-time energy balance with positive dissipation. To obtain energetic consistency in the continuous time model when an impact occurs, we work with an impact law with friction inspired by the work of M. Frémond (Frémond, 1995, 2001, 2002, 2017) which ensures that dissipation is positive, i.e. that the Clausius–Duhem inequality is satisfied for the impulses and the velocity jumps. On this basis, we propose a time integration method based on the Moreau–Jean scheme (Jean and Moreau, 1987; Moreau, 1988) with a discrete version of the Frémond impact law, and show that this method has correct dissipation properties.]]></description>
      <pubDate>Mon, 30 Jun 2025 09:47:19 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.13480</link>
      <guid>https://doi.org/10.46298/jtcam.13480</guid>
      <author>Acary, Vincent</author>
      <author>Collins-Craft, Nicholas, Anton</author>
      <dc:creator>Acary, Vincent</dc:creator>
      <dc:creator>Collins-Craft, Nicholas, Anton</dc:creator>
      <content:encoded><![CDATA[The objective of this paper is to propose a time integration scheme for nonsmooth mechanical systems involving one-sided contact, impact and Coulomb friction, that respects the principles of discrete-time energy balance with positive dissipation. To obtain energetic consistency in the continuous time model when an impact occurs, we work with an impact law with friction inspired by the work of M. Frémond (Frémond, 1995, 2001, 2002, 2017) which ensures that dissipation is positive, i.e. that the Clausius–Duhem inequality is satisfied for the impulses and the velocity jumps. On this basis, we propose a time integration method based on the Moreau–Jean scheme (Jean and Moreau, 1987; Moreau, 1988) with a discrete version of the Frémond impact law, and show that this method has correct dissipation properties.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>How to introduce an initial crack in phase field simulations to accurately predict the linear elastic fracture propagation threshold?</title>
      <description><![CDATA[Variational phase field fracture models are now widely used to simulate crack propagation in structures. A critical aspect of these simulations is the correct determination of the propagation threshold of pre-existing cracks, as it highly relies on how the initial cracks are implemented. While prior studies briefly discuss initial crack implementation techniques, we present here a systematic investigation. Various techniques to introduce initial cracks in phase field fracture simulations are tested, from the crack explicit meshing to the replacement by a fully damaged phase field, including different variants for the boundary conditions. Our focus here is on phase field models aiming to approximate, in the $\Gamma$-convergence limit, Griffith quasi-static propagation in the framework of Linear Elastic Fracture Mechanics. Therefore, a sharp crack model from classic linear elastic fracture mechanics based on Griffith criterion is the reference in this work. To assess the different techniques to introduce initial cracks, we rely on path-following methods to compute the sharp crack and the phase field smeared crack solutions. The underlying idea is that path-following ensures staying at equilibrium at each instant so that any difference between phase field and sharp crack models can be attributed to numerical artifacts. Thus, by comparing the results from both models, we can provide practical recommendations for reliably incorporating initial cracks in phase field fracture simulations. The comparison shows that an improper initial crack implementation often requires the smeared crack to transition to a one-element-wide phase band to adequately represent a displacement jump along a crack. This transition increases the energy required to propagate the crack, leading to a significant overshoot in the force-displacement response. The take-home message is that to predict the propagation threshold accurately and avoid artificial toughening; the crack must be initialized either setting the phase field to its damage state over a one-element-wide band or meshing the crack explicitly as a one-element-wide slit and imposing the fully cracked state on the crack surface.]]></description>
      <pubDate>Sun, 29 Jun 2025 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.15198</link>
      <guid>https://doi.org/10.46298/jtcam.15198</guid>
      <author>Loiseau, Flavien</author>
      <author>Lazarus, Veronique</author>
      <dc:creator>Loiseau, Flavien</dc:creator>
      <dc:creator>Lazarus, Veronique</dc:creator>
      <content:encoded><![CDATA[Variational phase field fracture models are now widely used to simulate crack propagation in structures. A critical aspect of these simulations is the correct determination of the propagation threshold of pre-existing cracks, as it highly relies on how the initial cracks are implemented. While prior studies briefly discuss initial crack implementation techniques, we present here a systematic investigation. Various techniques to introduce initial cracks in phase field fracture simulations are tested, from the crack explicit meshing to the replacement by a fully damaged phase field, including different variants for the boundary conditions. Our focus here is on phase field models aiming to approximate, in the $\Gamma$-convergence limit, Griffith quasi-static propagation in the framework of Linear Elastic Fracture Mechanics. Therefore, a sharp crack model from classic linear elastic fracture mechanics based on Griffith criterion is the reference in this work. To assess the different techniques to introduce initial cracks, we rely on path-following methods to compute the sharp crack and the phase field smeared crack solutions. The underlying idea is that path-following ensures staying at equilibrium at each instant so that any difference between phase field and sharp crack models can be attributed to numerical artifacts. Thus, by comparing the results from both models, we can provide practical recommendations for reliably incorporating initial cracks in phase field fracture simulations. The comparison shows that an improper initial crack implementation often requires the smeared crack to transition to a one-element-wide phase band to adequately represent a displacement jump along a crack. This transition increases the energy required to propagate the crack, leading to a significant overshoot in the force-displacement response. The take-home message is that to predict the propagation threshold accurately and avoid artificial toughening; the crack must be initialized either setting the phase field to its damage state over a one-element-wide band or meshing the crack explicitly as a one-element-wide slit and imposing the fully cracked state on the crack surface.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Comparison between 2D and 3D fiber-matrix debonding simulation for inverse identification of interface fracture properties</title>
      <description><![CDATA[Fiber-matrix debonding in single fiber specimen is studied experimentally and numerically based on the coupled criterion for which various 2D and one 3D configurations are used. Debonding initiation and propagation are mainly due to normal opening stresses in a 3D model whereas shear stresses play a minor role contrary to a 2D front model, i.e. in a plane normal to the fiber main axis. The 3D model enables describing the free surface singularity similarly to a 2D side model, i.e. along the fiber main axis. The latter cannot represent the debonding arrest and stable propagation after initiation. Overall, a 2D front model under plane strain assumption provides the best description of debonding initiation loading level compared to the 3D model, yet for a larger debonding opening. Experimental debonding openings are determined using DIC, providing the debonding initiation remote loading and corresponding opening. Tensile strengths and critical energy release rates respectively slightly higher and in the same order of magnitude are identified in 3D, based on the debonding opening, compared to a 2D front model.]]></description>
      <pubDate>Sun, 29 Jun 2025 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.12997</link>
      <guid>https://doi.org/10.46298/jtcam.12997</guid>
      <author>Girard, Hugo</author>
      <author>Doitrand, Aurélien</author>
      <author>Koohbor, Behrad</author>
      <author>Rinaldi, Renaud, G</author>
      <author>Godin, Nathalie</author>
      <author>Bikard, Jérôme</author>
      <dc:creator>Girard, Hugo</dc:creator>
      <dc:creator>Doitrand, Aurélien</dc:creator>
      <dc:creator>Koohbor, Behrad</dc:creator>
      <dc:creator>Rinaldi, Renaud, G</dc:creator>
      <dc:creator>Godin, Nathalie</dc:creator>
      <dc:creator>Bikard, Jérôme</dc:creator>
      <content:encoded><![CDATA[Fiber-matrix debonding in single fiber specimen is studied experimentally and numerically based on the coupled criterion for which various 2D and one 3D configurations are used. Debonding initiation and propagation are mainly due to normal opening stresses in a 3D model whereas shear stresses play a minor role contrary to a 2D front model, i.e. in a plane normal to the fiber main axis. The 3D model enables describing the free surface singularity similarly to a 2D side model, i.e. along the fiber main axis. The latter cannot represent the debonding arrest and stable propagation after initiation. Overall, a 2D front model under plane strain assumption provides the best description of debonding initiation loading level compared to the 3D model, yet for a larger debonding opening. Experimental debonding openings are determined using DIC, providing the debonding initiation remote loading and corresponding opening. Tensile strengths and critical energy release rates respectively slightly higher and in the same order of magnitude are identified in 3D, based on the debonding opening, compared to a 2D front model.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Normal form analysis of nonlinear oscillator equations with automated arbitrary order expansions</title>
      <description><![CDATA[Arbitrary order expansions for the automatic reduction and solutions of nonlinear vibratory systems have been developed successfully within the realm of the direct parametrisation of invariant manifolds. Whereas the method has been used with high-order expansions and large dimensional systems, this article proposes to look at the same problem from the opposite view angle. By using low-dimensional systems, symbolic computations, analytical developments and numerical verifications, this contribution analyzes the reduced dynamics appearing in cases where a single master mode is involved, reviewing typical scenarios in nonlinear vibrations: primary resonance, sub- and superharmonic resonances and parametric excitation. To achieve this task, the normal form style is preferentially used. A symbolic open-source package is also provided to generalize the presented results to other styles, higher orders, and different scenarios. It is shown how the low-order terms allow recovering the classical solutions given by perturbation methods, and how the automated expansions allow one to generalize the analysis to arbitrary orders. When analytical solutions are not tractable anymore, numerical solutions are employed to underline how converged solutions are at hand when the validity limit of the expansions is not reached. All the results presented in this paper can thus be used to better understand the nonlinear dynamical solutions occurring in nonlinear vibrations, as well as from a system identification perspective, since the normal form is the simplest dynamical system displaying a given resonance scenario.]]></description>
      <pubDate>Mon, 19 May 2025 13:48:02 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.13234</link>
      <guid>https://doi.org/10.46298/jtcam.13234</guid>
      <author>de Figueiredo Stabile, André</author>
      <author>Touzé, Cyril</author>
      <author>Vizzaccaro, Alessandra</author>
      <dc:creator>de Figueiredo Stabile, André</dc:creator>
      <dc:creator>Touzé, Cyril</dc:creator>
      <dc:creator>Vizzaccaro, Alessandra</dc:creator>
      <content:encoded><![CDATA[Arbitrary order expansions for the automatic reduction and solutions of nonlinear vibratory systems have been developed successfully within the realm of the direct parametrisation of invariant manifolds. Whereas the method has been used with high-order expansions and large dimensional systems, this article proposes to look at the same problem from the opposite view angle. By using low-dimensional systems, symbolic computations, analytical developments and numerical verifications, this contribution analyzes the reduced dynamics appearing in cases where a single master mode is involved, reviewing typical scenarios in nonlinear vibrations: primary resonance, sub- and superharmonic resonances and parametric excitation. To achieve this task, the normal form style is preferentially used. A symbolic open-source package is also provided to generalize the presented results to other styles, higher orders, and different scenarios. It is shown how the low-order terms allow recovering the classical solutions given by perturbation methods, and how the automated expansions allow one to generalize the analysis to arbitrary orders. When analytical solutions are not tractable anymore, numerical solutions are employed to underline how converged solutions are at hand when the validity limit of the expansions is not reached. All the results presented in this paper can thus be used to better understand the nonlinear dynamical solutions occurring in nonlinear vibrations, as well as from a system identification perspective, since the normal form is the simplest dynamical system displaying a given resonance scenario.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>A Level Set Discrete Element Model for sintering with an optimization-based contact detection</title>
      <description><![CDATA[Sintering is a high temperature process for the consolidation of ceramic, metal and polymer powders. The Discrete Element Method (DEM) has been effectively used to model the sintering process at the particle scale considering spherical particles. However, standard manufacturing processes rarely deal with spherical particles. As sintering is a curvature-controlled process, it is important to take into account the deviation from sphericity. This study presents a DEM sintering model for non-spherical particles. The description and dynamic evolution of arbitrary shape particles is achieved by using the Level Set discrete element method (LS-DEM). The original LS-DEM approach uses boundary nodes on the particles to detect contacts. We employ an optimization-based contact detection approach. This improves the capture of small contacts, which is important for a correct description of sintering evolution with reasonable CPU-time consumption. A Newton-Raphson scheme is employed for the optimization algorithm. The normal force and neck size evolution expressions of spherical particles are adapted for arbitrary shape particles by using the local curvature at the contact. The developed model is validated for elastic contacts on superquadric ellipsoids. It is compared with standard DEM on spheres for sintering. The model is applied to investigate the consolidation kinetics of a packing of ellipsoidal particles. It is shown, that a deviation from sphericity is beneficial for both prolate and oblate ellipsoids. An optimum aspect ratio is evaluated, demonstrating that particles that are too elongated slow down densification kinetics.]]></description>
      <pubDate>Thu, 24 Apr 2025 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.13721</link>
      <guid>https://doi.org/10.46298/jtcam.13721</guid>
      <author>Paredes-Goyes, Brayan</author>
      <author>Jauffres, David</author>
      <author>Martin, Christophe, L</author>
      <dc:creator>Paredes-Goyes, Brayan</dc:creator>
      <dc:creator>Jauffres, David</dc:creator>
      <dc:creator>Martin, Christophe, L</dc:creator>
      <content:encoded><![CDATA[Sintering is a high temperature process for the consolidation of ceramic, metal and polymer powders. The Discrete Element Method (DEM) has been effectively used to model the sintering process at the particle scale considering spherical particles. However, standard manufacturing processes rarely deal with spherical particles. As sintering is a curvature-controlled process, it is important to take into account the deviation from sphericity. This study presents a DEM sintering model for non-spherical particles. The description and dynamic evolution of arbitrary shape particles is achieved by using the Level Set discrete element method (LS-DEM). The original LS-DEM approach uses boundary nodes on the particles to detect contacts. We employ an optimization-based contact detection approach. This improves the capture of small contacts, which is important for a correct description of sintering evolution with reasonable CPU-time consumption. A Newton-Raphson scheme is employed for the optimization algorithm. The normal force and neck size evolution expressions of spherical particles are adapted for arbitrary shape particles by using the local curvature at the contact. The developed model is validated for elastic contacts on superquadric ellipsoids. It is compared with standard DEM on spheres for sintering. The model is applied to investigate the consolidation kinetics of a packing of ellipsoidal particles. It is shown, that a deviation from sphericity is beneficial for both prolate and oblate ellipsoids. An optimum aspect ratio is evaluated, demonstrating that particles that are too elongated slow down densification kinetics.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Multi-material topology optimization of structural load-bearing capacity using limit analysis</title>
      <description><![CDATA[We extend the problem of finding an optimal structure with maximum load-bearing capacity to the case of multiple materials. We first consider a reinforcement optimization case where the structure consists of a fixed background matrix material with given strength properties and optimize the reinforcement topology within this material. We discuss the use of various isotropic and anisotropic strength criteria to model the reinforcing phase, including reinforcements with discrete orientations. In a second time, we investigate a bi-material formulation where we optimize the topology of two material phases simultaneously. Various choices for the material strength conditions are proposed and we apply this formulation to the optimization of pure tensile and compressive phases of a single material. In all cases, two optimization variants are proposed using concepts of convex optimization and limit analysis theory, namely maximizing the load-bearing capacity under a fixed volume constraint or minimizing the volume under a fixed loading. Both problems are convex and a penalization procedure is proposed. The underlying problems can be solved using conic programming solvers. Illustrative applications demonstrate the versatility of the proposed formulation, including the influence of the selected strength criteria, the possibility to obtain structures with members of fixed orientation or structures with different importance granted to tensile and compressive regions. Finally, we also draw a parallel with the generation of strut-and-tie models for the analysis of reinforced concrete structures.]]></description>
      <pubDate>Thu, 06 Feb 2025 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.12427</link>
      <guid>https://doi.org/10.46298/jtcam.12427</guid>
      <author>Mourad, Leyla</author>
      <author>Bleyer, Jeremy</author>
      <author>Mesnil, Romain</author>
      <author>Nseir, Joanna</author>
      <author>Sab, Karam</author>
      <author>Raphael, Wassim</author>
      <dc:creator>Mourad, Leyla</dc:creator>
      <dc:creator>Bleyer, Jeremy</dc:creator>
      <dc:creator>Mesnil, Romain</dc:creator>
      <dc:creator>Nseir, Joanna</dc:creator>
      <dc:creator>Sab, Karam</dc:creator>
      <dc:creator>Raphael, Wassim</dc:creator>
