Publications

2020

• Cellular transduction of mechanical oscillations in plants by the plasma-membrane mechanosensitive channel MSL10
  
  • Tran Daniel
  • Guichard Marjorie
  • Thomine Sébastien
  • Leblanc-Fournier Nathalie
  • Moulia Bruno
  • de Langre Emmanuel
  • Allain Jean-Marc
  • Frachisse Jean-Marie
  Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences, 2020, 118 (1), pp.7 p.. Plants spend most of their life oscillating around 1–3 Hz due to the effect of the wind. Therefore, stems and foliage experience repetitive mechanical stresses through these passive movements. However, the mechanism of the cellular perception and transduction of such recurring mechanical signals remains an open question. Multimeric protein complexes forming mechanosensitive (MS) channels embedded in the membrane provide an efficient system to rapidly convert mechanical tension into an electrical signal. So far, studies have mostly focused on nonoscillatory stretching of these channels. Here, we show that the plasma-membrane MS channel MscS-LIKE 10 (MSL10) from the model plant Arabidopsis thaliana responds to pulsed membrane stretching with rapid activation and relaxation kinetics in the range of 1 s. Under sinusoidal membrane stretching MSL10 presents a greater activity than under static stimulation. We observed this amplification mostly in the range of 0.3–3 Hz. Above these frequencies the channel activity is very close to that under static conditions. With a localization in aerial organs naturally submitted to wind-driven oscillations, our results suggest that the MS channel MSL10, and by extension MS channels sharing similar properties, represents a molecular component allowing the perception of oscillatory mechanical stimulations by plants. (10.1073/pnas.1919402118)
  DOI : 10.1073/pnas.1919402118
• Personalized pulmonary mechanics : modeling, estimation and application to pulmonary fibrosis
  
  • Patte Cécile
  , 2020. Idiopathic pulmonary fibrosis (IPF), an interstitial lung disease, strongly impacts lung mechanics, which raises clinical issues. The objective of this work is to improve the understanding and diagnosis of IPF based on poromechanical modeling of the lung, personalized with clinical imaging data. In a first part, a literature review analyzes the state of the art of pulmonary physiology in relation to the existing mechanical models, insisting on the multi-scale, multi-phase and multi-physics characteristics of the organ. We then propose a poromechanical model of the lung at the organ spatial scale and breathing time scale, derived from a general poromechanical theory formulated recently in the MΞDISIM team. The constitutive law proposed reproduces mainly the pressure-volume behaviour of the lung as well as the quasi-incompressiblity of the solid phase. The boundary conditions take into account the lung environment (thoracic cage, diaphragm, pleura) and distinguish between free and ventilated breathing. The unloaded configuration, non observed during a breathing cycle, is estimated, with a special attention given to maintain a positive porosity. Various elements of the model are then personalized with standard clinical data, i.e., two 3DCT images acquired at end-exhalation and end-inhalation. In particular, an inverse problem is formulated to estimate the pulmonary compliance of the healthy and fibrotic regions, since the poromechanical formulation allows to distinguish the effect of the porosity from that of the absolute compliance of the interstitial tissue. Applied to three patients suffering from IPF, the personalized model allows to find the foreseen properties of IPF, i.e., the stiffening of the diseased region. Stress concentrations are also observed at the diseased region interface, supporting the hypothesis of a mechanical vicious circle governing the IPF progress, where fibrosis induces large stresses, which in turn favors fibrosis. This numerical tool could later be used for objective and quantitative diagnosis of IPF and, with longitudinal data, to study the mechanics-induced remodeling.
• Application of sound synthesis of piano tones to study the vibroacoustics of piano soundboards
  
