Publications

2012

• Mechanical modeling of crawling cells
  
  • Recho Pierre
  , 2012. The ability of most eukaryotic cells to crawl is essential for embryogenesis, immune response and wound healing while functional abnormalities of crawling can provoke different diseases including cancer. Artificial biomimetic machines mimicking eukaryotic cells are of interests as prototypes of versatile engineering devices operating autonomously at a nano-scale. A prototypical scheme of cell motility includes polymerization of actin network coupled with dynamic assembly of focal adhesions, myosin-driven contraction and, finally, the detachment of adhesive contacts followed by de-polymerization which closes the treadmilling cycle. The motor part of an eukaryotic cell is a layer of an active gel whose functions are controlled by complex chemical and mechanical processes. In particular, the coordinated movements of this gel resulting in crawling involve spatial and temporal self-organization at the cytoskeletal level and require a continuous supply of energy. While the molecular and biochemical basis of cell motility is basically known, the qualitative understanding of the mechanical interplay between different active components is still limited despite many recent attempts to construct comprehensive mathematical models. This manuscript aims at presenting an analysis of a simple and one dimensional model accounting for cell crawling. The first chapter is dedicated to optimization of speed and mechanical efficiency of crawling. Our analysis shows that the obtained optimal distribution of contractile stresses and the optimal friction distribution are in good agreement with the observed distributions. In the second chapter, we propose a mechanism of cell motility which places emphasis on contraction while ignoring actin treadmilling. At the basis of the model is contraction driven uphill diffusion destabilizing symmetric configuration and causing polarization. The morphological instability is due to spontaneous internal motion of the cytoskeleton which is generated by active cross-linkers and simultaneously transports them. By studying the simplest one dimensional problem we show that such internal flow can generate steady propulsion of a finite cell body. The model exhibits motility initiation patterns similar to the ones observed in experiments. In the last chapter we focus on actin treadmilling-based motility which allows the cell not only to self-propel but also exert forces on obstacles (to push) and carry cargoes (to pull). We use a minimal one dimensional model of the crawling cell to show that the pushing dominated force-velocity relation is controlled by the protrusion mechanism. Instead, the pulling dominated force-velocity relation is controlled by the protrusion mechanism only at small values of the force which is replaced by the contraction mechanism at sufficiently large forces.
• Micromechanical experimental investigation and modelling of strain and damage of argillaceous rocks under combined hydric and mechanical loads
  
  • Wang Linlin
  , 2012. The hydromechanical behavior of argillaceous rocks, which are possible host rocks for underground radioactive nuclear waste storage, is investigated by means of micromechanical experimental investigations and modellings. Strain fields at the micrometric scale of the composite structure of this rock, are measured by the combination of environmental scanning electron microscopy, in situ testing and digital image correlation technique. The evolution of argillaceous rocks under pure hydric loading is first investigated. The strain field is strongly heterogeneous and manifests anisotropy. The observed nonlinear deformation at high relative humidity (RH) is related not only to damage, but also to the nonlinear swelling of the clay mineral itself, controlled by different local mechanisms depending on RH. Irreversible deformations are observed during hydric cycles, as well as a network of microcracks located in the bulk of the clay matrix and/or at the inclusion-matrix interface. Second, the local deformation field of the material under combined hydric and mechanical loadings is quantified. Three types of deformation bands are evidenced under mechanical loading, either normal to stress direction (compaction), parallel (microcracking) or inclined (shear). Moreover, they are strongly controlled by the water content of the material: shear bands are in particular prone to appear at high RH states. In view of understanding the mechanical interactions a local scale, the material is modeled as a composite made of non-swelling elastic inclusions embedded in an elastic swelling clay matrix. The internal stress field induced by swelling strain incompatibilities between inclusions and matrix, as well as the overall deformation, is numerically computed at equilibrium but also during the transient stage associated with a moisture gradient. An analytical micromechanical model based on Eshelby's solution is proposed. In addition, 2D finite element computations are performed. Results are discussed in relation with experimental observations.
• Stress Corrosion Cracking of Nickel Base Alloys in PWR Primary Water
  
  • Guerre Catherine
  • Chaumun Elizabeth
  • Crépin Jérôme
  • De Curières Ian
  • Duhamel Cécilie
  • Héripré Eva
  • Herms Emmanuel
  • Laghoutaris Pierre
  • Molins Régine
  • Sennour Mohamed
  • Vaillant François
  , 2013, 51, pp.04003. (10.1051/epjconf/20135104003)
  DOI : 10.1051/epjconf/20135104003
• Étude multi-échelle des mécanismes de déformation ductile de polycristaux synthétiques de chlorure de sodium.
  