      <content:encoded><![CDATA[We extend the problem of finding an optimal structure with maximum load-bearing capacity to the case of multiple materials. We first consider a reinforcement optimization case where the structure consists of a fixed background matrix material with given strength properties and optimize the reinforcement topology within this material. We discuss the use of various isotropic and anisotropic strength criteria to model the reinforcing phase, including reinforcements with discrete orientations. In a second time, we investigate a bi-material formulation where we optimize the topology of two material phases simultaneously. Various choices for the material strength conditions are proposed and we apply this formulation to the optimization of pure tensile and compressive phases of a single material. In all cases, two optimization variants are proposed using concepts of convex optimization and limit analysis theory, namely maximizing the load-bearing capacity under a fixed volume constraint or minimizing the volume under a fixed loading. Both problems are convex and a penalization procedure is proposed. The underlying problems can be solved using conic programming solvers. Illustrative applications demonstrate the versatility of the proposed formulation, including the influence of the selected strength criteria, the possibility to obtain structures with members of fixed orientation or structures with different importance granted to tensile and compressive regions. Finally, we also draw a parallel with the generation of strut-and-tie models for the analysis of reinforced concrete structures.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>The Redundancy Matrix as a Performance Indicator for Structural Assessment</title>
      <description><![CDATA[The degree of static indeterminacy and its spatial distribution characterize load-bearing structures independent of a specific load case. The redundancy matrix stores the distribution of the static indeterminacy on its main diagonal, and thereby offers the possibility to use this property for the assessment of structures. It is especially suitable to be used in early planning stages for design exploration. In this paper, performance indicators with respect to robustness and assemblability are derived from the redundancy matrix. For each of the performance indicators, a detailed matrix-based derivation is given and the application is showcased with various truss examples.]]></description>
      <pubDate>Wed, 05 Feb 2025 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.13574</link>
      <guid>https://doi.org/10.46298/jtcam.13574</guid>
      <author>Forster, David</author>
      <author>von Scheven, Malte</author>
      <dc:creator>Forster, David</dc:creator>
      <dc:creator>von Scheven, Malte</dc:creator>
      <content:encoded><![CDATA[The degree of static indeterminacy and its spatial distribution characterize load-bearing structures independent of a specific load case. The redundancy matrix stores the distribution of the static indeterminacy on its main diagonal, and thereby offers the possibility to use this property for the assessment of structures. It is especially suitable to be used in early planning stages for design exploration. In this paper, performance indicators with respect to robustness and assemblability are derived from the redundancy matrix. For each of the performance indicators, a detailed matrix-based derivation is given and the application is showcased with various truss examples.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>On the bifurcation analysis of thin multilayer structures by the Asymptotic Numerical Method</title>
      <description><![CDATA[This paper focuses on the stability analysis of multilayer thin shells using the asymptotic numerical method (ANM) combined with Padé approximants. This technique is highly effective for solving nonlinear problems due to its high-order algorithm that ensures accurate computation of singular points along nonlinear solution branches. We present various methods for detecting bifurcation points. The first technique uses a bifurcation indicator integrated into the nonlinear problem as a scalar function. This function represents the intensity of a fictitious perturbation force, evaluated along the equilibrium branch and vanishing exactly at singular points. The second method employs Padé approximants as a bifurcation indicator by analyzing the denominator of rational fractions. The third method identifies singular points by combining buckling and linear vibrations, examining the evolution of natural frequencies along the equilibrium path. The paper evaluates these three bifurcation detection techniques for multilayer composite structures. It also analyses the impact of the solution representation by power series or Padé approximants, the truncation order, and the accuracy parameter on the solution path.]]></description>
      <pubDate>Tue, 04 Feb 2025 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.10170</link>
      <guid>https://doi.org/10.46298/jtcam.10170</guid>
      <author>Azzayani, Hamza</author>
      <author>Zahrouni, Hamid</author>
      <author>Mathieu, Norman</author>
      <author>Ventura, Pascal</author>
      <author>Brun, Michael</author>
      <author>Potier-Ferry, Michel</author>
      <dc:creator>Azzayani, Hamza</dc:creator>
      <dc:creator>Zahrouni, Hamid</dc:creator>
      <dc:creator>Mathieu, Norman</dc:creator>
      <dc:creator>Ventura, Pascal</dc:creator>
      <dc:creator>Brun, Michael</dc:creator>
      <dc:creator>Potier-Ferry, Michel</dc:creator>
      <content:encoded><![CDATA[This paper focuses on the stability analysis of multilayer thin shells using the asymptotic numerical method (ANM) combined with Padé approximants. This technique is highly effective for solving nonlinear problems due to its high-order algorithm that ensures accurate computation of singular points along nonlinear solution branches. We present various methods for detecting bifurcation points. The first technique uses a bifurcation indicator integrated into the nonlinear problem as a scalar function. This function represents the intensity of a fictitious perturbation force, evaluated along the equilibrium branch and vanishing exactly at singular points. The second method employs Padé approximants as a bifurcation indicator by analyzing the denominator of rational fractions. The third method identifies singular points by combining buckling and linear vibrations, examining the evolution of natural frequencies along the equilibrium path. The paper evaluates these three bifurcation detection techniques for multilayer composite structures. It also analyses the impact of the solution representation by power series or Padé approximants, the truncation order, and the accuracy parameter on the solution path.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>A review of the coupled criterion</title>
      <description><![CDATA[We provide a review of recent works about the Coupled Criterion (CC), originally developed to assess the initiation of a crack and thus overcome a main limitation of linear elastic fracture mechanics. This paper includes theoretical and implementation aspects of the CC, new fundamental developments such as extensions to 3D, dynamic aspects, nonlinearities or fatigue. It also focuses on confrontations between the CC and other fracture modeling approaches such as cohesive zone models or phase field approach for fracture. Originally developed in 2D, for linear elastic materials under the assumption of small deformations, the CC has now expanded and can be applied to a wide range of applications from macroscopic to atomic scale.]]></description>
      <pubDate>Sat, 23 Nov 2024 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.11072</link>
      <guid>https://doi.org/10.46298/jtcam.11072</guid>
      <author>Doitrand, Aurélien</author>
      <author>Duminy, Thomas</author>
      <author>Girard, Hugo</author>
      <author>Chen, Xi</author>
      <dc:creator>Doitrand, Aurélien</dc:creator>
      <dc:creator>Duminy, Thomas</dc:creator>
      <dc:creator>Girard, Hugo</dc:creator>
      <dc:creator>Chen, Xi</dc:creator>
      <content:encoded><![CDATA[We provide a review of recent works about the Coupled Criterion (CC), originally developed to assess the initiation of a crack and thus overcome a main limitation of linear elastic fracture mechanics. This paper includes theoretical and implementation aspects of the CC, new fundamental developments such as extensions to 3D, dynamic aspects, nonlinearities or fatigue. It also focuses on confrontations between the CC and other fracture modeling approaches such as cohesive zone models or phase field approach for fracture. Originally developed in 2D, for linear elastic materials under the assumption of small deformations, the CC has now expanded and can be applied to a wide range of applications from macroscopic to atomic scale.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Deformation and cavitation at the spherulite scale of an isotactic polypropylene</title>
      <description><![CDATA[Engineering stress-strain curves are generated from tensile tests on semi-crystalline thermoplastics, which may exhibit non-linearity and/or peak stress associated with striction/necking phenomenon of the specimen at the macroscopic scale. This work addresses this state of deformed specimen, on an isotactic polypropylene, where irreversible strains have led to a variable cross-sectional area along the necked region. 3D images in this region, obtained through Synchrotron Radiation Computed Tomography with two high resolutions are exploited. The best resolution (1 pixel length = 0.05 μm) allowed better understanding of the morphology of several deformed spherulites within which polar fan arrangements are clearly detailed. Thanks to the dentification of the boundaries of spherulite patterns, with a 0.7 μm resolution, the longitudinal and transverse elongations of larger numbers of spherulites are measured. The evolution of the volumetric plastic strains due to cavitation at the spherulitic scale along the necked regions is comprehensively analysed. Volume changes at this scale are highlighted, consisting of an increase in the case of void growth followed by a decrease at large strains due to the collapse of elongated voids. The effects of these results on the establishment of reliable constitutive model are discussed. It is found that accounting for plastic dilation is necessary for the accuracy of constitutive models.]]></description>
      <pubDate>Wed, 25 Sep 2024 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.11335</link>
      <guid>https://doi.org/10.46298/jtcam.11335</guid>
      <author>Laiarinandrasana, Lucien</author>
      <author>Klinkova, Olga</author>
      <author>Ovalle, Cristian</author>
      <author>Cloetens, Peter</author>
      <author>Proudhon, Henry</author>
      <author>Morgeneyer, Thilo, F.</author>
      <dc:creator>Laiarinandrasana, Lucien</dc:creator>
      <dc:creator>Klinkova, Olga</dc:creator>
      <dc:creator>Ovalle, Cristian</dc:creator>
      <dc:creator>Cloetens, Peter</dc:creator>
      <dc:creator>Proudhon, Henry</dc:creator>
      <dc:creator>Morgeneyer, Thilo, F.</dc:creator>
      <content:encoded><![CDATA[Engineering stress-strain curves are generated from tensile tests on semi-crystalline thermoplastics, which may exhibit non-linearity and/or peak stress associated with striction/necking phenomenon of the specimen at the macroscopic scale. This work addresses this state of deformed specimen, on an isotactic polypropylene, where irreversible strains have led to a variable cross-sectional area along the necked region. 3D images in this region, obtained through Synchrotron Radiation Computed Tomography with two high resolutions are exploited. The best resolution (1 pixel length = 0.05 μm) allowed better understanding of the morphology of several deformed spherulites within which polar fan arrangements are clearly detailed. Thanks to the dentification of the boundaries of spherulite patterns, with a 0.7 μm resolution, the longitudinal and transverse elongations of larger numbers of spherulites are measured. The evolution of the volumetric plastic strains due to cavitation at the spherulitic scale along the necked regions is comprehensively analysed. Volume changes at this scale are highlighted, consisting of an increase in the case of void growth followed by a decrease at large strains due to the collapse of elongated voids. The effects of these results on the establishment of reliable constitutive model are discussed. It is found that accounting for plastic dilation is necessary for the accuracy of constitutive models.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Mesh Density and Geodesic Tortuosity in Planar Triangular Tesselations Devoted to Fracture Mechanics</title>
      <description><![CDATA[In fracture mechanics, the mesh sensitivity is a key issue. It is particularly true concerning cohesive volumetric finite element methods in which the crack path and the overall behavior are respectively influenced by the mesh topology and the mesh density. Poisson-Delaunay tessellations parameters, including the edge length distributions, were widely studied in the literature but very few works concern the mesh density and topology in Delaunay type meshes suitable for finite element simulations, which is of crucial interest for practical use. Starting from previous results concerning Poisson-Delaunay tessellations and studying in detail the Lloyd relaxation algorithm, we propose estimates for the probability density functions of the edge length and triangle top angles sets. These estimates depend both on the intensity of the underlying point process and on an efficiency index associated to the global quality of the mesh. The global and local accuracies of these estimates are checked for various standard mesh generators. Finally the mesh density and geodesic tortuosity are estimated for standard random or structured triangular meshes typically used in finite element simulations. These results provide practical formulas to estimate bias introduced by the mesh density and topology on the results of cohesive-volumetric finite element simulations.]]></description>
      <pubDate>Tue, 24 Sep 2024 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.9768</link>
      <guid>https://doi.org/10.46298/jtcam.9768</guid>
      <author>Lhonneur, Joffrey</author>
      <author>Blal, Nawfal</author>
      <author>Monerie, Yann</author>
      <dc:creator>Lhonneur, Joffrey</dc:creator>
      <dc:creator>Blal, Nawfal</dc:creator>
      <dc:creator>Monerie, Yann</dc:creator>
      <content:encoded><![CDATA[In fracture mechanics, the mesh sensitivity is a key issue. It is particularly true concerning cohesive volumetric finite element methods in which the crack path and the overall behavior are respectively influenced by the mesh topology and the mesh density. Poisson-Delaunay tessellations parameters, including the edge length distributions, were widely studied in the literature but very few works concern the mesh density and topology in Delaunay type meshes suitable for finite element simulations, which is of crucial interest for practical use. Starting from previous results concerning Poisson-Delaunay tessellations and studying in detail the Lloyd relaxation algorithm, we propose estimates for the probability density functions of the edge length and triangle top angles sets. These estimates depend both on the intensity of the underlying point process and on an efficiency index associated to the global quality of the mesh. The global and local accuracies of these estimates are checked for various standard mesh generators. Finally the mesh density and geodesic tortuosity are estimated for standard random or structured triangular meshes typically used in finite element simulations. These results provide practical formulas to estimate bias introduced by the mesh density and topology on the results of cohesive-volumetric finite element simulations.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>An implicit staggered algorithm for CPFEM-based analysis of aluminum</title>
      <description><![CDATA[In this paper, we propose an implicit staggered algorithm for crystal plasticity finite element methodwhich makes use of dynamic relaxation at the constitutive integration level. An uncoupled version ofthe constitutive system consists of a multi-surface flow law complemented by an evolution law for thehardening variables. Since a saturation law is adopted for hardening, a sequence of nonlinear iterationfollowed by a linear system is feasible. To tie the constitutive unknowns, the dynamic relaxation method isadopted. A Green-Nagdhi plasticity model is adopted based on the Hencky strain calculated using a[2/2] Padé approximation. For the incompressible case, the approximation error is calculated exactly.A enhanced-assumed strain element technology is adopted, which was found to be especially suitedto localization problems such as the ones resulting from crystal plasticity plane slipping. Analysis ofthe results shows significant reduction of drift and well defined localization without spurious modes orhourglassing.]]></description>
      <pubDate>Fri, 20 Sep 2024 11:07:44 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.12960</link>
      <guid>https://doi.org/10.46298/jtcam.12960</guid>
      <author>Areias, Pedro</author>
      <author>dos Santos, Charles</author>
      <author>Melicio, Rui</author>
      <author>Silvestre, Nuno</author>
      <dc:creator>Areias, Pedro</dc:creator>
      <dc:creator>dos Santos, Charles</dc:creator>
      <dc:creator>Melicio, Rui</dc:creator>
      <dc:creator>Silvestre, Nuno</dc:creator>
      <content:encoded><![CDATA[In this paper, we propose an implicit staggered algorithm for crystal plasticity finite element methodwhich makes use of dynamic relaxation at the constitutive integration level. An uncoupled version ofthe constitutive system consists of a multi-surface flow law complemented by an evolution law for thehardening variables. Since a saturation law is adopted for hardening, a sequence of nonlinear iterationfollowed by a linear system is feasible. To tie the constitutive unknowns, the dynamic relaxation method isadopted. A Green-Nagdhi plasticity model is adopted based on the Hencky strain calculated using a[2/2] Padé approximation. For the incompressible case, the approximation error is calculated exactly.A enhanced-assumed strain element technology is adopted, which was found to be especially suitedto localization problems such as the ones resulting from crystal plasticity plane slipping. Analysis ofthe results shows significant reduction of drift and well defined localization without spurious modes orhourglassing.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Non-local fatigue criterion based on standard deviation for notches and defects in Ti-6Al-4V</title>
      <description><![CDATA[The aim of this study is to propose a non local multiaxial fatigue criterion in order to assess the fatigue limit of stress concentrator such as notches or defects in Ti-6Al-4V. This criterion is based on the standard deviation of the stresses integrated over a given volume around the hot spot point. Up to now, the standard deviation has never been tested as an indicator of stress heterogeneity to assess fatigue life of notch components. Four parameters are necessary to identify the criterion. The criterion is first validated on notched samples based on literature results and shows very good results. A set of experimental tests is conducted on natural and artificial defects including clustering defects and demonstrates the flexibility and accuracy of the criterion.]]></description>
      <pubDate>Thu, 19 Sep 2024 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.12473</link>
      <guid>https://doi.org/10.46298/jtcam.12473</guid>
      <author>Bodlet, Natan</author>
      <author>Amargier, Rémi</author>
      <author>Nadot, Yves</author>
      <dc:creator>Bodlet, Natan</dc:creator>
      <dc:creator>Amargier, Rémi</dc:creator>
      <dc:creator>Nadot, Yves</dc:creator>
      <content:encoded><![CDATA[The aim of this study is to propose a non local multiaxial fatigue criterion in order to assess the fatigue limit of stress concentrator such as notches or defects in Ti-6Al-4V. This criterion is based on the standard deviation of the stresses integrated over a given volume around the hot spot point. Up to now, the standard deviation has never been tested as an indicator of stress heterogeneity to assess fatigue life of notch components. Four parameters are necessary to identify the criterion. The criterion is first validated on notched samples based on literature results and shows very good results. A set of experimental tests is conducted on natural and artificial defects including clustering defects and demonstrates the flexibility and accuracy of the criterion.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>An explicit dynamics framework suited to highly non-smooth interface behaviors</title>