  • Elie Benjamin
  • Cotté Benjamin
  • Boutillon Xavier
  , 2020, pp.2151-2153. We present the framework of MAESSTRO, which is a software for the Computer-Aided Design of piano soundboards. Based on sound synthesis of piano tones using physical models, it aims at assisting piano makers by providing them the opportunity to predict the mechanical behavior of virtual soundboards and the resulting sounds pf the piano in playing situation. The software is designed so that the synthesized tones reflect faithfully the mechanical and geometrical properties of the soundboard. It uses physical models that numerically simulate the phenomena that are involved in the production of piano sounds, from the impact of the hammer on the string to the radiated sound. We present applications that show the different functionalities of the software, including computing the modal basis of soundboards, studying the driving point admittance along the bridges, and the homogeneity of acoustic features along the tessitura. These applications are helpful to study the mechanical and acoustical impacts of structural modifications of a virtual soundboard. (10.48465/fa.2020.0781)
  DOI : 10.48465/fa.2020.0781
• Multipatch isogeometric mortar methods for thick shells
  
  • Adam Nicolas
  • Le Tallec Patrick
  • Zarroug Malek
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2020, 372, pp.113403. This paper introduces, analyzes and validates isogeometric mortar methods for the solution of thick shells problems which are set on a multipatch geometry. A particular attention will be devoted to the introduction of a proper formulation of the coupling conditions, with a particular interest on augmented lagrangian formulations, to the choice and validation of mortar spaces, and to the derivation of adequate integration rules. The relevance of the proposed approach is assessed numerically on various significative examples. (10.1016/j.cma.2020.113403)
  DOI : 10.1016/j.cma.2020.113403
• A flexible framework for sequential estimation of model parameters in computational hemodynamics
  
  • Arthurs Christopher J
  • Xiao Nan
  • Moireau Philippe
  • Schaeffter Tobias
  • Figueroa Alberto Alberto
  Advanced Modeling and Simulation in Engineering Sciences, Springer, 2020, 7. A major challenge in constructing three dimensional patient specific hemodynamic models is the calibration of model parameters to match patient data on flow, pressure, wall motion, etc. acquired in the clinic. Current workflows are manual and time-consuming. This work presents a flexible computational framework for model parameter estimation in cardiovascular flows that relies on the following fundamental contributions. (i) A Reduced-Order Unscented Kalman Filter (ROUKF) model for data assimilation for wall material and simple lumped parameter network (LPN) boundary condition model parameters. (ii) A constrained least squares augmentation (ROUKF-CLS) for more complex LPNs. (iii) A "Netlist" implementation, supporting easy filtering of parameters in such complex LPNs. The ROUKF algorithm is demonstrated using non-invasive patient-specific data on anatomy, flow and pressure from a healthy volunteer. The ROUKF-CLS algorithm is demonstrated using synthetic data on a coronary LPN. The methods described in this paper have been implemented as part of the CRIMSON hemodynamics software package. (10.1186/s40323-020-00186-x)
  DOI : 10.1186/s40323-020-00186-x
• Experimental identification of fracture toughness of a carbon black-filled styrene butadiene rubber undergoing energy dissipation by Mullins softening
  
  • Roucou David
  • Diani Julie
  • Brieu Mathias
  • Colombo Davide
  Mechanics of Materials, Elsevier, 2020, 151, pp.103645. (10.1016/j.mechmat.2020.103645)
  DOI : 10.1016/j.mechmat.2020.103645
• Efficacy of Almitrine in the Treatment of Hypoxemia in Sars-Cov-2 Acute Respiratory Distress Syndrome
  
  • Barthélémy Romain
  • Blot Pierre-Louis
  • Tiepolo Ambre
  • Le Gall Arthur
  • Mayeur Claire
  • Gaugain Samuel
  • Morisson Louis
  • Gayat Etienne
  • Mebazaa Alexandre
  • Chousterman Benjamin Glenn
  Chest, American College of Chest Physicians, 2020, 158, pp.2003 - 2006. No abstract available (10.1016/j.chest.2020.05.573)
  DOI : 10.1016/j.chest.2020.05.573
• Variational upscaling for modeling state of strain-dependent behavior and stress-induced crystallization in rubber-like materials
  