  • Bourcier Mathieu
  , 2012. Il existe un renouveau d'intérêt pour la rhéologie du sel gemme car les cavités salines sont des sites intéressants pour l'enfouissement de déchet ou le stockage d'énergie. Ces nouvelles recherches bénéficient du développement des techniques d'observation à petite échelle qui permettent une caractérisation précise des microstructures, des mécanismes de déformation et des champs de déformation. Une procédure pour fabriquer des échantillons de sel synthétiques ayant différentes tailles de grains, a été mise au point. Des essais macroscopiques ont été réalisés pour comparer le comportement du matériau synthétique et naturel. Des tests de compressions uniaxiale ont été réalisés sur des presses classiques et avec une machine spécifique installée dans un microscope électronique à balayage. Les images numériques de la surface de l'échantillon ont été enregistrées à différentes étapes de chargement. Des marqueurs ont permis de mesurer les déplacements grâce à la corrélation d'images numériques. Les champs de déformation globaux et locaux ont ainsi été calculés. L'analyse de ces résultats donne une mesure de l'hétérogénéité à différentes échelles, une estimation de la taille de l'élément de volume représentatif et enfin une identification des mécanismes de déformation, c'est à dire, la plasticité intracristalline et le glissement aux interfaces que l'on constate être en interactions locales complexes. Les chargements macroscopiques donnent lieu à des champs de contraintes locaux complexes du fait de l'orientation cristalline, la densité et l'orientation des interfaces et l'histoire locale de la déformation. Nous avons donné une estimation quantitative de l'importance relative de ces deux mécanismes pour plusieurs microstructures et mis en évidence un un effet marqué de la taille de grains. Nous avons aussi réalisé des simulations par éléments finis basées sur la plasticité cristalline et trouvé un bon accord avec les résultats expérimentaux pour l'identification des systèmes de glissement. Enfin, des développements expérimentaux 3D utilisant la tomographie aux rayons X sont montrés avec des résultats préliminaires.
• The inverse problem of seismic fault determination using part time measurements
  
  • Bui Huy Duong
  • Constantinescu Andrei
  • Maigre Hubert
  Journal of Mechanics of Materials and Structures, Mathematical Sciences Publishers, 2012, 7 (10). This paper shows how a part time measurement T of the acceleration on the ground can be done to avoid the consideration of reflections of seismic waves on the Moho discontinuity. A bounded hemispherical solid is considered with radius greater than cpT , but smaller than the Moho depth, in order to get the null boundary conditions on the hemispherical surface. The inverse problem to determine the fault plane and the time-dependent fault geometry is well-defined and solved in closed form by the reciprocity gap functional method. Two formulae are established for the components of the fault slip, which involve time and spatial Fourier transforms of some quantities related to the reciprocity gap functional. A forward initial boundary value problem in elastodynamics enables us to get the internal wave field, the shear stress as well as the normal stress on the fault. This full solution would be useful for understanding the friction mechanism on the fault during a real strike, whenever the initial uniform tectonic stresses are known from geophysical considerations. (10.2140/jomms.2012.7.997)
  DOI : 10.2140/jomms.2012.7.997
• Response to the comments by Hucthinson and Tvergaard
  
  • Danas Kostas
  • Ponte Castaneda Pedro
  International Journal of Solids and Structures, Elsevier, 2012, pp.3486.
• Optimization of Anticlastic Core Structures for Lightweight Sandwich Panels
  