      <description><![CDATA[Dynamic systems, and in particular mechanical structures, may be subjected to non-smooth loadings such as impacts or shocks. Moreover, their behavior itself may exhibit more or less non-smooth evolutions, as when fracture occurs. Therefore, robust simulation models are of interest to capture such behaviors. A particular focus is made herein on time-stepping explicit dynamics schemes to allow efficient simulations, and non-smoothness is embedded within the discrete resolution model, so that robust simulations can be obtained, with a minimum number of numerical parameters. The original contributions of this article lie in the way the non-smooth behavior is formulated to be embedded in an explicit dynamics framework. This study focuses on the solver for dynamics with non-smooth interface behavior, rather than on the behavior models themselves. The applications concern non-smooth interface behaviors at macroscopic scale, between displacement jump on the 2D interface surface with no thickness, and interfacial force distributions acting on the bodies apart the interface. The proposed test cases which can serve as benchmarks for simulation codes, concern in a first step contact and perfectly plastic interface behavior (for illustrative purpose, on a 0D example). The last numerical test deals with contact, friction, fracture and adhesion for an extrinsic perfectly brittle interface behavior, to exemplify the feasibility on a full 3D finite element model.]]></description>
      <pubDate>Tue, 17 Sep 2024 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.11611</link>
      <guid>https://doi.org/10.46298/jtcam.11611</guid>
      <author>Dureisseix, David</author>
      <author>Larousse, Paul</author>
      <author>Gravouil, Anthony</author>
      <author>Di Stasio, Jean</author>
      <dc:creator>Dureisseix, David</dc:creator>
      <dc:creator>Larousse, Paul</dc:creator>
      <dc:creator>Gravouil, Anthony</dc:creator>
      <dc:creator>Di Stasio, Jean</dc:creator>
      <content:encoded><![CDATA[Dynamic systems, and in particular mechanical structures, may be subjected to non-smooth loadings such as impacts or shocks. Moreover, their behavior itself may exhibit more or less non-smooth evolutions, as when fracture occurs. Therefore, robust simulation models are of interest to capture such behaviors. A particular focus is made herein on time-stepping explicit dynamics schemes to allow efficient simulations, and non-smoothness is embedded within the discrete resolution model, so that robust simulations can be obtained, with a minimum number of numerical parameters. The original contributions of this article lie in the way the non-smooth behavior is formulated to be embedded in an explicit dynamics framework. This study focuses on the solver for dynamics with non-smooth interface behavior, rather than on the behavior models themselves. The applications concern non-smooth interface behaviors at macroscopic scale, between displacement jump on the 2D interface surface with no thickness, and interfacial force distributions acting on the bodies apart the interface. The proposed test cases which can serve as benchmarks for simulation codes, concern in a first step contact and perfectly plastic interface behavior (for illustrative purpose, on a 0D example). The last numerical test deals with contact, friction, fracture and adhesion for an extrinsic perfectly brittle interface behavior, to exemplify the feasibility on a full 3D finite element model.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Accounting for the mechanical response of the cell membrane during the uptake of random nanoparticles</title>
      <description><![CDATA[In order to improve the efficiency of the delivery of cancer treatments to cancer cells, the cellular uptake of nanoparticles (NPs), used as drug delivery systems, is numerically investigated through a mechanical approach. The objective is to optimize the NP's mechanical and geometrical properties to enhance their entry into cancer cells while avoiding benign ones. In previous studies, these properties are modeled as constant during the process of cellular uptake. However, recent observations of the displacement of the membrane's constituents towards the region in the cell membrane where the uptake of the NPs takes place show that the mechanical properties of the membrane vary during this process. Reason for writing The important contribution of adhesion to the wrapping process is already well documented in literature. It is therefore crucial to model this parameter properly as the conclusions made with a constant adhesion model may not be accurate compared to reality. Methodology Based on the existing knowledge on the reaction of membrane constituents to interaction with NPs, a 3-parameter sigmoidal function, accounting for the delay, amplitude, and speed of the reaction, has been used to model the evolution of adhesion. A variance-based sensitivity analysis has then been performed in order to quantify the influence of these parameters on the outputs of the model. Results It was found that the introduction of a variable adhesion tends to alter the predictions of endocytosis of NPs. The contribution of the amplitude and delay is respectively 0.32 and 0.43 times as important as that of the NP's aspect ratio, which is the prominent parameter. The influence of the slope of the transition is the least important parameter and does not appear to contribute to endocytosis. Implications Hence, models of the cellular uptake of NPs should use a variable, instead of constant, adhesion in order a representative as possible of the behavior of the cell membrane. The predictions are different from those obtained using a model with constant adhesion.]]></description>
      <pubDate>Sat, 14 Sep 2024 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.12489</link>
      <guid>https://doi.org/10.46298/jtcam.12489</guid>
      <author>Iaquinta, Sarah</author>
      <author>Khazaie, Shahram</author>
      <author>Jacquemin, Frédéric</author>
      <author>Fréour, Sylvain</author>
      <dc:creator>Iaquinta, Sarah</dc:creator>
      <dc:creator>Khazaie, Shahram</dc:creator>
      <dc:creator>Jacquemin, Frédéric</dc:creator>
      <dc:creator>Fréour, Sylvain</dc:creator>
      <content:encoded><![CDATA[In order to improve the efficiency of the delivery of cancer treatments to cancer cells, the cellular uptake of nanoparticles (NPs), used as drug delivery systems, is numerically investigated through a mechanical approach. The objective is to optimize the NP's mechanical and geometrical properties to enhance their entry into cancer cells while avoiding benign ones. In previous studies, these properties are modeled as constant during the process of cellular uptake. However, recent observations of the displacement of the membrane's constituents towards the region in the cell membrane where the uptake of the NPs takes place show that the mechanical properties of the membrane vary during this process. Reason for writing The important contribution of adhesion to the wrapping process is already well documented in literature. It is therefore crucial to model this parameter properly as the conclusions made with a constant adhesion model may not be accurate compared to reality. Methodology Based on the existing knowledge on the reaction of membrane constituents to interaction with NPs, a 3-parameter sigmoidal function, accounting for the delay, amplitude, and speed of the reaction, has been used to model the evolution of adhesion. A variance-based sensitivity analysis has then been performed in order to quantify the influence of these parameters on the outputs of the model. Results It was found that the introduction of a variable adhesion tends to alter the predictions of endocytosis of NPs. The contribution of the amplitude and delay is respectively 0.32 and 0.43 times as important as that of the NP's aspect ratio, which is the prominent parameter. The influence of the slope of the transition is the least important parameter and does not appear to contribute to endocytosis. Implications Hence, models of the cellular uptake of NPs should use a variable, instead of constant, adhesion in order a representative as possible of the behavior of the cell membrane. The predictions are different from those obtained using a model with constant adhesion.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Wedge indentation of elastoplastic solids — from single indentation to interaction between indenters</title>
      <description><![CDATA[Performance of metallic seals used between face-turned surfaces is related to their abilities to flow plastically in order to fill up cavities between wedge-shaped asperities. Double wedge indentation is therefore a simple way to investigate what happens at such a seal-flange interface. In this paper, finite element analyses of single and double wedge indentations are conducted. A particular attention is paid to the effects of hardening parameters on the resulting hardness. First, it is observed that single wedge indentation hardness can be well-approximated by the adaptation of analytic models initially developed for cone indentation problems. Second, it is shown that interaction between indentation-strain field during double wedge indentation starts once the bearing ratio is about 25%. It leads to a significant mean contact pressure increase, which is strongly dependent upon the strain hardening exponent. Eventually, for a bearing ratio higher than 75%, a plastic locking stage occurs, which leads to an exponential increase of the mean contact pressure. Practical applications of this work to indentation and sealing research fields are discussed.]]></description>
      <pubDate>Mon, 01 Apr 2024 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.8945</link>
      <guid>https://doi.org/10.46298/jtcam.8945</guid>
      <author>Marthouret, Yvan</author>
      <author>Zaouter, Tony</author>
      <author>Ledrappier, Florent</author>
      <author>Kermouche, Guillaume</author>
      <dc:creator>Marthouret, Yvan</dc:creator>
      <dc:creator>Zaouter, Tony</dc:creator>
      <dc:creator>Ledrappier, Florent</dc:creator>
      <dc:creator>Kermouche, Guillaume</dc:creator>
      <content:encoded><![CDATA[Performance of metallic seals used between face-turned surfaces is related to their abilities to flow plastically in order to fill up cavities between wedge-shaped asperities. Double wedge indentation is therefore a simple way to investigate what happens at such a seal-flange interface. In this paper, finite element analyses of single and double wedge indentations are conducted. A particular attention is paid to the effects of hardening parameters on the resulting hardness. First, it is observed that single wedge indentation hardness can be well-approximated by the adaptation of analytic models initially developed for cone indentation problems. Second, it is shown that interaction between indentation-strain field during double wedge indentation starts once the bearing ratio is about 25%. It leads to a significant mean contact pressure increase, which is strongly dependent upon the strain hardening exponent. Eventually, for a bearing ratio higher than 75%, a plastic locking stage occurs, which leads to an exponential increase of the mean contact pressure. Practical applications of this work to indentation and sealing research fields are discussed.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Robustness of the Data-Driven Identification algorithm with incomplete input data</title>
      <description><![CDATA[Identifying the mechanical response of a material without presupposing any constitutive equation is possible thanks to the Data-Driven Identification algorithm developed by the authors. It allows to measure stresses from displacement fields and forces applied to a given structure; the peculiarity of the technique is the absence of underlying constitutive equation. In the case of real experiments, the algorithm has been successfully applied on a perforated elastomer sheet deformed under large strain. Displacements are gathered with Digital Image Correlation and net forces with a load cell. However, those real data are incomplete for two reasons: some displacement values, close to the edges or in a noise-affected area, are missing and the force information is incomplete with respect to the original DDI algorithm requirements. The present study proves that with appropriate data handling, stress fields can be identified in a robust manner. The solution relies on recovering those missing data in a way that no assumption, except the balance of linear momentum, has to be made. The influence of input parameters of the method is also discussed. The overall study is conducted on synthetic data: perfect and incomplete data are used to prove robustness of the proposed solutions. Therefore, the paper can be considered as a practical guide for implementing the DDI method.]]></description>
      <pubDate>Wed, 21 Feb 2024 21:44:21 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.12590</link>
      <guid>https://doi.org/10.46298/jtcam.12590</guid>
      <author>Dalémat, Marie</author>
      <author>Coret, Michel</author>
      <author>Leygue, Adrien</author>
      <author>Verron, Erwan</author>
      <dc:creator>Dalémat, Marie</dc:creator>
      <dc:creator>Coret, Michel</dc:creator>
      <dc:creator>Leygue, Adrien</dc:creator>
      <dc:creator>Verron, Erwan</dc:creator>
      <content:encoded><![CDATA[Identifying the mechanical response of a material without presupposing any constitutive equation is possible thanks to the Data-Driven Identification algorithm developed by the authors. It allows to measure stresses from displacement fields and forces applied to a given structure; the peculiarity of the technique is the absence of underlying constitutive equation. In the case of real experiments, the algorithm has been successfully applied on a perforated elastomer sheet deformed under large strain. Displacements are gathered with Digital Image Correlation and net forces with a load cell. However, those real data are incomplete for two reasons: some displacement values, close to the edges or in a noise-affected area, are missing and the force information is incomplete with respect to the original DDI algorithm requirements. The present study proves that with appropriate data handling, stress fields can be identified in a robust manner. The solution relies on recovering those missing data in a way that no assumption, except the balance of linear momentum, has to be made. The influence of input parameters of the method is also discussed. The overall study is conducted on synthetic data: perfect and incomplete data are used to prove robustness of the proposed solutions. Therefore, the paper can be considered as a practical guide for implementing the DDI method.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>An energy approach to asymptotic, higher-order, linear homogenization</title>
      <description><![CDATA[A higher-order homogenization method for linear elastic structures is proposed. While most existing approaches to homogenization start from the equations of equilibrium, the proposed one works at the energy level. We start from an energy functional depending on microscopic degrees of freedom on the one hand and on macroscopic variables on the other hand; the homogenized energy functional is derived by relaxing the microscopic degrees of freedom and applying a formal two-scale expansion. This method delivers the energy functional of the homogenized model directly, including boundary terms that have not been discussed in previous work. Our method is formulated in a generic setting which makes it applicable to a variety of geometries in dimension 1, 2 or 3, and without any particular assumption on material symmetry. An implementation using a symbolic calculation language is proposed and it is distributed as an open-source library. Simple illustrations to elastic trusses having pre-stress or graded elastic properties are presented. The approach is presented in the context of discrete elastic structures and the connection with previous work on the higher-order homogenization of period continua is discussed.]]></description>
      <pubDate>Tue, 19 Dec 2023 11:03:49 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.11414</link>
      <guid>https://doi.org/10.46298/jtcam.11414</guid>
      <author>Audoly, Basile</author>
      <author>Lestringant, Claire</author>
      <dc:creator>Audoly, Basile</dc:creator>
      <dc:creator>Lestringant, Claire</dc:creator>
      <content:encoded><![CDATA[A higher-order homogenization method for linear elastic structures is proposed. While most existing approaches to homogenization start from the equations of equilibrium, the proposed one works at the energy level. We start from an energy functional depending on microscopic degrees of freedom on the one hand and on macroscopic variables on the other hand; the homogenized energy functional is derived by relaxing the microscopic degrees of freedom and applying a formal two-scale expansion. This method delivers the energy functional of the homogenized model directly, including boundary terms that have not been discussed in previous work. Our method is formulated in a generic setting which makes it applicable to a variety of geometries in dimension 1, 2 or 3, and without any particular assumption on material symmetry. An implementation using a symbolic calculation language is proposed and it is distributed as an open-source library. Simple illustrations to elastic trusses having pre-stress or graded elastic properties are presented. The approach is presented in the context of discrete elastic structures and the connection with previous work on the higher-order homogenization of period continua is discussed.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Solving viscoelastic problems with a Laplace transform approach supplanted by ARX models, suggesting a way to upgrade Finite Element or spectral codes</title>
      <description><![CDATA[Finite Element codes used for solving the mechanical equilibrium equations in transient problems associated to (time-dependent) viscoelastic media generally relies on time-discretized versions of the selected constitutive law. Recent concerns about the use of non-integer differential equations to describe viscoelasticity or well-founded ideas based upon the use of a behavior's law directly derived from Dynamic Mechanical Analysis (DMA) experiments in frequency domain, could make the Laplace domain approach particularly attractive if embedded in a time discretized scheme. Based upon the inversion of Laplace transforms, this paper shows that this aim is not only possible but also gives rise to a simple algorithm having good performances in terms of computation times and precision. Such an approach, which fully relies on the Laplace-defined Behavioral Transfer Function (LTBF) can be promoted if it uses AutoRegressive with eXogeneous input parametric models perfectly substitutable to the real LTBF. They avoid the hitherto prohibitive pitfall of having to store all past data in the computer's memory while maintaining an equal computation precision.]]></description>
      <pubDate>Tue, 10 Oct 2023 16:03:55 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.10304</link>
      <guid>https://doi.org/10.46298/jtcam.10304</guid>
      <author>André, Stéphane</author>
      <author>Noûs, Camille</author>
      <dc:creator>André, Stéphane</dc:creator>
      <dc:creator>Noûs, Camille</dc:creator>
      <content:encoded><![CDATA[Finite Element codes used for solving the mechanical equilibrium equations in transient problems associated to (time-dependent) viscoelastic media generally relies on time-discretized versions of the selected constitutive law. Recent concerns about the use of non-integer differential equations to describe viscoelasticity or well-founded ideas based upon the use of a behavior's law directly derived from Dynamic Mechanical Analysis (DMA) experiments in frequency domain, could make the Laplace domain approach particularly attractive if embedded in a time discretized scheme. Based upon the inversion of Laplace transforms, this paper shows that this aim is not only possible but also gives rise to a simple algorithm having good performances in terms of computation times and precision. Such an approach, which fully relies on the Laplace-defined Behavioral Transfer Function (LTBF) can be promoted if it uses AutoRegressive with eXogeneous input parametric models perfectly substitutable to the real LTBF. They avoid the hitherto prohibitive pitfall of having to store all past data in the computer's memory while maintaining an equal computation precision.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Efficient Computation of Redundancy Matrices for Moderately Redundant Truss and Frame Structures</title>