  • Diani Julie
  • Le Tallec Patrick
  Continuum Mechanics and Thermodynamics, Springer Verlag, 2020. The purpose of this paper is to present a general upscaling strategy for deriving macroscopic constitutive laws for rubber-like materials from the knowledge of the network distribution and a mechanical description of the individual chains and of their free energy. The microscopic configuration is described by the position of the cross-links and is not obtained by an affine assumption but by minimizing the corresponding free energy on stochastic large representative volume elements with adequate boundary conditions. This general framework is then approximated by using a microsphere (directional) description of the network. It is presented in a global setting and is extended in order to handle situations with tube-like constraints and stress-induced crystallization. (10.1007/s00161-020-00954-5)
  DOI : 10.1007/s00161-020-00954-5
• Analyse de la plasticité cyclique d'un acier TWIP et du rôle du maclage/démaclage à l'aide d'imagerie et de mesures de champs sub-micrométriques
  
  • d'Hondt Clément
  , 2020. L’objectif de la thèse est d’approfondir la compréhension de la plasticité cyclique des aciers TWIP et du rôle joué par le maclage / démaclage lors du durcissement cyclique en suivant l’activité de maclage à l’aide d’imagerie et de mesures de champs de déformation plastique submicrométriques, échelle permettant de discerner les nano-macles. La contrainte seuil de maclage en traction a été estimée entre 400 et 475 MPa. Le démaclage (pouvant être accompagné d’un maclage secondaire sur les systèmes coplanaires aux macles primaires), lors de l’inversion du chargement, et le remaclage, lors de la rampe de traction suivante, ont été mis en évidence en traction - compression lors d’essais in situ sous AFM et sous MEB avec corrélation d’images. Un niveau de contrainte en valeur absolue proche de la contrainte seuil de maclage semble nécessaire pour activer le démaclage et le remaclage. La contrainte en retour exercée par les grains voisins freine la croissance des macles primaires et favorise le démaclage et le maclage secondaire. A amplitude de contrainte imposée, la fraction maclée stagne après le premier cycle alors qu’à amplitude de déformation plastique imposée elle augmente lors du durcissement cyclique. Dans les deux cas, le maclage / démaclage accommode une fraction décroissante de l’amplitude de déformation plastique. A l’échelle macroscopique, le durcissement cyclique est suivi d’un adoucissement plus modeste. L’intensité de ces deux stades varie avec l’amplitude imposée. A amplitude de déformation plastique imposée, le durcissement est majoritairement du à l’augmentation de la composante cinématique (X) de la contrainte d’écoulement, qui a été associée au maclage, aux cellules de dislocations et aux fautes d’empilement, alors que l’adoucissement est majoritairement du à la diminution de la composante isotrope (R), qui a été attribuée à la destruction de l’ordre à courte distance. A amplitude de contrainte imposée, R suit une évolution similaire et X démarre à une valeur élevée, due au maclage intense lors de la première traction, et évolue ensuite assez peu. Une loi de comportement simulant convenablement les essais a été identifiée à partir des données recueillies à amplitude de déformation plastique imposée.
• Free vibrations of linear viscoelastic polymer cantilever beams
  
  • Diani Julie
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2020, 348 (10-11), pp.797-806. The free vibrations of cantilever slender beams of polymers, which are viscoelastic materials, are theoretically described using the simple Euler–Bernoulli assumption. The comparison between the theory and the experimental data collected for a thermoplastic elastomer, polyether block amide, shows very satisfactory results. Consequently, the theory is used for a thoughtful analysis of the impact of the material parameters and the beam geometry on its free vibration. Finally, the comparison of the dynamic behaviors of two polymers, using the free vibration test and a simple uniaxial tension/relaxation test, is discussed. (10.5802/crmeca.15)
  DOI : 10.5802/crmeca.15
• Computation of the exact discrete transparent boundary condition for 1D linear equations
  
  • Fliss Sonia
  • Imperiale Sébastien
  • Tonnoir Antoine
  , 2020. In this work, we are interested in the construction of the exact transparent boundary conditions for a semi-discretized and fully discretized 1D linear PDE. The proposed method is quite general and is based on the computation of a family of canonical functions. Several examples and numerical results to illustrate the method are presented.
• Corrosion‐fatigue behaviour of Cr–Mo steel under biaxial tension
  