  • Ebnöther Fabien
  , 2012. This thesis investigates the mechanical behavior of all-metal sandwich panels with anticlastic core structures. Anticlastic core structures provide a cost-effective alternative to hexagonal honeycomb core structures as these can be produced in a mass production environment through progressive stamping and embossing. Fracture during manufacturing limits the space of possible microstructural configurations of anticlastic core structures. The optimization of the load carrying capacity of sandwich panels with anticlastic core structures is therefore conducted under the constraint of ductile fracture. The choice of a suitable ductile fracture model for predicting the fracture of the basis sheet materials plays a central role in this research. The first part of this thesis is entirely devoted to the experimental and numerical evaluation of the predictive capabilities of the original stress-based and the mixed stress-strain based damage indicator version of the Mohr-Coulomb failure model. Limiting our attention to tension-dominated stress states between uniaxial and equi-biaxial tension of thin low carbon steel, basic fracture tests such as notched tension and circular punch test are carried out to identify the fracture model parameters. A Hasek test and the recordings during the stamping of an anticlastic structure are used to assess the predictive capabilities of both fracture models. It is found that the damage indicator model with stress state dependent weighting function predicts the onset of fracture in the stamping test with greater accuracy. In the second part of this thesis, the Mohr-Coulomb damage indicator model is used to determine the maximum stamping depth during the making of anticlastic core layers as a function of the tool geometry. The large deformation behavior is described through a quadratic plasticity model with an isotropic hardening law and a non-associated flow rule. Design maps are developed that express the effective core shear stiffness, the core shear strength, the delamination strength and elastic face sheet buckling as a function of the core layer geometry. A method to optimize the performance of anticlastic sandwich panels is presented for simply supported rectangular panels subject to uniform lateral loading. The results from the four-point bending experiments demonstrate that the optimized anticlastic sandwich panels provide a higher strength and stiffness (at a lower weight) than foamed HDPE panels. The last part of this thesis investigates the puncture resistance of all-metal sandwich panels with a stamped anticlastic core structure. The effect of the parameters describing the core geometry and the choice of the substrate materials is studied. In particular, a low carbon steel, a DP780 dual phase steel and an ultra-high strength martensitic steel as candidate materials for the face sheets. A newly-developed damage indicator model with a weighting function based on Hosford's criterion is employed to model the fracture response of these materials. A parametric finite element study is performed on the puncture resistance of sandwich panels covering different cell sizes for the anticlastic core structure. The analysis of the simulation results reveals that the puncture resistance decreases with the cell size and core height respectively, i.e. the thinner the sandwich panel the higher the puncture resistance. Selected experiments are also presented to support this important finding.
• Fracture of a borosilicate glass under triaxial tension
  
  • Doquet Véronique
  • Ben Ali Neji
  • Constantinescu Andrei
  • Boutillon Xavier
  Mechanics of Materials, Elsevier, 2012, 57, pp.15-29. The growth of 3D star-like cracks in a porous borosilicate glass was induced by "cold-to-hot" thermal shocks inducing triaxial tension in cylindrical specimens. As a consequence of the dynamic character of their propagation, the cracks had a "mirror- mist- hackle" aspect. Damage in unbroken specimens was characterized either by a modification of their vibration modes or by direct observations of sections. Pores were identified as the crack initiation sites. Thermo-mechanical simulations were done to analyze the stress field and its consequences, using either linear thermo-elasticity or an anisotropic continuum damage mechanics approach. Crack initiation was predicted at mid-height, at the center of the specimens, in accordance with the observations. The pore-induced stress concentration was shown to depend on the local stress triaxiality, as well as the stress intensity factor for an annular crack initiated from a pore. The capacity of the anisotropic continuum damage approach to predict qualitatively the influence of the shape of the specimen, as well as damage-induced modifications of vibration modes and the total fracture surface was demonstrated. (10.1016/j.mechmat.2012.10.008)
  DOI : 10.1016/j.mechmat.2012.10.008
• Energy Issues
  
  • Salençon Jean
  , 2012.
• Sounds good? Determination of a gas/brine interface by an acoustic method at Manosque
  
  • Brouard Benoit
  • Berest Pierre
  • Vincent De Greef
  • Gérard Gary
  • Crabeil Jean-Paul
  , 2012, pp.97-118. Water hammers commonly are observed at wellheads and often are considered a potential hazard that should be avoided. Nevertheless, there are a few situations in which water hammers provide very valuable information about a well. A comprehensive data-acquisition and analysis system has been developed by Brouard Consulting and Ecole Polytechnique. One potential application of that system is determining the depth of an interface between two fluids. This application has been tested successfully at the Manosque field. It is demonstrated here how this low-cost and non-intrusive system can be accurate and allows practical, real-time measurements.
• Tensile effective stresses in hydrocarbon storage caverns
  