      <description><![CDATA[Large statically indeterminate truss and frame structures exhibit complex load-bearing behavior, and redundancy matrices are helpful for their analysis and design. Depending on the task, the full redundancy matrix or only its diagonal entries are required. The standard computation procedure has a high computational effort. Many structures fall in the category of moderately redundant, i.e., the ratio of the statical indeterminacy to the number of all load-carrying modes of all elements is less one half. This paper proposes a closed-form expression for redundancy contributions that is computationally efficient for moderately redundant systems. The expression is derived via a factorization of the redundancy matrix that is based on singular value decomposition. Several examples illustrate the behavior of the method for increasing size of systems and, where applicable, for increasing degree of statical indeterminacy.]]></description>
      <pubDate>Wed, 27 Sep 2023 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.11056</link>
      <guid>https://doi.org/10.46298/jtcam.11056</guid>
      <author>Tkachuk, Anton</author>
      <author>Krake, Tim</author>
      <author>Gade, Jan</author>
      <author>von Scheven, Malte</author>
      <dc:creator>Tkachuk, Anton</dc:creator>
      <dc:creator>Krake, Tim</dc:creator>
      <dc:creator>Gade, Jan</dc:creator>
      <dc:creator>von Scheven, Malte</dc:creator>
      <content:encoded><![CDATA[Large statically indeterminate truss and frame structures exhibit complex load-bearing behavior, and redundancy matrices are helpful for their analysis and design. Depending on the task, the full redundancy matrix or only its diagonal entries are required. The standard computation procedure has a high computational effort. Many structures fall in the category of moderately redundant, i.e., the ratio of the statical indeterminacy to the number of all load-carrying modes of all elements is less one half. This paper proposes a closed-form expression for redundancy contributions that is computationally efficient for moderately redundant systems. The expression is derived via a factorization of the redundancy matrix that is based on singular value decomposition. Several examples illustrate the behavior of the method for increasing size of systems and, where applicable, for increasing degree of statical indeterminacy.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Crack branching at low tip speeds: spilling the T</title>
      <description><![CDATA[Using the criterion that a crack will extend along the direction of maximum circumferential stress, this paper demonstrates the influence of the coupling between the crack-parallel T-stress and the tip speed on the directional (in)stability of dynamics cracks in brittle materials, i.e., branching, turning, and limiting velocities. The proposed (in)stability criterion evolves within the theory of dynamic fracture: we build on the work of Ramulu and Kobayashi (1983) by introducing a reference distance ahead of the crack-tip to incorporate the contribution of the higher-order terms in the asymptotic solution of the elastic crack-tip fields. The theoretical aspect is first explored, a methodology to numerically (and experimentally) advocate the instability—as a co-action of T-stress and a fast-running crack—is then proposed and validated on Borden et al. (2012)’s branching benchmark. An experimental setup combining Ultra-High-Speed High-Resolution imaging with advanced Digital Image Correlation algorithms and a novel crack-branching inertial impact test enables for never-seen-before quantification of the rich dynamical behaviour of the fracture. This permits the experimental validation of the developed crack (in)stability criterion.]]></description>
      <pubDate>Thu, 17 Aug 2023 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.10172</link>
      <guid>https://doi.org/10.46298/jtcam.10172</guid>
      <author>Eid, Elie</author>
      <author>Seghir, Rian</author>
      <author>Réthoré, Julien</author>
      <dc:creator>Eid, Elie</dc:creator>
      <dc:creator>Seghir, Rian</dc:creator>
      <dc:creator>Réthoré, Julien</dc:creator>
      <content:encoded><![CDATA[Using the criterion that a crack will extend along the direction of maximum circumferential stress, this paper demonstrates the influence of the coupling between the crack-parallel T-stress and the tip speed on the directional (in)stability of dynamics cracks in brittle materials, i.e., branching, turning, and limiting velocities. The proposed (in)stability criterion evolves within the theory of dynamic fracture: we build on the work of Ramulu and Kobayashi (1983) by introducing a reference distance ahead of the crack-tip to incorporate the contribution of the higher-order terms in the asymptotic solution of the elastic crack-tip fields. The theoretical aspect is first explored, a methodology to numerically (and experimentally) advocate the instability—as a co-action of T-stress and a fast-running crack—is then proposed and validated on Borden et al. (2012)’s branching benchmark. An experimental setup combining Ultra-High-Speed High-Resolution imaging with advanced Digital Image Correlation algorithms and a novel crack-branching inertial impact test enables for never-seen-before quantification of the rich dynamical behaviour of the fracture. This permits the experimental validation of the developed crack (in)stability criterion.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>The average conformation tensor of inter-atomic bonds as an alternative state variable to the strain tensor: definition and first application — the case of nanoelasticity</title>
      <description><![CDATA[Most of the mechanical models for solid state materials are in a methodological framework where a strain tensor, whatever it is, is considered as a thermodynamic state variable. As a consequence, the Cauchy stress tensor is expressed as a function of a strain tensor—and, in many cases, of one or more other state variables, such as the temperature. Such a choice for the kinematic state variable is clearly relevant in the case of infinitesimal or finite elasticity. However, one can ask whether an alternative state variable could not be considered. In the case of finite elastoplasticity, the choice of a strain tensor as the basic, kinematic state variable is not totally without issue, in particular in relation to the physical meaning of the internal state variable describing the permanent strains. In any case, this paper proposes an alternative to the strain tensor as a state variable, which is not based on the deformation (Lagrangian) gradient: the average conformation tensor of inter-atomic bonds. The purpose, however, is restricted to (1) a particular type of materials, namely the pure substances (copper or aluminum, for instance), (2) the nanoscale, and (3) the case of elasticity. The very simple case of two atoms of a pure substance in the solid state is first considered. It is shown that the kinematics of the inter-atomic bond can be characterized by a so called ``conformation'' tensor, and that the tensorial internal force acting on it can be immediately deduced from a single scalar function, depending only on the conformation tensor: the state potential of free energy (or interaction potential). Using an averaging procedure, these notions are then extended to a finite set of atoms, namely an atom and its first neighbours, which can be seen as the ``unit cell'' of a pure substance in the solid state considered as a discrete medium. They are also transposed to the Continuum case, where an expression of the Cauchy stress tensor is proposed as the first derivative of a state potential of density (per unit mass) of average free energy of inter-atomic bonds, which is an explicit function of the average conformation tensor of inter-atomic bonds. By applying a standard procedure in Continuum Thermodynamics, it is then shown that the objective part of the material derivative of this new state variable, at least in the case when the pure substance can be considered as an elastic medium, is equal to the symmetric part of the Eulerian velocity gradient, that is the rate of deformation tensor. In the case of uniaxial tension, a simple relationship is eventually set out between the average conformation tensor and a strain tensor, which is correctly approximated by the usual infinitesimal strain tensor as long as the conformation variations (from an initial state of conformation) are ``small''. From this latter result, and assuming an elastic behavior, a simple expression for the state potential of density of average free energy is inferred, showing great similarities with—but not equivalent to—the classical model of isotropic, linear elasticity (Hooke's law).]]></description>
      <pubDate>Mon, 05 Jun 2023 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7366</link>
      <guid>https://doi.org/10.46298/jtcam.7366</guid>
      <author>Désoyer, Thierry</author>
      <dc:creator>Désoyer, Thierry</dc:creator>
      <content:encoded><![CDATA[Most of the mechanical models for solid state materials are in a methodological framework where a strain tensor, whatever it is, is considered as a thermodynamic state variable. As a consequence, the Cauchy stress tensor is expressed as a function of a strain tensor—and, in many cases, of one or more other state variables, such as the temperature. Such a choice for the kinematic state variable is clearly relevant in the case of infinitesimal or finite elasticity. However, one can ask whether an alternative state variable could not be considered. In the case of finite elastoplasticity, the choice of a strain tensor as the basic, kinematic state variable is not totally without issue, in particular in relation to the physical meaning of the internal state variable describing the permanent strains. In any case, this paper proposes an alternative to the strain tensor as a state variable, which is not based on the deformation (Lagrangian) gradient: the average conformation tensor of inter-atomic bonds. The purpose, however, is restricted to (1) a particular type of materials, namely the pure substances (copper or aluminum, for instance), (2) the nanoscale, and (3) the case of elasticity. The very simple case of two atoms of a pure substance in the solid state is first considered. It is shown that the kinematics of the inter-atomic bond can be characterized by a so called ``conformation'' tensor, and that the tensorial internal force acting on it can be immediately deduced from a single scalar function, depending only on the conformation tensor: the state potential of free energy (or interaction potential). Using an averaging procedure, these notions are then extended to a finite set of atoms, namely an atom and its first neighbours, which can be seen as the ``unit cell'' of a pure substance in the solid state considered as a discrete medium. They are also transposed to the Continuum case, where an expression of the Cauchy stress tensor is proposed as the first derivative of a state potential of density (per unit mass) of average free energy of inter-atomic bonds, which is an explicit function of the average conformation tensor of inter-atomic bonds. By applying a standard procedure in Continuum Thermodynamics, it is then shown that the objective part of the material derivative of this new state variable, at least in the case when the pure substance can be considered as an elastic medium, is equal to the symmetric part of the Eulerian velocity gradient, that is the rate of deformation tensor. In the case of uniaxial tension, a simple relationship is eventually set out between the average conformation tensor and a strain tensor, which is correctly approximated by the usual infinitesimal strain tensor as long as the conformation variations (from an initial state of conformation) are ``small''. From this latter result, and assuming an elastic behavior, a simple expression for the state potential of density of average free energy is inferred, showing great similarities with—but not equivalent to—the classical model of isotropic, linear elasticity (Hooke's law).]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Revealing systematic errors in hole drilling measurements through a calibration bench: the case of zero-depth data</title>
      <description><![CDATA[An accurate estimation of the measurement error in the hole drilling method is needed to choose an appropriate level of regularization and to perform a sensitivity analysis on the stress results. The latest release of ASTM E837 standard for the hole drilling method includes a procedure aimed at estimatingthe standard deviation of the random error component on strain measurements, proposed by Schajer. Nevertheless, strain measurements are also affected to some extent by systematic errors which are not included in the estimation and need to be compensated. For example, an error in the rosette gage factor orin the identification of the zero-depth datum systematically affects all strain measurements in a strongly correlated fashion. This paper describes a calibration bench, designed to superimpose a reference bending stress distribution on a given specimen while simultaneously performing a hole drilling measurement.Since the reference solution is known a priori and shares the measurement instrumentation, the hole geometry and the stepping process with the actual residual stress distribution, the bench provides the user with a direct validation of the obtained accuracy. In addition, strategies aimed at compensating systematicerrors can be tested on the reference solution and then applied on the residual stress evaluation. The imperfect hole geometry and drilling alignment are proven to cause a significant underestimation of stresses near the surface, as they lead to an incorrect identification of the zero-depth datum. It is shown that this effect can be corrected through the proposed calibration bench.]]></description>
      <pubDate>Mon, 05 Jun 2023 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.10080</link>
      <guid>https://doi.org/10.46298/jtcam.10080</guid>
      <author>Beghini, Marco</author>
      <author>Grossi, Tommaso</author>
      <author>Santus, Ciro</author>
      <author>Valentini, Emilio</author>
      <dc:creator>Beghini, Marco</dc:creator>
      <dc:creator>Grossi, Tommaso</dc:creator>
      <dc:creator>Santus, Ciro</dc:creator>
      <dc:creator>Valentini, Emilio</dc:creator>
      <content:encoded><![CDATA[An accurate estimation of the measurement error in the hole drilling method is needed to choose an appropriate level of regularization and to perform a sensitivity analysis on the stress results. The latest release of ASTM E837 standard for the hole drilling method includes a procedure aimed at estimatingthe standard deviation of the random error component on strain measurements, proposed by Schajer. Nevertheless, strain measurements are also affected to some extent by systematic errors which are not included in the estimation and need to be compensated. For example, an error in the rosette gage factor orin the identification of the zero-depth datum systematically affects all strain measurements in a strongly correlated fashion. This paper describes a calibration bench, designed to superimpose a reference bending stress distribution on a given specimen while simultaneously performing a hole drilling measurement.Since the reference solution is known a priori and shares the measurement instrumentation, the hole geometry and the stepping process with the actual residual stress distribution, the bench provides the user with a direct validation of the obtained accuracy. In addition, strategies aimed at compensating systematicerrors can be tested on the reference solution and then applied on the residual stress evaluation. The imperfect hole geometry and drilling alignment are proven to cause a significant underestimation of stresses near the surface, as they lead to an incorrect identification of the zero-depth datum. It is shown that this effect can be corrected through the proposed calibration bench.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Reduced-order modeling of geometrically nonlinear rotating structures using the direct parametrisation of invariant manifolds</title>
      <description><![CDATA[The direct parametrisation method for invariant manifolds is a nonlinear reduction technique which derives nonlinear mappings and reduced-order dynamics that describe the evolution of dynamical systems along a low-dimensional invariant-based span of the phase space. It can be directly applied to finite element problems. When the development is performed using an arbitrary order asymptotic expansion, it provides an efficient reduced-order modeling strategy for geometrically nonlinear structures. It is here applied to the case of rotating structures featuring centrifugal effect. A rotating cantilever beam with large amplitude vibrations is first selected in order to highlight the main features of the method. Numerical results show that the method provides accurate reduced-order models (ROMs) for any rotation speed and vibration amplitude of interest with a single master mode, thus offering remarkable reduction in the computational burden. The hardening/softening transition of the fundamental flexural mode with increasing rotation speed is then investigated in detail and a ROM parametrised with respect to rotation speed and forcing frequencies is detailed. The method is then applied to a twisted plate model representative of a fan blade, showing how the technique can handle more complex structures. Hardening/softening transition is also investigated as well as interpolation of ROMs, highlighting the efficacy of the method.]]></description>
      <pubDate>Thu, 01 Jun 2023 15:46:07 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.10430</link>
      <guid>https://doi.org/10.46298/jtcam.10430</guid>
      <author>Martin, Adrien</author>
      <author>Opreni, Andrea</author>
      <author>Vizzaccaro, Alessandra</author>
      <author>Debeurre, Marielle</author>
      <author>Salles, Loic</author>
      <author>Frangi, Attilio</author>
      <author>Thomas, Olivier</author>
      <author>Touzé, Cyril</author>
      <dc:creator>Martin, Adrien</dc:creator>
      <dc:creator>Opreni, Andrea</dc:creator>
      <dc:creator>Vizzaccaro, Alessandra</dc:creator>
      <dc:creator>Debeurre, Marielle</dc:creator>
      <dc:creator>Salles, Loic</dc:creator>
      <dc:creator>Frangi, Attilio</dc:creator>
      <dc:creator>Thomas, Olivier</dc:creator>
      <dc:creator>Touzé, Cyril</dc:creator>
      <content:encoded><![CDATA[The direct parametrisation method for invariant manifolds is a nonlinear reduction technique which derives nonlinear mappings and reduced-order dynamics that describe the evolution of dynamical systems along a low-dimensional invariant-based span of the phase space. It can be directly applied to finite element problems. When the development is performed using an arbitrary order asymptotic expansion, it provides an efficient reduced-order modeling strategy for geometrically nonlinear structures. It is here applied to the case of rotating structures featuring centrifugal effect. A rotating cantilever beam with large amplitude vibrations is first selected in order to highlight the main features of the method. Numerical results show that the method provides accurate reduced-order models (ROMs) for any rotation speed and vibration amplitude of interest with a single master mode, thus offering remarkable reduction in the computational burden. The hardening/softening transition of the fundamental flexural mode with increasing rotation speed is then investigated in detail and a ROM parametrised with respect to rotation speed and forcing frequencies is detailed. The method is then applied to a twisted plate model representative of a fan blade, showing how the technique can handle more complex structures. Hardening/softening transition is also investigated as well as interpolation of ROMs, highlighting the efficacy of the method.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Optimization of a dynamic absorber with nonlinear stiffness and damping for the vibration control of a floating offshore wind turbine toy model</title>