  • Gaur Vidit
  • Doquet Véronique
  • Persent Emmanuel
  • Roguet Eléonore
  Fatigue and Fracture of Engineering Materials and Structures, Wiley-Blackwell, 2020, 43 (11), pp.2560-2570. Combined cyclic tension and internal pressure tests with various proportions of each loading were run on a 2.5%Cr–1%Mo steel in air and in 3.5% NaCl solution, with and without cathodic protection to investigate the effect of positive stress biaxiality on corrosion‐fatigue lives and damage mechanisms. At free potential, a strong reduction in fatigue resistance was observed for uniaxial as well as for equibiaxial cyclic tension and attributed to multiple crack initiation from corrosion pits. Cathodic protection completely cancelled the detrimental effect of the corrosive environment on fatigue lives whatever the load biaxiality was, in spite of an obvious enhancement of intergranular fracture attributed to hydrogen embrittlement. (10.1111/ffe.13276)
  DOI : 10.1111/ffe.13276
• A coupled electromagnetic-thermomechanical approach for the modeling of electric motors
  
  • Hanappier N
  • Charkaluk E
  • Triantafyllidis N
  , 2020. Future developments of lighter, more compact and powerful motors-driven by environmental and sustainability considerations in the transportation industry-involve higher stresses, currents and electromagnetic fields. Strong couplings between mechanical, thermal and electromagnetic effects will consequently arise and a consistent multiphysics modeling approach is required for the motors' design. Typical simulations-the bulk of which are presented in the electrical engineering literature-involve a stepwise process, where the resolution of Maxwell's equations provides the Lorentz and magnetic forces which are subsequently used as the external body forces for the resolution of Newton's equations of motion. The work presented here proposes a multiphysics setting for the boundary value problem of electric motors. Using the direct approach of continuum mechanics, a general framework that couples the electromagnetic , thermal and mechanical fields is derived using the basic principles of thermodynamics. Particular attention is paid to the derivation of the coupled constitutive equations for isotropic materials under small strain but arbitrary magnetization. As a first application, the theory is employed for the analytical mod-eling of an idealized asynchronous motor for which we calculate the electric current, magnetic, stress and temperature fields as a function of the applied current and slip parameter. The different components of the stress tensor and body force vector are compared to their purely mechanical counterparts due to inertia, quantifying the significant influence of electromagnetic phenomena.
• Tensile and ductile fracture properties of as-printed 316L stainless steel thin walls obtained by directed energy deposition
  
  • Margerit Pierre
  • Weisz-Patrault Daniel
  • Ravi-Chandar Krishnaswamy
  • Constantinescu Andrei
  Additive Manufacturing, Elsevier, 2020, 37, pp.101664. Mechanical properties of as-printed 316L stainless steel thin-walled structures obtained by directed energy deposition are investigated. In-situ tensile and fracture tests are performed on small samples obtained from a additively manufactured square section tube and extracted with three different orientations with respect to the part build direction. Despite a strongly oriented microstructure resulting from the process, as-printed specimens exhibit a reduced anisotropy in comparison with thick or polished samples commonly reported in the literature. Moreover, it is shown using a simple model that the reduced dentified anisotropy can be explained by considering the material thickness variation pattern only, resulting from the layer stacking process. Fracture tests are analyzed using an adapted digital image correlation procedure that evaluates the specimen fracture toughness from experimentally computed J-integrals. Using time reversal, strain fields in regions close to the crack path are identified. Stress fields are then computed from the constitutive behavior identified in tensile tests. A regularization procedure is proposed to enforce the stress equilibrium. Finally, the J-integral is computed using various integration contours in order to validate its path-independance. On this basis, a nearly isotropic fracture toughness is identified. Additional scanning electron microscope observations show that fracture surface features are independent from specimen orientation. This apparent isotropy is explained by the isotropic distribution of lack-of-fusion defects driving crack initiation and propagation. (10.1016/j.addma.2020.101664)
  DOI : 10.1016/j.addma.2020.101664
• Investigation of microstructure evolution and mechanical properties in cardiac tissue
  
  • Tueni N.
  • Vizet J.
  • Pierangelo A.
  • Allain J.-M.
  • Genet Martin
  Computer Methods in Biomechanics and Biomedical Engineering, Taylor & Francis, 2020, 23 (sup1), pp.S297-S299. (10.1080/10255842.2020.1816296)
  DOI : 10.1080/10255842.2020.1816296
• Theoretical and numerical modeling of magnetorheological elastomers comprising magnetically soft and hard particles
  