      <description><![CDATA[Passive vibration mitigation of offshore wind turbines using nonlinear absorbers or nonlinear energy sinks has started to receive attention in the literature. In most cases, little attention has been paid to the possibility of detached resonances that occur when the nonlinear energy sink is attached to the linear system describing the wind turbine. Sea motions that alter the initial conditions of the floating offshore wind turbine may cause the nonlinear energy sink to operate at one or more detached resonances, completely negating its ability to control turbine vibration. In this paper, we are interested in optimizing the parameters of a nonlinear energy sink with nonlinear stiffness and nonlinear viscous damping for vibration control of a toy model (e.g., a linear mass-spring-damper system) of a floating offshore wind turbine over its entire operating range. The mechanism of cancellation of the detached resonance is studied analytically under 1:1 resonance. It is shown that the nonlinear energy sink with properly tuned nonlinear viscous damping allows the complete elimination of undesired regimes and completely restores the absorber's ability to strongly limit the vibration of a floating offshore wind turbine over its entire forcing range. The results obtained over a wide range of parameters suggest that both the optimal nonlinear energy sink parameters (linear and nonlinear stiffness and nonlinear damping) and the damping of floating offshore wind turbine vibration depend on simple power laws of nonlinear energy sink mass and linear damping.]]></description>
      <pubDate>Thu, 11 May 2023 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.10123</link>
      <guid>https://doi.org/10.46298/jtcam.10123</guid>
      <author>Mattei, Pierre-Olivier</author>
      <author>Côte, Renaud</author>
      <dc:creator>Mattei, Pierre-Olivier</dc:creator>
      <dc:creator>Côte, Renaud</dc:creator>
      <content:encoded><![CDATA[Passive vibration mitigation of offshore wind turbines using nonlinear absorbers or nonlinear energy sinks has started to receive attention in the literature. In most cases, little attention has been paid to the possibility of detached resonances that occur when the nonlinear energy sink is attached to the linear system describing the wind turbine. Sea motions that alter the initial conditions of the floating offshore wind turbine may cause the nonlinear energy sink to operate at one or more detached resonances, completely negating its ability to control turbine vibration. In this paper, we are interested in optimizing the parameters of a nonlinear energy sink with nonlinear stiffness and nonlinear viscous damping for vibration control of a toy model (e.g., a linear mass-spring-damper system) of a floating offshore wind turbine over its entire operating range. The mechanism of cancellation of the detached resonance is studied analytically under 1:1 resonance. It is shown that the nonlinear energy sink with properly tuned nonlinear viscous damping allows the complete elimination of undesired regimes and completely restores the absorber's ability to strongly limit the vibration of a floating offshore wind turbine over its entire forcing range. The results obtained over a wide range of parameters suggest that both the optimal nonlinear energy sink parameters (linear and nonlinear stiffness and nonlinear damping) and the damping of floating offshore wind turbine vibration depend on simple power laws of nonlinear energy sink mass and linear damping.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Mathematics of stable tensegrity structures</title>
      <description><![CDATA[Tensegrity structures have been extensively studied over the last years due to their potential applications in modern engineering like metamaterials, deployable structures, planetary lander modules, etc. Many of the form-finding methods proposed continue to produce structures with one or more soft/swinging modes. These modes have been vividly highlighted and outlined as the grounds for these structures to be unsuitable as engineering structures. This work proposes a relationship between the number of rods and strings to satisfy the full-rank convexity criterion as a part of the form-finding process. Using the proposed form-finding process for the famous three-rod tensegrity, the work proposes an alternative three-rod ten-string that is stable. The work demonstrates that the stable tensegrities suitable for engineering are feasible and can be designed.]]></description>
      <pubDate>Fri, 05 May 2023 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7337</link>
      <guid>https://doi.org/10.46298/jtcam.7337</guid>
      <author>Harish, Ajay B.</author>
      <author>Nandurdikar, Vijay</author>
      <author>Deshpande, Shubham</author>
      <author>Andress, Stephanie</author>
      <dc:creator>Harish, Ajay B.</dc:creator>
      <dc:creator>Nandurdikar, Vijay</dc:creator>
      <dc:creator>Deshpande, Shubham</dc:creator>
      <dc:creator>Andress, Stephanie</dc:creator>
      <content:encoded><![CDATA[Tensegrity structures have been extensively studied over the last years due to their potential applications in modern engineering like metamaterials, deployable structures, planetary lander modules, etc. Many of the form-finding methods proposed continue to produce structures with one or more soft/swinging modes. These modes have been vividly highlighted and outlined as the grounds for these structures to be unsuitable as engineering structures. This work proposes a relationship between the number of rods and strings to satisfy the full-rank convexity criterion as a part of the form-finding process. Using the proposed form-finding process for the famous three-rod tensegrity, the work proposes an alternative three-rod ten-string that is stable. The work demonstrates that the stable tensegrities suitable for engineering are feasible and can be designed.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Plasticity and ductility of an anisotropic recrystallized AA2198 Al-Cu-Li alloy in T3 and T8 conditions during proportional and non-proportional loading paths: simulations and experiments</title>
      <description><![CDATA[The anisotropic material behaviour of a recrystallized AA2198 Al-Cu-Li alloy in T3 and T8 conditions was assessed by proportional loading of uniaxial-tension specimens in rolling (L), transverse (T) and diagonal (D) orientations. The width and longitudinal strains were measured to quantify plastic anisotropy. Notched-tension samples were tested in L and T directions. The material showed weak anisotropy in terms of stress strain curves and a moderate plastic anisotropy, consistent with its texture obtained by EBSD. An anisotropic Bron-Besson type material model was identified using this data base and a micro shear-only (SO) test. The model succeeded in predicting the behaviour of micro specimens for proportional tension-only (TO) loading and non-proportional load path changes including 'shear to tension' (ST) as well as 'tension to shear' (TS) tests. The non-proportional loading was achieved using a newly designed cross shaped sample. It was loaded in one direction, unloaded and subsequently loaded in the orthogonal direction till fracture. The average stretch to fracture of both alloys measured by a four point frame optical extensometer decreased by 29 % and 16 % for T3 and T8 respectively for the 'shear to tension' experiment compared to the proportional TO experiment. The average stretch to fracture of 'tension to shear' tests was reduced by 10 % for 2198T3 and hardly reduced for 2198T8 compared to the stretch to fracture of the SO tests, but subject to strong scatter. FE simulations showed local accumulated strain to fracture values that were similar for all loading histories for the T8 condition (0.73 − 0.84). Lower strain to fracture values were found in T3 condition (0.45 − 0.73), despite the enhanced macroscopic ductility in tension. This was attributed to larger less localized plastic zones, especially for the ST test. The ductility scatter was attributed to necking and damage development in tension that can affect strain localization, associated fracture path and ductility, as observed by DIC and fractography.]]></description>
      <pubDate>Sun, 12 Mar 2023 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.8913</link>
      <guid>https://doi.org/10.46298/jtcam.8913</guid>
      <author>Kong, Xiang</author>
      <author>Chen, Jianqiang</author>
      <author>Madi, Yazid</author>
      <author>Missoum-Benziane, Djamel</author>
      <author>Besson, Jacques</author>
      <author>Morgeneyer, Thilo, F.</author>
      <dc:creator>Kong, Xiang</dc:creator>
      <dc:creator>Chen, Jianqiang</dc:creator>
      <dc:creator>Madi, Yazid</dc:creator>
      <dc:creator>Missoum-Benziane, Djamel</dc:creator>
      <dc:creator>Besson, Jacques</dc:creator>
      <dc:creator>Morgeneyer, Thilo, F.</dc:creator>
      <content:encoded><![CDATA[The anisotropic material behaviour of a recrystallized AA2198 Al-Cu-Li alloy in T3 and T8 conditions was assessed by proportional loading of uniaxial-tension specimens in rolling (L), transverse (T) and diagonal (D) orientations. The width and longitudinal strains were measured to quantify plastic anisotropy. Notched-tension samples were tested in L and T directions. The material showed weak anisotropy in terms of stress strain curves and a moderate plastic anisotropy, consistent with its texture obtained by EBSD. An anisotropic Bron-Besson type material model was identified using this data base and a micro shear-only (SO) test. The model succeeded in predicting the behaviour of micro specimens for proportional tension-only (TO) loading and non-proportional load path changes including 'shear to tension' (ST) as well as 'tension to shear' (TS) tests. The non-proportional loading was achieved using a newly designed cross shaped sample. It was loaded in one direction, unloaded and subsequently loaded in the orthogonal direction till fracture. The average stretch to fracture of both alloys measured by a four point frame optical extensometer decreased by 29 % and 16 % for T3 and T8 respectively for the 'shear to tension' experiment compared to the proportional TO experiment. The average stretch to fracture of 'tension to shear' tests was reduced by 10 % for 2198T3 and hardly reduced for 2198T8 compared to the stretch to fracture of the SO tests, but subject to strong scatter. FE simulations showed local accumulated strain to fracture values that were similar for all loading histories for the T8 condition (0.73 − 0.84). Lower strain to fracture values were found in T3 condition (0.45 − 0.73), despite the enhanced macroscopic ductility in tension. This was attributed to larger less localized plastic zones, especially for the ST test. The ductility scatter was attributed to necking and damage development in tension that can affect strain localization, associated fracture path and ductility, as observed by DIC and fractography.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Thermal and energy analysis of DMTA tests</title>
      <description><![CDATA[This paper investigates the suitability of the isothermal linear viscoelastic framework to describe the behavior of polymers observed during DMTA tests. A good interpretation of these tests is important because, in practice, they are used to construct master curves using the time-temperature superposition principle at small strain. These curves are then considered to predict the material behavior under experimentally unreachable thermal and/or loading frequency conditions. Currently, the DMTA protocol neglects the temperature variations induced by the deformation of polymers. We wonder if these temperature variations can have an influence on the measurement of dynamic moduli. To answer this question, quantitative infrared techniques were developed and used to assess small temperature variations of samples undergoing cyclic loadings during mechanical spectrometry tests. Thermal and mechanical data were used to quantify the viscous dissipated and the thermoelastic coupling energies that can be both associated with the hysteretic stress-strain response of polymers. Energy balances were then performed to quantify the relative importance of dissipative and thermoelastic coupling heat sources. From the energy standpoint, it is found that the thermoelastic energy rate was dozens of times higher than the dissipation. Especially at low frequencies, thermoelastic effects can have a greater influence on the loss modulus value than viscosity.]]></description>
      <pubDate>Wed, 08 Mar 2023 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.9726</link>
      <guid>https://doi.org/10.46298/jtcam.9726</guid>
      <author>Chrysochoos, André</author>
      <author>Arnould, Olivier</author>
      <dc:creator>Chrysochoos, André</dc:creator>
      <dc:creator>Arnould, Olivier</dc:creator>
      <content:encoded><![CDATA[This paper investigates the suitability of the isothermal linear viscoelastic framework to describe the behavior of polymers observed during DMTA tests. A good interpretation of these tests is important because, in practice, they are used to construct master curves using the time-temperature superposition principle at small strain. These curves are then considered to predict the material behavior under experimentally unreachable thermal and/or loading frequency conditions. Currently, the DMTA protocol neglects the temperature variations induced by the deformation of polymers. We wonder if these temperature variations can have an influence on the measurement of dynamic moduli. To answer this question, quantitative infrared techniques were developed and used to assess small temperature variations of samples undergoing cyclic loadings during mechanical spectrometry tests. Thermal and mechanical data were used to quantify the viscous dissipated and the thermoelastic coupling energies that can be both associated with the hysteretic stress-strain response of polymers. Energy balances were then performed to quantify the relative importance of dissipative and thermoelastic coupling heat sources. From the energy standpoint, it is found that the thermoelastic energy rate was dozens of times higher than the dissipation. Especially at low frequencies, thermoelastic effects can have a greater influence on the loss modulus value than viscosity.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Fatigue crack growth under large scale yielding condition: a tool based on explicit crack growth</title>
      <description><![CDATA[Fatigue crack growth under large-scale yielding condition is studied for high-temperature loading. The applied strains are so important that diffuse damage phenomena are visible as a network of micro-cracks in front of the major crack. The survey of a macroscopic cracked surface is nevertheless possible, and numerical simulations with explicit representation of this crack are carried out to evaluate crack driving forces. The proposed numerical scheme takes into account plastic wake in the course of crack growth in a 3D model. A non-local model of fatigue crack growth rate, based on partition of strain energy density into elastic and plastic terms, yields improved results as compared to classical assessment of ∆J by numerical methods.]]></description>
      <pubDate>Thu, 02 Feb 2023 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.9296</link>
      <guid>https://doi.org/10.46298/jtcam.9296</guid>
      <author>Maurel, Vincent</author>
      <author>Chiaruttini, Vincent</author>
      <author>Köster, Alain</author>
      <author>Missoum-Benziane, Djamel</author>
      <dc:creator>Maurel, Vincent</dc:creator>
      <dc:creator>Chiaruttini, Vincent</dc:creator>
      <dc:creator>Köster, Alain</dc:creator>
      <dc:creator>Missoum-Benziane, Djamel</dc:creator>
      <content:encoded><![CDATA[Fatigue crack growth under large-scale yielding condition is studied for high-temperature loading. The applied strains are so important that diffuse damage phenomena are visible as a network of micro-cracks in front of the major crack. The survey of a macroscopic cracked surface is nevertheless possible, and numerical simulations with explicit representation of this crack are carried out to evaluate crack driving forces. The proposed numerical scheme takes into account plastic wake in the course of crack growth in a 3D model. A non-local model of fatigue crack growth rate, based on partition of strain energy density into elastic and plastic terms, yields improved results as compared to classical assessment of ∆J by numerical methods.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Machine learning and micromechanics as allies to establish composition-property correlations in cement pastes</title>
      <description><![CDATA[Composition-property correlations are fundamental to understand cement-based materials behavior and optimize their formulation. Modelling based on fundamental material component constitutes a reliable tool to establish these correlations with the advantage of better exploring formulation space when compared with the often adopted experimental trial-and-error approaches. In this context, Machine Learning (ML) and Micromechanics-Based (MB) methods have been concurrently used for property prediction from material composition. Here, we show that these techniques can be allies for establishing composition-property correlations. We focus on predictions of Ordinary Portland Cement pastes elastic properties, but the outlined strategy can be extended to other cement systems. Various microstructures representations are considered in MB estimates, including multiscale representations and representations with ellipsoidal inclusions. In contrast, ML predictions do not need any a priori assumption on material microstructure. Predictions using ML and MB yield similar accuracy when compared against test datasets (but ML performed much better regarding the error estimated in training datasets). Working as allies, ML can be deployed to evaluate the (lack of) knowledge over the multi-dimensional parametric domains, and micromechanics provides a theoretical background for property data curation and is a tool to make up for missing data in databases.]]></description>
      <pubDate>Wed, 25 Jan 2023 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.9830</link>
      <guid>https://doi.org/10.46298/jtcam.9830</guid>
      <author>Honorio, Tulio</author>
      <author>Hamadouche, Sofiane, Ait</author>
      <author>Fau, Amélie</author>
      <dc:creator>Honorio, Tulio</dc:creator>
      <dc:creator>Hamadouche, Sofiane, Ait</dc:creator>
      <dc:creator>Fau, Amélie</dc:creator>
      <content:encoded><![CDATA[Composition-property correlations are fundamental to understand cement-based materials behavior and optimize their formulation. Modelling based on fundamental material component constitutes a reliable tool to establish these correlations with the advantage of better exploring formulation space when compared with the often adopted experimental trial-and-error approaches. In this context, Machine Learning (ML) and Micromechanics-Based (MB) methods have been concurrently used for property prediction from material composition. Here, we show that these techniques can be allies for establishing composition-property correlations. We focus on predictions of Ordinary Portland Cement pastes elastic properties, but the outlined strategy can be extended to other cement systems. Various microstructures representations are considered in MB estimates, including multiscale representations and representations with ellipsoidal inclusions. In contrast, ML predictions do not need any a priori assumption on material microstructure. Predictions using ML and MB yield similar accuracy when compared against test datasets (but ML performed much better regarding the error estimated in training datasets). Working as allies, ML can be deployed to evaluate the (lack of) knowledge over the multi-dimensional parametric domains, and micromechanics provides a theoretical background for property data curation and is a tool to make up for missing data in databases.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>A probabilistic model for fast-to-evaluate 2D crack path prediction in heterogeneous materials</title>
      <description><![CDATA[This paper is devoted to the construction of a new fast-to-evaluate model for the prediction of 2D crack paths in concrete-like microstructures. The model generates piecewise linear cracks paths with segmentation points selected using a Markov chain model. The Markov chain kernel involves local indicators of mechanical interest and its parameters are learnt from numerical full-field 2D simulations of cracking using a cohesive-volumetric finite element solver called XPER. This model does not include any mechanical elements. It is the database, derived from the XPER crack, that contains the mechanical information and optimizes the probabilistic model. The resulting model exhibits a drastic improvement of CPU time in comparison to simulations from XPER.]]></description>