  • Mukherjee Dipayan
  , 2020. Particle-filled magnetorheological elastomers (MREs) are essentially two-phase composites comprising magneto-active metallic inclusions in a mechanically soft elastomer matrix. This work provides a set of equivalent microstructurally-guided constitutive models for isotropic MREs in the F-H, F-h, F-B and F-b variable spaces. Depending on the magnetic properties of the inclusion phases, the MREs are referred to as soft (s-MREs) or hard (h-MREs), if they contain, respectively, magneto-active (e.g., iron) or permanently magnetizable (e.g., NdFeB) particles. In turn, the non-coercive, ``soft'' magneto-active particles exhibit a saturation-type magnetization response, whereas highly coercive, permanently magnetizable ``hard'' magnetic particles exhibit ferromagnetic hysteresis.Two equivalent, h and b-based, thermodynamically consistent, rate-independent models for the ferromagnetic hysteresis are proposed herein. Furthermore, the non-hysteretic saturation-type soft magnetic response is observed to be a special case of the hysteresis response, in the limit of vanishing coercivity. A full-field numerical homogenization is subsequently carried out, in order to estimate the macroscopic response of the s- and h-MREs. In particular, an augmented, incremental numerical homogenization framework is proposed, that is suitable for the h-MREs. This incremental framework simplifies further in the limit of vanishing particle coercivity, thus leading to a purely energetic homogenization problem for the s-MREs. Numerical homogenization estimates for both s- and h-MREs provide crucial insights into the particle rearrangements and rotations under various loading conditions.Fully objective, explicit macroscopic models, that become exact to the analytical homogenization estimates in certain limits, are proposed for the s-MREs in both F-H and F-B variable spaces. Since most of the effective properties are estimated from the limiting cases of analytical homogenization, the number of model parameters to be estimated via model response fitting reduces to one. Similarly, fully objective, equivalent constitutive models in the F-H, F-h, F-b and F-b variable spaces are proposed for the h-MREs, where the internal variables in the Lagrangian F-H and F-B-based formulations are considered to be in a stretch-free, intermediate configuration. Consequently, the total Cauchy stress­­derived from the Clausius-Duhem inequalities via employing the classical Coleman-Noll-Gurtin methodis found to be consisting of the mechanical stress and the energetic and remanent Maxwell stresses, where the last is an additional stress contribution obtained for the h-MREs. Furthermore, the evolution equation for the current internal variables are defined to be in terms of their objective Green-Naghdi rates. Here also, only one additional model parameter, to be identified via fitting the model response, is introduced.Excellent agreements are obtained between the proposed models for the s- and h-MREs and the numerical homogenization estimates for all particle volume fractions of interest, i.e., up to 30%, and for moderately-soft to relatively stiff matrix phases having shear moduli G_m > 0.3 MPa. In turn, the proposed s-MRE models also perform extremely well for softer matrices having moduli G_m < 0.1 MPa.
• Probabilistic Low Cycle Fatigue criterion for nodular cast-irons
  
  • Szmytka Fabien
  • Charkaluk Eric
  • Constantinescu Andrei
  • Osmond Pierre
  International Journal of Fatigue, Elsevier, 2020, 139, pp.105701. This paper proposes an original method for characterising the Low Cycle Fatigue (LCF) lifetime using probability density functions. The protocol is based on statistics of microstructure heterogeneities taken as damage initiation sites, a qualitative mechanical analysis of the heterogeneities harmfulness and the definition of a micro-crack growth law. The technique is here established and the associated model identified for a nodular cast iron where the graphite nodules are assumed to be the damage initiation zones. The LCF lifetime is characterised from both a large set of experimental test between 300 and 600 • C and damage observations at the micro-scale. Experimental post-mortem observation combined with a simple numerical study first enable to assume the harmfulness of nodules according to their size and their probable role in the damage process A probability density function for the lifetime is then built from the following steps: (i) a quantitative analysis of the material micro-structure, which provides the probability density of nodules occurrence depending of their size (ii) an extreme value analysis using a Gumbel distribution and (iii) a micro-crack growth law associated with LCF conventional terms of energy densities. Its parameters are obtained using an optimisation process applied to laboratory fatigue experiment. The obtained probability function provides a good match for the lifetime and greatly improves results given by conventional criteria. It moreover provides a robust estimate of the lifetime scatter for different types of fatigue tests. (10.1016/j.ijfatigue.2020.105701)
  DOI : 10.1016/j.ijfatigue.2020.105701
• Asymptotic modelling of Skin-effects in coaxial cables
  
  • Beck Geoffrey
  • Imperiale Sébastien
  • Joly Patrick
  SN Partial Differential Equations and Applications, Springer, 2020, 1. In this work we tackle the modeling of non-perfectly conducting thin coaxial cables. From the non-dimensionnalised 3D Maxwells equations, we derive, by asymptotic analysis with respect to the (small) transverse dimension of the cable, a simplified effective 1D model and an effective reconstruction procedure of the electric and magnetic fields. The derived effective model involves a fractional time derivatives that accounts for the so-called skin effects in highly conducting regions. (10.1007/s42985-020-00043-x)
  DOI : 10.1007/s42985-020-00043-x
• Determining upper and lower bounds for steady state strain rate during a creep test on a salt sample
  
  • Gharbi Hakim
  • Berest Pierre
  • Blanco Martín Laura
  • Brouard Benoît
  International Journal of Rock Mechanics and Mining Sciences, Pergamon and Elsevier, 2020, 134, pp.104452. A creep test performed on a Landes salt sample during one year and a half is described. During the first year, a 0.6 MPa axial load is applied to the sample. At the end of this one-year phase, strain rate (9×10−12s-1) is much faster than the strain rate extrapolated from high-stress tests. Steady state strain rate is not reached. In an attempt to reach steady state strain rate “from below”, a 0.9 MPa load is applied during two days before restoring the initial load (0.6 MPa). After the load is restored, reverse creep is observed first (strain rate sign changes before vanishing to zero after a few hours). Then, strain rate increases to reach 5×10−12s-1 after five months, slower than the strain rate before the load change. Commonly accepted constitutive laws can explain this effect, which provides a lower and an upper bound for steady state strain rate. This note presents a method to determine such bounds. (10.1016/j.ijrmms.2020.104452)
  DOI : 10.1016/j.ijrmms.2020.104452
• Méthodes isogéométrique multipatch pour des coques épaisses non linéaires avec contact
  
  • Adam Nicolas
  , 2020. Le concept d'analyse isogéométrique généralise la méthode des éléments finis par l'utilisation de fonctions splines plus riches que les traditionnelles fonctions de Lagrange qui imposent l'approximation de la géométrie considérée. Sa principale motivation est de lier plus fortement la conception à l'analyse par l'utilisation des mêmes modèles géométriques comme supports pour la création et la simulation numérique. La méthode isogéométrique a connu ces dernières années une activité de recherche très soutenue et elle intéresse aussi bien le monde académique que le monde industriel. De par la construction des fonctions splines, la géométrie issue d'un logiciel de conception est nécessairement composée de plusieurs domaines (ou patchs). La majeure partie des applications visées par les travaux publiés à ce jour concerne des pièces simples, constituées de quelques patchs voir même d'un seul, et ne sont donc pas applicables au contexte industriel. Certains champs d'applications restent encore à développer tel que le couplage multipatch ainsi que le contact afin de traiter de manière robuste et efficace des géométries complexes en petites et grandes transformations. Cette thèse s'inscrit dans un contexte industriel lié à l'automobile pour lequel la majorité des pièces sont des structures minces modélisables par des coques épaisses. L'un des principaux enjeux est de mettre en place la méthode isogéométrique multipatch, permettant l'utilisation de grandeurs cinématiques exactes, pour des coques de type Reissner-Mindlin nécessitant un traitement efficace du verrouillage numérique. Une méthode originale permettant de traiter le cas des grands déplacements, avec en particulier des grandes rotations de normale, est proposée. Le développement de méthodes de couplage multipatch et de contact non frottant associées à un modèle de coque épaisse non linéaire permet d'insérer la méthode isogéométrique dans un contexte industriel exigeant.
• Combined Estimation of Material Law and Unloaded Configuration (Application to Pulmonary Poro-Mechanics)
  