      <pubDate>Wed, 11 Jan 2023 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.8322</link>
      <guid>https://doi.org/10.46298/jtcam.8322</guid>
      <author>Pele, Kathleen</author>
      <author>Baccou, Jean</author>
      <author>Daridon, Loïc</author>
      <author>Liandrat, Jacques</author>
      <author>Le Gouic, Thibaut</author>
      <author>Monerie, Yann</author>
      <author>Péralès, Frédéric</author>
      <dc:creator>Pele, Kathleen</dc:creator>
      <dc:creator>Baccou, Jean</dc:creator>
      <dc:creator>Daridon, Loïc</dc:creator>
      <dc:creator>Liandrat, Jacques</dc:creator>
      <dc:creator>Le Gouic, Thibaut</dc:creator>
      <dc:creator>Monerie, Yann</dc:creator>
      <dc:creator>Péralès, Frédéric</dc:creator>
      <content:encoded><![CDATA[This paper is devoted to the construction of a new fast-to-evaluate model for the prediction of 2D crack paths in concrete-like microstructures. The model generates piecewise linear cracks paths with segmentation points selected using a Markov chain model. The Markov chain kernel involves local indicators of mechanical interest and its parameters are learnt from numerical full-field 2D simulations of cracking using a cohesive-volumetric finite element solver called XPER. This model does not include any mechanical elements. It is the database, derived from the XPER crack, that contains the mechanical information and optimizes the probabilistic model. The resulting model exhibits a drastic improvement of CPU time in comparison to simulations from XPER.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Efficient Update of Redundancy Matrices for Truss and Frame Structures</title>
      <description><![CDATA[Redundancy matrices provide insights into the load carrying behavior of statically indeterminate structures. This information can be employed for the design and analysis of structures with regard to certain objectives, for example reliability, robustness, or adaptability. In this context, the structure is often iteratively examined with the help of slight adjustments. However, this procedure generally requires a high computational effort for the recalculation of the redundancy matrix due to the necessity of costly matrix operations. This paper addresses this problem by providing generic algebraic formulations for efficiently updating the redundancy matrix (and related matrices). The formulations include various modifications like adding, removing, and exchanging elements and are applicable to truss and frame structures. With several examples, we demonstrate the interaction between the formulas and their mechanical interpretation. Finally, a performance test for a scaleable structure is presented.]]></description>
      <pubDate>Thu, 10 Nov 2022 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.9615</link>
      <guid>https://doi.org/10.46298/jtcam.9615</guid>
      <author>Krake, Tim</author>
      <author>von Scheven, Malte</author>
      <author>Gade, Jan</author>
      <author>Abdelaal, Moataz</author>
      <author>Weiskopf, Daniel</author>
      <author>Bischoff, Manfred</author>
      <dc:creator>Krake, Tim</dc:creator>
      <dc:creator>von Scheven, Malte</dc:creator>
      <dc:creator>Gade, Jan</dc:creator>
      <dc:creator>Abdelaal, Moataz</dc:creator>
      <dc:creator>Weiskopf, Daniel</dc:creator>
      <dc:creator>Bischoff, Manfred</dc:creator>
      <content:encoded><![CDATA[Redundancy matrices provide insights into the load carrying behavior of statically indeterminate structures. This information can be employed for the design and analysis of structures with regard to certain objectives, for example reliability, robustness, or adaptability. In this context, the structure is often iteratively examined with the help of slight adjustments. However, this procedure generally requires a high computational effort for the recalculation of the redundancy matrix due to the necessity of costly matrix operations. This paper addresses this problem by providing generic algebraic formulations for efficiently updating the redundancy matrix (and related matrices). The formulations include various modifications like adding, removing, and exchanging elements and are applicable to truss and frame structures. With several examples, we demonstrate the interaction between the formulas and their mechanical interpretation. Finally, a performance test for a scaleable structure is presented.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Photometric DIC: a unified framework for global Stereo Digital Image Correlation based on the construction of textured digital twins</title>
      <description><![CDATA[An innovative approach allowing to rigorously address surface curvature and lighting effects in Digital Image Correlation (DIC) is proposed. We draw inspiration from the research work in Computer Vision (CV) regarding the physical modelling of a camera and adopt it to bring novel and significant capabilities for full-field measurements in experimental solid mechanics. It gives rise to a unified framework for global stereo DIC that we call Photometric DIC (PhDIC). It is based on the irradiance equation that relies on physical considerations and explicit assumptions, which stands for a clear breakthrough compared to the usual grey level conservation assumption. Most importantly, it allows to define a Digital Twin of the Region of Interest, which makes it possible to compare a model with different observations (real images taken from different viewpoints). This results in a consistent formalism throughout the framework, suitable for large-deformation and large-strain displacement measurements. The potential of PhDIC is illustrated on a real case. Multi-view images are first used to measure (or scan) the shape and albedo (sometimes called intrinsic texture) of an open-hole plate. The kinematic basis considered for the displacement measurement is associated to a Finite-Element mesh. Results for the shape and albedo measurement are compared for two completely different sets of pictures. Eventually, a large displacement of the structure is measured using a well-chosen single image.]]></description>
      <pubDate>Tue, 30 Aug 2022 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7467</link>
      <guid>https://doi.org/10.46298/jtcam.7467</guid>
      <author>Fouque, Raphaël</author>
      <author>Bouclier, Robin</author>
      <author>Passieux, Jean-Charles</author>
      <author>Périé, Jean-Noël</author>
      <dc:creator>Fouque, Raphaël</dc:creator>
      <dc:creator>Bouclier, Robin</dc:creator>
      <dc:creator>Passieux, Jean-Charles</dc:creator>
      <dc:creator>Périé, Jean-Noël</dc:creator>
      <content:encoded><![CDATA[An innovative approach allowing to rigorously address surface curvature and lighting effects in Digital Image Correlation (DIC) is proposed. We draw inspiration from the research work in Computer Vision (CV) regarding the physical modelling of a camera and adopt it to bring novel and significant capabilities for full-field measurements in experimental solid mechanics. It gives rise to a unified framework for global stereo DIC that we call Photometric DIC (PhDIC). It is based on the irradiance equation that relies on physical considerations and explicit assumptions, which stands for a clear breakthrough compared to the usual grey level conservation assumption. Most importantly, it allows to define a Digital Twin of the Region of Interest, which makes it possible to compare a model with different observations (real images taken from different viewpoints). This results in a consistent formalism throughout the framework, suitable for large-deformation and large-strain displacement measurements. The potential of PhDIC is illustrated on a real case. Multi-view images are first used to measure (or scan) the shape and albedo (sometimes called intrinsic texture) of an open-hole plate. The kinematic basis considered for the displacement measurement is associated to a Finite-Element mesh. Results for the shape and albedo measurement are compared for two completely different sets of pictures. Eventually, a large displacement of the structure is measured using a well-chosen single image.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Effects of the microstructural uncertainties on the poroelastic and the diffusive properties of mortar</title>
      <description><![CDATA[The assessment of the durability of civil engineering structures subjected to several chemical attacks requires the development of chemo-poromechanical models. The mechanical and chemical degradations depend on several factors such as the initial composition of the porous medium. A multi-scale model is used to incorporate the multi-level microstructural properties of the mortar material. The present paper aims to study the effect of morphological and local material properties uncertainties on the poroelastic and diffusive properties of mortar estimated with the help of analytical homogenization. At first, the proposed model is validated for different cement paste and mortar by comparison to experimental results and micromechanical models. Secondly, based on a literature study, sensitivity and uncertainty analysis have been developed to assess the stochastic predictions of the multi-scale model. The main result highlights the predominant impact of the cement matrix phases (C-S-H) and interfacial transition area at the mortar scale. Furthermore, the sensitive analysis underlines that the material properties induce more variability than the volume fraction.]]></description>
      <pubDate>Sun, 19 Jun 2022 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.8849</link>
      <guid>https://doi.org/10.46298/jtcam.8849</guid>
      <author>Socié, Adrien</author>
      <author>Monerie, Yann</author>
      <author>Péralès, Frédéric</author>
      <dc:creator>Socié, Adrien</dc:creator>
      <dc:creator>Monerie, Yann</dc:creator>
      <dc:creator>Péralès, Frédéric</dc:creator>
      <content:encoded><![CDATA[The assessment of the durability of civil engineering structures subjected to several chemical attacks requires the development of chemo-poromechanical models. The mechanical and chemical degradations depend on several factors such as the initial composition of the porous medium. A multi-scale model is used to incorporate the multi-level microstructural properties of the mortar material. The present paper aims to study the effect of morphological and local material properties uncertainties on the poroelastic and diffusive properties of mortar estimated with the help of analytical homogenization. At first, the proposed model is validated for different cement paste and mortar by comparison to experimental results and micromechanical models. Secondly, based on a literature study, sensitivity and uncertainty analysis have been developed to assess the stochastic predictions of the multi-scale model. The main result highlights the predominant impact of the cement matrix phases (C-S-H) and interfacial transition area at the mortar scale. Furthermore, the sensitive analysis underlines that the material properties induce more variability than the volume fraction.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>A simple extension of FFT-based methods to strain gradient loadings - Application to the homogenization of beams and plates with linear and non-linear behaviors</title>
      <description><![CDATA[Because of their simplicity, efficiency and ability for parallelism, FFT-based methods are very attractive in the context of numerical periodic homogenization, especially when compared to standard FE codes used in the same context. They allow applying to a unit-cell a uniform average strain with a periodic strain fluctuation that is an unknown quantity. Solving the problem allows to evaluate the complete stress-strain fields. The present work proposes to extend the use of the method from uniform loadings (i.e. uniform applied strain) to strain gradient loadings (i.e. strain fields with a uniform strain gradient) while keeping the algorithm as simple as possible. The identification of a subset of strain gradient loadings allows for a minimally invasive modification of the iterative algorithm so that the implementation is straightforward. In spite of a reduced subset of 9 independent loadings among the 18 available, the second part of the paper demonstrates that it is enough for considering the homogenization of beams and plates. A first application validates the approach and compares it to another FFT-based method dedicated to the homogenization of plates. The second application concerns the homogenization of beams, for the first time considered (to author's knowledge) with an FFT-based solver. The method applies to different beam cross-sections and the proposition of using composite voxels drastically improves the numerical solution when the beam cross-section is not conform with the spatial discretization, especially for torsion loading. As a result, the massively parallel AMITEX_FFTP code has been slightly modified and now offers a new functionality, allowing the users to prescribe torsions and flexions to beam or plate heterogeneous unit-cells.]]></description>
      <pubDate>Wed, 15 Jun 2022 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.6790</link>
      <guid>https://doi.org/10.46298/jtcam.6790</guid>
      <author>Gélébart, Lionel</author>
      <dc:creator>Gélébart, Lionel</dc:creator>
      <content:encoded><![CDATA[Because of their simplicity, efficiency and ability for parallelism, FFT-based methods are very attractive in the context of numerical periodic homogenization, especially when compared to standard FE codes used in the same context. They allow applying to a unit-cell a uniform average strain with a periodic strain fluctuation that is an unknown quantity. Solving the problem allows to evaluate the complete stress-strain fields. The present work proposes to extend the use of the method from uniform loadings (i.e. uniform applied strain) to strain gradient loadings (i.e. strain fields with a uniform strain gradient) while keeping the algorithm as simple as possible. The identification of a subset of strain gradient loadings allows for a minimally invasive modification of the iterative algorithm so that the implementation is straightforward. In spite of a reduced subset of 9 independent loadings among the 18 available, the second part of the paper demonstrates that it is enough for considering the homogenization of beams and plates. A first application validates the approach and compares it to another FFT-based method dedicated to the homogenization of plates. The second application concerns the homogenization of beams, for the first time considered (to author's knowledge) with an FFT-based solver. The method applies to different beam cross-sections and the proposition of using composite voxels drastically improves the numerical solution when the beam cross-section is not conform with the spatial discretization, especially for torsion loading. As a result, the massively parallel AMITEX_FFTP code has been slightly modified and now offers a new functionality, allowing the users to prescribe torsions and flexions to beam or plate heterogeneous unit-cells.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Rate dependency and ply thickness influence on transverse cracking evolution in cross-ply laminates</title>
      <description><![CDATA[In this study, the rate dependency of transverse cracking evolution in cross-ply laminates is investigated for several 90° plies thicknesses. The crack detection methodology is based on a recently proposed protocol relying on the use of infrared thermography. A new analysis methodology is proposed to make it more robust and to directly link the spatial localization of the crack with the stress level at which it occurs. Based on this methodology, the results obtained for various loading rates and 90° ply thicknesses are analysed. The crack density evolution with respect to stress apply to the laminate exhibits a rate dependency only for the [0/90]s configuration. This rate dependency is finally discussed based on transverse crack onset theories in cross-ply laminates.]]></description>
      <pubDate>Wed, 04 May 2022 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7062</link>
      <guid>https://doi.org/10.46298/jtcam.7062</guid>
      <author>Coussa, Fabien</author>
      <author>Berthe, Julien</author>
      <author>Ragonet, Matthieu</author>
      <dc:creator>Coussa, Fabien</dc:creator>
      <dc:creator>Berthe, Julien</dc:creator>
      <dc:creator>Ragonet, Matthieu</dc:creator>
      <content:encoded><![CDATA[In this study, the rate dependency of transverse cracking evolution in cross-ply laminates is investigated for several 90° plies thicknesses. The crack detection methodology is based on a recently proposed protocol relying on the use of infrared thermography. A new analysis methodology is proposed to make it more robust and to directly link the spatial localization of the crack with the stress level at which it occurs. Based on this methodology, the results obtained for various loading rates and 90° ply thicknesses are analysed. The crack density evolution with respect to stress apply to the laminate exhibits a rate dependency only for the [0/90]s configuration. This rate dependency is finally discussed based on transverse crack onset theories in cross-ply laminates.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>An examination of local strain fields evolution in ductile cast iron through micromechanical simulations based on 3D imaging</title>
      <description><![CDATA[Microscopic digital volume correlation (DVC) and finite element precoalescence strain evaluations are compared for two nodular cast iron specimens. Displacement fields from \textit{in-situ} 3D synchrotron laminography images are obtained by DVC. Subsequently the microstructure is explicitely meshed from the images considering nodules as voids. Boundary conditions are applied from the DVC measurement. Image segmentation-related uncertainties are taken into account and observed to be negligible with respect to the differences between strain levels. Macroscopic as well as local strain levels in coalescing ligaments between voids nucleated at large graphite nodules are compared. Macroscopic strain levels are consistently predicted. A very good agreement is observed for one of the specimens, while the strain levels for the second specimen presents some discrepancies. Limitations of the modeling and numerical framework are discussed in light of these differences. A discussion of the use of strain as coalescence indicator is initiated.]]></description>
      <pubDate>Thu, 07 Apr 2022 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7501</link>
      <guid>https://doi.org/10.46298/jtcam.7501</guid>
      <author>Navas, Victor Manuel Trejo</author>
      <author>Buljac, Ante</author>
      <author>Hild, François</author>
      <author>Morgeneyer, Thilo F.</author>
      <author>Bernacki, Marc</author>
      <author>Bouchard, Pierre-Olivier</author>
      <dc:creator>Navas, Victor Manuel Trejo</dc:creator>
      <dc:creator>Buljac, Ante</dc:creator>
      <dc:creator>Hild, François</dc:creator>
      <dc:creator>Morgeneyer, Thilo F.</dc:creator>
      <dc:creator>Bernacki, Marc</dc:creator>
      <dc:creator>Bouchard, Pierre-Olivier</dc:creator>
      <content:encoded><![CDATA[Microscopic digital volume correlation (DVC) and finite element precoalescence strain evaluations are compared for two nodular cast iron specimens. Displacement fields from \textit{in-situ} 3D synchrotron laminography images are obtained by DVC. Subsequently the microstructure is explicitely meshed from the images considering nodules as voids. Boundary conditions are applied from the DVC measurement. Image segmentation-related uncertainties are taken into account and observed to be negligible with respect to the differences between strain levels. Macroscopic as well as local strain levels in coalescing ligaments between voids nucleated at large graphite nodules are compared. Macroscopic strain levels are consistently predicted. A very good agreement is observed for one of the specimens, while the strain levels for the second specimen presents some discrepancies. Limitations of the modeling and numerical framework are discussed in light of these differences. A discussion of the use of strain as coalescence indicator is initiated.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Stress partitioning and effective behavior of N-phase laminates in anisotropic elasticity from a fast explicit method</title>