  • Manoochehrtayebi Mahdi
  , 2020.
• On the thermo-mechanical theory of field dislocations in transient heterogeneous temperature fields
  
  • Upadhyay Manas Vijay
  , 2020. A strong coupling between the field theory of dislocation mechanics and heat conduction is proposed. The novel model, called the thermal field dislocation mechanics (T-FDM) model, is designed to study the dynamics of dislocations during rapid or gradual temperature changes in a body having a heterogeneous temperature distribution; for example, such conditions occur in a heat-affected crystalline solid during an additive manufacturing process. Thermal strains are uniquely separated into compatible and incompatible components via the Stokes-Helmholtz decomposition and the curl of the incompatible part of thermal strains is directly related to the areal dislocation density tensor. A dislocation density evolution (including transport) law is developed and shown to be related to the evolution of the curl of incompatible thermal strains. This relationship demonstrates that dislocation generation, annihilation, motion and/or interactions with other defects can be triggered due to transient temperature changes, and conversely an evolving dislocation density induces temperature changes. The model development is completed with constitutive laws derived from energetic and dissipative considerations. The advantages and consequences of the assumptions of the T-FDM model under rapidly changing temperatures, both spatially and temporally, are discussed. The T-FDM model is intended for application at the length scale where individual dislocations can be characterized. At this level, local thermodynamic equilibrium is found to be a reasonable assumption even for high rates of change of temperature such as those occurring during an additive manufacturing process. Some illustrative examples are presented to demonstrate the applicability of the model and to better understand some of the novel concepts proposed in this work.
• Fluage à long terme de l’argilite de Bure sous faible charge uniaxiale et en extension/compression triaxiale et compression uniaxiale avec suivi in-situ
  
  • Dimanov Alexandre
  • Bornert Michel
  • Gharbi Hakim
  • Talandier Jean
  , 2020.
• Deformation Patterns and their Stability in Finitely Strained Circular Cell Honeycombs
  
  • Combescure Christelle
  • Elliott Ryan
  • Triantafyllidis Nicolas
  Journal of the Mechanics and Physics of Solids, Elsevier, 2020, 142, pp.103976. The mechanics of cellular honeycombs-part of the rapidly growing field of architected materials-in addition to its importance for engineering applications has a great theoretical interest due to the complex bifurcation mechanisms leading to failure in these nonlinear structures of high initial symmetry. Of particular interest to this work are the deformation patterns and their stability of finitely strained circular cell honeycomb. Given the high degree of symmetry of these structures, the introduction of numerical imperfections is inadequate for the study of their behavior past the onset of first bifurcation. Thus, we further develop and explain a group-theoretic approach to investigate their deformation patterns, a consistent and general methodology that systematically finds bifurcated equilibrium orbits and their stability. We consider two different geometric arrangements, hexagonal and square, biaxial compression along loading paths, either aligned or at an angle with respect to the axes of orthotropy, and different constitutive laws for the cell walls which can undergo arbitrarily large rotations, as required by the finite macroscopic strains applied. We find that the first bifurcation in biaxially loaded hexagonal honeycombs of infinite extent always corresponds to a local mode, which is then followed to find the deformation pattern and its stability. Depending on load path orientation, these first bifurcations can be simple, double or even triple. All bifurcated orbits found are unstable and have a maximum load close to their point of emergence. In contrast, the corresponding instability in square honeycombs always corresponds to a global mode and hence the deformation pattern will depend on specimen size and boundary conditions. (10.1016/j.jmps.2020.103976)
  DOI : 10.1016/j.jmps.2020.103976
• Ultrasounds could be considered as a future tool for probing growing bone properties
  
  • Lefevre Emmanuelle
  • Baron Cécile
  • Gineyts Evelyne
  • Bala Yohann
  • Gharbi Hakim
  • Allain Jean-Marc
  • Lasaygues Philippe
  • Pithioux Martine
  • Follet Hélène
  Scientific Reports, Nature Publishing Group, 2020, 10, pp.15698. (10.1038/s41598-020-72776-z)
  DOI : 10.1038/s41598-020-72776-z