      <description><![CDATA[In this work, a fast explicit method, easy to implement numerically, is proposed in order to compute the effective behavior and the distribution of stresses in a general N-phase laminate made of parallel, planar and perfectly bonded interfaces. The solutions are exact for a homogeneous far-field loading and work for an arbitrary number of phases, a general linear anisotropic elasticity, as well as different uniform thermal and plastic strains in the phases. A simple direct analytical formula is also derived to compute the stress in a given phase once the effective behavior of the laminate is known. Moreover, the correctness of the proposed method is checked by comparisons with finite element simulation results on a same boundary value problem, showing excellent agreements. An application of the method is performed for a near-β titanium alloy with elongated grains, by comparing the level of internal stresses for different elastic loadings within a N-phase laminate made of 100,000 orientations and a 2-phase laminate of equal volume fraction with maximal elastic contrast. Interestingly, the maximum von Mises stress of the 2-phase laminate is always the lowest, which is explained by a volume fraction effect. Finally, comparisons with elastic self-consistent models considering oblate spheroidal grains of different aspect ratios are performed.]]></description>
      <pubDate>Tue, 29 Mar 2022 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.8506</link>
      <guid>https://doi.org/10.46298/jtcam.8506</guid>
      <author>Richeton, Thiebaud</author>
      <dc:creator>Richeton, Thiebaud</dc:creator>
      <content:encoded><![CDATA[In this work, a fast explicit method, easy to implement numerically, is proposed in order to compute the effective behavior and the distribution of stresses in a general N-phase laminate made of parallel, planar and perfectly bonded interfaces. The solutions are exact for a homogeneous far-field loading and work for an arbitrary number of phases, a general linear anisotropic elasticity, as well as different uniform thermal and plastic strains in the phases. A simple direct analytical formula is also derived to compute the stress in a given phase once the effective behavior of the laminate is known. Moreover, the correctness of the proposed method is checked by comparisons with finite element simulation results on a same boundary value problem, showing excellent agreements. An application of the method is performed for a near-β titanium alloy with elongated grains, by comparing the level of internal stresses for different elastic loadings within a N-phase laminate made of 100,000 orientations and a 2-phase laminate of equal volume fraction with maximal elastic contrast. Interestingly, the maximum von Mises stress of the 2-phase laminate is always the lowest, which is explained by a volume fraction effect. Finally, comparisons with elastic self-consistent models considering oblate spheroidal grains of different aspect ratios are performed.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>A non-local model for the description of twinning in polycrystalline materials in the context of infinitesimal strains: application to a magnesium alloy</title>
      <description><![CDATA[A polycrystalline plasticity model, which incorporates the contribution of deformation twinning, is proposed. For this purpose, each material point is treated as a composite material consisting of a parent constituent and multiple twin variants. In the constitutive equations, the twin volume fractions and their spatial gradients are treated as external state variables to account for the contribution of twin boundaries to free energy. The set of constitutive relations is implemented in a spectral solver, which allows solving the differential equations resulting from equilibrium and compatibility conditions. The proposed model is then used to investigate the behavior of a AZ31 magnesium alloy. For the investigated loading conditions, the mechanical behavior is controlled by the joint contribution of basal slip and tensile twinning. Also, according to the numerical results, the development of crystallographic texture, morphological texture and internal stresses is consistent with the experimental observations of the literature.]]></description>
      <pubDate>Sun, 06 Mar 2022 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7562</link>
      <guid>https://doi.org/10.46298/jtcam.7562</guid>
      <author>Mareau, Charles</author>
      <author>Abdolvand, Hamidreza</author>
      <dc:creator>Mareau, Charles</dc:creator>
      <dc:creator>Abdolvand, Hamidreza</dc:creator>
      <content:encoded><![CDATA[A polycrystalline plasticity model, which incorporates the contribution of deformation twinning, is proposed. For this purpose, each material point is treated as a composite material consisting of a parent constituent and multiple twin variants. In the constitutive equations, the twin volume fractions and their spatial gradients are treated as external state variables to account for the contribution of twin boundaries to free energy. The set of constitutive relations is implemented in a spectral solver, which allows solving the differential equations resulting from equilibrium and compatibility conditions. The proposed model is then used to investigate the behavior of a AZ31 magnesium alloy. For the investigated loading conditions, the mechanical behavior is controlled by the joint contribution of basal slip and tensile twinning. Also, according to the numerical results, the development of crystallographic texture, morphological texture and internal stresses is consistent with the experimental observations of the literature.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>A damage criterion based on energy balance for isotropic cohesive zone model</title>
      <description><![CDATA[The objective of this paper is to present an energy damage criterion for cohesive zone models (CZM) within the framework of the non-linear thermodynamics of irreversible processes (TIP). An isotropic elastic damageable material is considered for isothermal transformations. Damage is then the only irreversible effect accompanying the deformation process and this mechanism is supposed to be fully dissipative. Once a separation law and a damage state variable have been chosen, the paper shows that the damage criterion can be automatically derived from the energy balance. From this observation, a CZM is derived for a given choice of traction-separation law and damage state variable and the quality of its numerical predictions is analyzed using an experimental benchmark bending test extracted from literature. Finally, damage, elastic and dissipated energy fields around the crack path are shown during this rupture test.</br></br>Evolution of the dissipated energy field.</br><img src="https://hal.archives-ouvertes.fr/hal-03098095v4/file/animation.gif" style="height:8cm;"></br></br>]]></description>
      <pubDate>Sun, 06 Mar 2022 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7056</link>
      <guid>https://doi.org/10.46298/jtcam.7056</guid>
      <author>Chrysochoos, André</author>
      <author>Daridon, Loïc</author>
      <author>Renouf, Mathieu</author>
      <dc:creator>Chrysochoos, André</dc:creator>
      <dc:creator>Daridon, Loïc</dc:creator>
      <dc:creator>Renouf, Mathieu</dc:creator>
      <content:encoded><![CDATA[The objective of this paper is to present an energy damage criterion for cohesive zone models (CZM) within the framework of the non-linear thermodynamics of irreversible processes (TIP). An isotropic elastic damageable material is considered for isothermal transformations. Damage is then the only irreversible effect accompanying the deformation process and this mechanism is supposed to be fully dissipative. Once a separation law and a damage state variable have been chosen, the paper shows that the damage criterion can be automatically derived from the energy balance. From this observation, a CZM is derived for a given choice of traction-separation law and damage state variable and the quality of its numerical predictions is analyzed using an experimental benchmark bending test extracted from literature. Finally, damage, elastic and dissipated energy fields around the crack path are shown during this rupture test.</br></br>Evolution of the dissipated energy field.</br><img src="https://hal.archives-ouvertes.fr/hal-03098095v4/file/animation.gif" style="height:8cm;"></br></br>]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>A computational homogenization framework with enhanced localization criterion for macroscopic cohesive failure in heterogeneous materials</title>
      <description><![CDATA[Computational homogenization allows to let the macroscopic constitutive behavior of materials emerge from microscale simulations without loss of generality with respect to microstructure and microscale constitutive response. Although computationally demanding, computational homogenization works very well for the hardening response of materials where the macroscopic stress and strain fields are smooth. However, in case of softening materials, when localization of deformation takes place, special care is needed to ensure objectivity of the method. In this paper, a generic multiscale computational homogenization approach for modeling onset and propagation of cracks in heterogeneous materials that is capable of considering various microscale mechanisms is presented. The common acoustic tensor bifurcation criterion is reinforced by an additional condition to help detect the localization mode more robustly. After the onset of macroscale localization, a key scale transition parameter is needed to translate the macroscopic displacement jump to an averaged strain over the micromodel domain. Then the macroscale crack is governed by a homogenized traction-separation relation evaluated from the underlying micromodel in which micro-failure accumulates. The scale transition parameter is studied for a range of different scenarios and endowed with a geometrical interpretation. Various numerical tests have been performed to confirm the objectivity and validity of the framework. The framework is generic in the sense that no assumptions on the microscale constitutive or kinematic representation of material failure are made in the scale transition. The framework is also highly compatible with the first order computational homogenization, which minimizes the additional complexity of adding macroscopic crack growth to the computational implementation.]]></description>
      <pubDate>Sun, 27 Feb 2022 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7707</link>
      <guid>https://doi.org/10.46298/jtcam.7707</guid>
      <author>Ke, Lu</author>
      <author>van Der Meer, Frans, P</author>
      <dc:creator>Ke, Lu</dc:creator>
      <dc:creator>van Der Meer, Frans, P</dc:creator>
      <content:encoded><![CDATA[Computational homogenization allows to let the macroscopic constitutive behavior of materials emerge from microscale simulations without loss of generality with respect to microstructure and microscale constitutive response. Although computationally demanding, computational homogenization works very well for the hardening response of materials where the macroscopic stress and strain fields are smooth. However, in case of softening materials, when localization of deformation takes place, special care is needed to ensure objectivity of the method. In this paper, a generic multiscale computational homogenization approach for modeling onset and propagation of cracks in heterogeneous materials that is capable of considering various microscale mechanisms is presented. The common acoustic tensor bifurcation criterion is reinforced by an additional condition to help detect the localization mode more robustly. After the onset of macroscale localization, a key scale transition parameter is needed to translate the macroscopic displacement jump to an averaged strain over the micromodel domain. Then the macroscale crack is governed by a homogenized traction-separation relation evaluated from the underlying micromodel in which micro-failure accumulates. The scale transition parameter is studied for a range of different scenarios and endowed with a geometrical interpretation. Various numerical tests have been performed to confirm the objectivity and validity of the framework. The framework is generic in the sense that no assumptions on the microscale constitutive or kinematic representation of material failure are made in the scale transition. The framework is also highly compatible with the first order computational homogenization, which minimizes the additional complexity of adding macroscopic crack growth to the computational implementation.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>The irreversible thermal expansion of an energetic material</title>
      <description><![CDATA[The work deals with a macroscopically isotropic energetic material based on triamino-trinitrobenzene (TATB) crystals bonded with a small volume fraction of a thermoplastic polymer. This material is shown experimentally to display an irreversible thermal expansion behavior characterized by dilatancy and variations of its thermal expansion coefficient when heated or cooled outside a narrow reversibility temperature range. The analysis of cooling results suggests the existence of residual stresses in the initial state, attributed to the manufacturing process. Microstructure-level FFT computations including the very strong anisotropic thermoelastic TATB crystal response and temperature-dependent binder plasticity, show that strong internal stresses develop in the disoriented crystals under thermal load, either heating or cooling. Upon cooling, binder plastic yielding in hindered, thus promoting essentially brittle microcracking, while it is favored upon heating. Despite its low volume fraction, the role of the binder is essential, its plastic yielding causing stress redistribution and residual stresses upon cooling back to ambient.]]></description>
      <pubDate>Wed, 17 Nov 2021 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7091</link>
      <guid>https://doi.org/10.46298/jtcam.7091</guid>
      <author>Trumel, Hervé</author>
      <author>Willot, François</author>
      <author>Peyres, Thomas</author>
      <author>Biessy, Maxime</author>
      <author>Rabette, François</author>
      <dc:creator>Trumel, Hervé</dc:creator>
      <dc:creator>Willot, François</dc:creator>
      <dc:creator>Peyres, Thomas</dc:creator>
      <dc:creator>Biessy, Maxime</dc:creator>
      <dc:creator>Rabette, François</dc:creator>
      <content:encoded><![CDATA[The work deals with a macroscopically isotropic energetic material based on triamino-trinitrobenzene (TATB) crystals bonded with a small volume fraction of a thermoplastic polymer. This material is shown experimentally to display an irreversible thermal expansion behavior characterized by dilatancy and variations of its thermal expansion coefficient when heated or cooled outside a narrow reversibility temperature range. The analysis of cooling results suggests the existence of residual stresses in the initial state, attributed to the manufacturing process. Microstructure-level FFT computations including the very strong anisotropic thermoelastic TATB crystal response and temperature-dependent binder plasticity, show that strong internal stresses develop in the disoriented crystals under thermal load, either heating or cooling. Upon cooling, binder plastic yielding in hindered, thus promoting essentially brittle microcracking, while it is favored upon heating. Despite its low volume fraction, the role of the binder is essential, its plastic yielding causing stress redistribution and residual stresses upon cooling back to ambient.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Residual strains estimation in the annulus fibrosus through digital image correlation</title>
      <description><![CDATA[Up-to-date, back pain is among the most prevalent health issues and generally takes its origins from lesions of the annulus fibrosus (AF). While the AF ex vivo mechanical properties are increasingly well understood, in vivo data are still missing. In particular, very few studies have precisely measured the residual strains within the AF and thus the in vivo deformation state of the AF is still miss-interpreted and miss-evaluated. In this work, we propose an original and robust method for the AF residual strains quantification via digital image correlation technics. Ten pig annulus fibrosus were extracted from adjacent vertebrae followed by a radial incision to release the residual strains. The operations were filmed and then analyzed by a custom digital image correlation software in order to quantify the circumferential, radial and shear residual deformations. Our results show that residual strains are of the same order of magnitude than the in vivo one. The average circumferential strains are in tension on the outer periphery ([3.32; 5.94]%) and in compression on the inner periphery ([−6.4; −1.69]%). The mean radial residual strains are essentially in compression ([−10.4; 2.29]%). Locally, radial and circumferential residual strains can reach really large values up to 40% of compression. The mean shear strains remain very small (−0.04% ± 2.88%). This study also shows that circumferential and radial residual strains evolve linearly along the radius and non-linearly along the angle. We propose a simple model to predict their spatial variations. Our results and methods will allow the quantification of more realistic in vivo strains and stresses within the human intervertebral disc.]]></description>
      <pubDate>Wed, 17 Nov 2021 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.6971</link>
      <guid>https://doi.org/10.46298/jtcam.6971</guid>
      <author>Dusfour, Gilles</author>
      <author>Ambard, Dominique</author>
      <author>Cañadas, Patrick</author>
      <author>Lefloch, Simon</author>
      <dc:creator>Dusfour, Gilles</dc:creator>
      <dc:creator>Ambard, Dominique</dc:creator>
      <dc:creator>Cañadas, Patrick</dc:creator>
      <dc:creator>Lefloch, Simon</dc:creator>
      <content:encoded><![CDATA[Up-to-date, back pain is among the most prevalent health issues and generally takes its origins from lesions of the annulus fibrosus (AF). While the AF ex vivo mechanical properties are increasingly well understood, in vivo data are still missing. In particular, very few studies have precisely measured the residual strains within the AF and thus the in vivo deformation state of the AF is still miss-interpreted and miss-evaluated. In this work, we propose an original and robust method for the AF residual strains quantification via digital image correlation technics. Ten pig annulus fibrosus were extracted from adjacent vertebrae followed by a radial incision to release the residual strains. The operations were filmed and then analyzed by a custom digital image correlation software in order to quantify the circumferential, radial and shear residual deformations. Our results show that residual strains are of the same order of magnitude than the in vivo one. The average circumferential strains are in tension on the outer periphery ([3.32; 5.94]%) and in compression on the inner periphery ([−6.4; −1.69]%). The mean radial residual strains are essentially in compression ([−10.4; 2.29]%). Locally, radial and circumferential residual strains can reach really large values up to 40% of compression. The mean shear strains remain very small (−0.04% ± 2.88%). This study also shows that circumferential and radial residual strains evolve linearly along the radius and non-linearly along the angle. We propose a simple model to predict their spatial variations. Our results and methods will allow the quantification of more realistic in vivo strains and stresses within the human intervertebral disc.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Passive discrete lens for broadband elastic guided wave focusing</title>
      <description><![CDATA[Elastic guided wave focusing is of great interest for applications such as vibroacoustic control, energy harvesting, or Structural Health Monitoring. Different strategies allow generation of this effect, GRadient-INdex devices in particular exploit medium with varying properties such as thickness to reproduce an adequate refractive index profile as in optics. The resulting continuous profiles have a curved geometry that can be hard to manufacture, and be difficult to integrate in a given design. The purpose of this paper is to propose a discrete design for a GRIN lens. It is composed of segments selected in number and thickness to give similar focusing effects as a continuous lens profile. The identified configuration is manufactured and bounded on an aluminium plate to evaluate the effective focusing performances. Numerical and experimental vibrometry results confirm that the proposed lens exhibits a fixed focal point over a broad frequency range. The discrete design overcomes fabrication issues encountered in continuous design, allowing for an easier integration in devices for elastic wave control.]]></description>
      <pubDate>Tue, 05 Oct 2021 19:53:20 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.6652</link>
      <guid>https://doi.org/10.46298/jtcam.6652</guid>
      <author>Sadoulet-Reboul, Emeline</author>
      <author>Matten, Gaël</author>
      <author>Yi, Kaijun</author>
      <author>Ouisse, Morvan</author>
      <dc:creator>Sadoulet-Reboul, Emeline</dc:creator>
      <dc:creator>Matten, Gaël</dc:creator>
      <dc:creator>Yi, Kaijun</dc:creator>
      <dc:creator>Ouisse, Morvan</dc:creator>
      <content:encoded><![CDATA[Elastic guided wave focusing is of great interest for applications such as vibroacoustic control, energy harvesting, or Structural Health Monitoring. Different strategies allow generation of this effect, GRadient-INdex devices in particular exploit medium with varying properties such as thickness to reproduce an adequate refractive index profile as in optics. The resulting continuous profiles have a curved geometry that can be hard to manufacture, and be difficult to integrate in a given design. The purpose of this paper is to propose a discrete design for a GRIN lens. It is composed of segments selected in number and thickness to give similar focusing effects as a continuous lens profile. The identified configuration is manufactured and bounded on an aluminium plate to evaluate the effective focusing performances. Numerical and experimental vibrometry results confirm that the proposed lens exhibits a fixed focal point over a broad frequency range. The discrete design overcomes fabrication issues encountered in continuous design, allowing for an easier integration in devices for elastic wave control.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Ductile crack initiation and growth on a plasticized Polyvinylchloride during air bag deployment</title>
      <description><![CDATA[With the goal of ensuring the security of passengers for automotive industry, the present work addresses the ductile fracture process of plasticized PVC. Dedicated clamped single edge notch bending (SENB) specimens were used to characterize the mechanisms of crack initiation and propagation for the studied material. The exploitation of the experimental database associated with finite element simulation of the crack propagation allowed, on the one hand, the calibration factor η<sub>p</sub> of this specific SENB specimen to be established, as a function of the crack depth ratio. On the other hand, the fracture toughness of the studied plasticized PVC was estimated to be 10.8 kJ/m<sup>2</sup>, value which was close to that reported in the literature for modified PVC. By using this fracture toughness value, a methodology aiming at the prediction of ductile crack initiation of the PVC skin integrated into a real dashboard (full scale test) was proposed.]]></description>
      <pubDate>Thu, 30 Sep 2021 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.7401</link>
      <guid>https://doi.org/10.46298/jtcam.7401</guid>
      <author>Laiarinandrasana, Lucien</author>
      <author>Bertaux, Clément</author>
      <author>Amouroux, Nicolas</author>
      <author>Ovalle Rodas, Cristian</author>
      <dc:creator>Laiarinandrasana, Lucien</dc:creator>
      <dc:creator>Bertaux, Clément</dc:creator>
      <dc:creator>Amouroux, Nicolas</dc:creator>
      <dc:creator>Ovalle Rodas, Cristian</dc:creator>
      <content:encoded><![CDATA[With the goal of ensuring the security of passengers for automotive industry, the present work addresses the ductile fracture process of plasticized PVC. Dedicated clamped single edge notch bending (SENB) specimens were used to characterize the mechanisms of crack initiation and propagation for the studied material. The exploitation of the experimental database associated with finite element simulation of the crack propagation allowed, on the one hand, the calibration factor η<sub>p</sub> of this specific SENB specimen to be established, as a function of the crack depth ratio. On the other hand, the fracture toughness of the studied plasticized PVC was estimated to be 10.8 kJ/m<sup>2</sup>, value which was close to that reported in the literature for modified PVC. By using this fracture toughness value, a methodology aiming at the prediction of ductile crack initiation of the PVC skin integrated into a real dashboard (full scale test) was proposed.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>An effective parameterization of texture-induced viscous anisotropy in orthotropic materials with application for modeling geodynamical flows</title>
      <description><![CDATA[In this article, we describe the mathematical formulation and the numerical implementation of an effective parametrization of the viscous anisotropy of orthorhombic materials produced by crystallographic preferred orientations (CPO or texture), which can be integrated into 3D geodynamic and materials science codes. Here, the approach is applied to characterize the texture-induced viscous anisotropy of olivine polycrystals, the main constituent of the Earth's upper mantle. The parameterization is based on the Hill (1948) orthotropic yield criterion. The coefficients of the Hill yield surface are calibrated based on numerical tests performed using the second order Viscoplastic Self-consistent (SO-VPSC) model. The parametrization was implemented in a 3D thermo-mechanical finite-element code developed to model large-scale geodynamical flows, in the form of a Maxwell rheology combining isotropic elastic and anisotropic non-linear viscous behaviors. The implementation was validated by comparison with results of the analytical solution and of the SO-VPSC model for simple shear and axial compression of a homogeneous anisotropic material. An application designed to examine the effect of texture-induced viscous anisotropy on the reactivation of mantle shear zones in continental plates highlights unexpected couplings between localized deformation controlled by variations in the orientation and intensity of the olivine texture in the mantle and the mechanical behavior of the elasto-viscoplastic overlying crust. Importantly, the computational time only increases by a factor 2-3 with respect to the classic isotropic Maxwell viscoelastic rheology.]]></description>
      <pubDate>Mon, 12 Jul 2021 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.6737</link>
      <guid>https://doi.org/10.46298/jtcam.6737</guid>
      <author>Signorelli, Javier</author>
      <author>Hassani, Riad</author>
      <author>Tommasi, Andréa</author>
      <author>Mameri, Lucan</author>
      <dc:creator>Signorelli, Javier</dc:creator>
      <dc:creator>Hassani, Riad</dc:creator>
      <dc:creator>Tommasi, Andréa</dc:creator>
      <dc:creator>Mameri, Lucan</dc:creator>
      <content:encoded><![CDATA[In this article, we describe the mathematical formulation and the numerical implementation of an effective parametrization of the viscous anisotropy of orthorhombic materials produced by crystallographic preferred orientations (CPO or texture), which can be integrated into 3D geodynamic and materials science codes. Here, the approach is applied to characterize the texture-induced viscous anisotropy of olivine polycrystals, the main constituent of the Earth's upper mantle. The parameterization is based on the Hill (1948) orthotropic yield criterion. The coefficients of the Hill yield surface are calibrated based on numerical tests performed using the second order Viscoplastic Self-consistent (SO-VPSC) model. The parametrization was implemented in a 3D thermo-mechanical finite-element code developed to model large-scale geodynamical flows, in the form of a Maxwell rheology combining isotropic elastic and anisotropic non-linear viscous behaviors. The implementation was validated by comparison with results of the analytical solution and of the SO-VPSC model for simple shear and axial compression of a homogeneous anisotropic material. An application designed to examine the effect of texture-induced viscous anisotropy on the reactivation of mantle shear zones in continental plates highlights unexpected couplings between localized deformation controlled by variations in the orientation and intensity of the olivine texture in the mantle and the mechanical behavior of the elasto-viscoplastic overlying crust. Importantly, the computational time only increases by a factor 2-3 with respect to the classic isotropic Maxwell viscoelastic rheology.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Non steady-state intersonic cracks in elastomer membranes under large static strain</title>
      <description><![CDATA[Dynamic crack propagation in elastomer membranes is investigated; the focus is laid on cracks reaching the speed of shear waves in the material. The specific experimental setup developed to measure crack speed is presented in details. The protocol consists in (1) stretching an elastomer membrane under planar tension loading conditions, then (2) initiating a small crack on one side of the membrane. The crack speed is measured all along the crack path in both reference and actual configurations, including both acceleration and deceleration phases, i.e. non steady-state crack propagation phases. The influence of the prescribed stretch ratio on crack speed is analysed in the light of both these new experiments and the few previously published studies. Conclusions previously drawn for steady-state crack growth are extended to non steady-state conditions: stretch perpendicular to the crack path governs crack speed in intersonic crack propagation regime, and the role of the stretch in crack direction is minor.]]></description>
      <pubDate>Wed, 26 May 2021 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.6906</link>
      <guid>https://doi.org/10.46298/jtcam.6906</guid>
      <author>Corre, Thomas</author>
      <author>Coret, Michel</author>
      <author>Verron, Erwan</author>
      <author>Leblé, Bruno</author>
      <dc:creator>Corre, Thomas</dc:creator>
      <dc:creator>Coret, Michel</dc:creator>
      <dc:creator>Verron, Erwan</dc:creator>
      <dc:creator>Leblé, Bruno</dc:creator>
      <content:encoded><![CDATA[Dynamic crack propagation in elastomer membranes is investigated; the focus is laid on cracks reaching the speed of shear waves in the material. The specific experimental setup developed to measure crack speed is presented in details. The protocol consists in (1) stretching an elastomer membrane under planar tension loading conditions, then (2) initiating a small crack on one side of the membrane. The crack speed is measured all along the crack path in both reference and actual configurations, including both acceleration and deceleration phases, i.e. non steady-state crack propagation phases. The influence of the prescribed stretch ratio on crack speed is analysed in the light of both these new experiments and the few previously published studies. Conclusions previously drawn for steady-state crack growth are extended to non steady-state conditions: stretch perpendicular to the crack path governs crack speed in intersonic crack propagation regime, and the role of the stretch in crack direction is minor.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Comparison of the Von Kármán and Kirchhoff models for the post-buckling and vibrations of elastic beams</title>
      <description><![CDATA[We compare different models describing the buckling, post-buckling and vibrations of elastic beams in the plane. Focus is put on the first buckled equilibrium solution and the first two vibration modes around it. In the incipient post-buckling regime, the classic Woinowsky-Krieger model is known to grasp the behavior of the system. It is based on the von Kármán approximation, a 2nd order expansion in the strains of the buckled beam. But as the curvature of the beam becomes larger, the Woinowsky-Krieger model starts to show limitations and we introduce a 3rd order model, derived from the geometrically-exact Kirchhoff model. We discuss and quantify the shortcomings of the Woinowsky-Krieger model and the contributions of the 3rd order terms in the new model, and we compare them both to the Kirchhoff model. Different ways to nondi-mensionalize the models are compared and we believe that, although this study is performed for specific boundary conditions, the present results have a general scope and can be used as abacuses to estimate the validity range of the simplified models.]]></description>
      <pubDate>Sun, 16 May 2021 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.6828</link>
      <guid>https://doi.org/10.46298/jtcam.6828</guid>
      <author>Neukirch, Sébastien</author>
      <author>Yavari, Morteza</author>
      <author>Challamel, Noël</author>
      <author>Thomas, Olivier</author>
      <dc:creator>Neukirch, Sébastien</dc:creator>
      <dc:creator>Yavari, Morteza</dc:creator>
      <dc:creator>Challamel, Noël</dc:creator>
      <dc:creator>Thomas, Olivier</dc:creator>
      <content:encoded><![CDATA[We compare different models describing the buckling, post-buckling and vibrations of elastic beams in the plane. Focus is put on the first buckled equilibrium solution and the first two vibration modes around it. In the incipient post-buckling regime, the classic Woinowsky-Krieger model is known to grasp the behavior of the system. It is based on the von Kármán approximation, a 2nd order expansion in the strains of the buckled beam. But as the curvature of the beam becomes larger, the Woinowsky-Krieger model starts to show limitations and we introduce a 3rd order model, derived from the geometrically-exact Kirchhoff model. We discuss and quantify the shortcomings of the Woinowsky-Krieger model and the contributions of the 3rd order terms in the new model, and we compare them both to the Kirchhoff model. Different ways to nondi-mensionalize the models are compared and we believe that, although this study is performed for specific boundary conditions, the present results have a general scope and can be used as abacuses to estimate the validity range of the simplified models.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>An FFT solver used for virtual Dynamic Mechanical Analysis experiments: Application to a glassy/amorphous system and to a particulate composite</title>
      <description><![CDATA[FFT-based solvers are increasingly used by many researcher groups interested in modelling the mechanical behavior associated to a heterogeneous microstructure. A development is reported here that concerns the viscoelastic behavior of composite structures generally studied experimentally through Dynamic Mechanical Analysis (DMA). A parallelized computation code developed with complex-valued quantities provides virtual DMA experiments directly in the frequency domain on a heterogeneous system described by a voxel grid of mechanical properties. The achieved precision and computation times are very good. An effort has been made to illustrate the application of such a virtual DMA tool through two examples from the literature: the modelling of glassy/amorphous systems at a small scale and the modelling of experimental data obtained in temperature sweeping mode by DMA on a particulate composite made of glass beads and a polystyrene matrix, at a larger scale. Both examples show how virtual DMA can contribute to question, analyze, and understand relaxation phenomena on either theoretical or experimental points of view.]]></description>
      <pubDate>Thu, 15 Apr 2021 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.6450</link>
      <guid>https://doi.org/10.46298/jtcam.6450</guid>
      <author>André, Stéphane</author>
      <author>Boisse, Julien</author>
      <author>Noûs, Camille</author>
      <dc:creator>André, Stéphane</dc:creator>
      <dc:creator>Boisse, Julien</dc:creator>
      <dc:creator>Noûs, Camille</dc:creator>
      <content:encoded><![CDATA[FFT-based solvers are increasingly used by many researcher groups interested in modelling the mechanical behavior associated to a heterogeneous microstructure. A development is reported here that concerns the viscoelastic behavior of composite structures generally studied experimentally through Dynamic Mechanical Analysis (DMA). A parallelized computation code developed with complex-valued quantities provides virtual DMA experiments directly in the frequency domain on a heterogeneous system described by a voxel grid of mechanical properties. The achieved precision and computation times are very good. An effort has been made to illustrate the application of such a virtual DMA tool through two examples from the literature: the modelling of glassy/amorphous systems at a small scale and the modelling of experimental data obtained in temperature sweeping mode by DMA on a particulate composite made of glass beads and a polystyrene matrix, at a larger scale. Both examples show how virtual DMA can contribute to question, analyze, and understand relaxation phenomena on either theoretical or experimental points of view.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>Brittle material strength and fracture toughness estimation from four-point bending test</title>
      <description><![CDATA[The failure stress under four-point bending cannot be considered as an intrinsic material property because of the well-known size effect of increasing maximum flexural stress with decreasing specimen size. In this work, four-point bending tests are analyzed with the coupled criterion for different sample sizes. The maximum flexural stress only tends towards the material tensile strength provided the specimen height is large enough as compared to the material characteristic length. In that case, failure is mainly driven by a stress criterion. Failure of smaller specimens is driven both by energy and stress conditions, thus depending on the material tensile strength and fracture toughness. Regardless of the material mechanical properties, we show that the variation of the ratio of maximum flexural stress to strength as a function of the ratio of specimen height to material characteristic length follows a master curve, for which we propose an analytical expression. Based on this relation, we propose a procedure for the post-processing of four-point bending tests that allows determining both the material tensile strength and fracture toughness. The procedure is illustrated based on four-point bending experiments on three gypsum at different porosity fractions.]]></description>
      <pubDate>Tue, 09 Mar 2021 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jtcam.6753</link>
      <guid>https://doi.org/10.46298/jtcam.6753</guid>
      <author>Doitrand, Aurélien</author>
      <author>Henry, Ronan</author>
      <author>Meille, Sylvain</author>
      <dc:creator>Doitrand, Aurélien</dc:creator>
      <dc:creator>Henry, Ronan</dc:creator>
      <dc:creator>Meille, Sylvain</dc:creator>
      <content:encoded><![CDATA[The failure stress under four-point bending cannot be considered as an intrinsic material property because of the well-known size effect of increasing maximum flexural stress with decreasing specimen size. In this work, four-point bending tests are analyzed with the coupled criterion for different sample sizes. The maximum flexural stress only tends towards the material tensile strength provided the specimen height is large enough as compared to the material characteristic length. In that case, failure is mainly driven by a stress criterion. Failure of smaller specimens is driven both by energy and stress conditions, thus depending on the material tensile strength and fracture toughness. Regardless of the material mechanical properties, we show that the variation of the ratio of maximum flexural stress to strength as a function of the ratio of specimen height to material characteristic length follows a master curve, for which we propose an analytical expression. Based on this relation, we propose a procedure for the post-processing of four-point bending tests that allows determining both the material tensile strength and fracture toughness. The procedure is illustrated based on four-point bending experiments on three gypsum at different porosity fractions.]]></content:encoded>
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