  • Djizanne Hippolyte
  • Berest Pierre
  • Brouard Benoît
  , 2012, pp.223-240. The "no-tensile effective stress" criterion is discussed. It is proven that effective tensile stresses can be generated at a cavern wall after a rapid increase or decrease in pressure. The Etzel K-102 test, performed in Germany more than 20 years ago, is revisited using the notion of effective tensile stresses.
• Modeling and Simulation of the Cooling Process of Borosilicate Glass
  
  • Barth Nicolas
  • George Daniel
  • Ahzi Saïd
  • Rémond Yves
  • Doquet Véronique
  • Bouyer Frédéric
  • Bétremieux Sophie
  Journal of Engineering Materials and Technology, American Society of Mechanical Engineers, 2012, 134 (4), pp.041001. For a better understanding of the thermomechanical behavior of glasses used for nuclear waste vitrification, the cooling process of a bulk borosilicate glass is modeled using the finite element code Abaqus. During this process, the thermal gradients may have an impact on the solidification process. To evaluate this impact, the simulation was based on thermal experimental data from an inactive nuclear waste package. The thermal calculations were made within a parametric window using different boundary conditions to evaluate the variations of temperature distributions for each case. The temperature differences throughout the thickness of solidified glass were found to be significantly non-uniform throughout the package. The temperature evolution in the bulk glass was highly responsive to the external cooling rates applied; thus emphasizing the role of the thermal inertia for this bulky glass cast. (10.1115/1.4006132)
  DOI : 10.1115/1.4006132
• The power stroke driven muscle contraction
  
  • Sheshka Raman
  , 2012. This thesis is devoted to the modeling of mechanical functioning of myosin II/actin in- teraction, responsible for active force generation in skeletal muscles at nanometer scale. The muscle contractile units contain actin filament and myosin II filaments formed by an assembly of myosins II. The myosin II is molecular motor that periodically attaches and detaches to the actin filament in presence of ATP. In order to understand the phenomenon of muscle contraction from mechanical point of view, we follow the approach developed by the Brownian ratchets community, which replaced the conventional chemistry-based interpretation of active force generation by a study of Langevin dynamics of mechanical systems with well defined energy landscapes. We focus on the role of the conformational change known as power stroke in the functioning of myosin II. We identify the power stroke as the main driver of contractility. The attribution of active role to power stroke reflects the biological reality imprinted in the molecular motor functional cycle. We propose an innovative mechanical model and by emphasizing the active role of the power stroke we are therefore building a bridge between processive and nonprocessive motors. In this Thesis we present the first examples of models of nonprocessive motors driven exclusively by the power stroke and exploiting the well known phenomenon of stochastic resonance.
• three-dimensional analysis of fatigue crack paths in thin metallic sheets
  
  • Esnault Jean-Baptiste
  • Doquet Véronique
  • Massin Patrick
  , 2012. Fatigue crack growth in thin sheets of 7075 T651 aluminium alloy and S355 steel were characterized in 3D, using crack front markings and topographic reconstructions of fracture surfaces. Tests in air or in salt water produced different crack paths for similar mechanical conditions, shear lips being reduced by the corrosive environment, in the aluminium alloy as well as in steel. Before the onset of shear lips development, tunnelling crack fronts were observed, but tunnelling was progressively reduced and cancelled as slanted crack growth developed, even though KI is reduced by crack twisting. This indicates a significant contribution of shear modes to the crack driving force, even though mode I striations are still present on slanted zones. KI, KII and KIII were computed by X-FEM taking into account the real crack path. The crack growth rates correlated much better to than to KI. Elastic-plastic finite element simulations and the local application of a fatigue criterion with an amplitude-dependent critical plane qualitatively captured the transition in fracture mode in 7075 T651.
• Matching asymptotic method in propagation of cracks with Dugdale model
  
  • Dang Thi Bach Tuyet
  • Marigo Jean-Jacques
  • Halpern Laurence
  , 2012, 525-526, pp.489-492. The goal of this work is to apply the matching asymptotic method combined with a vari- ational approach to study the initiation and the propagation of a cohesive crack from the tip of a preexisting notch following the Dugdale cohesive force model when the characteristic length of the material (included in the Dugdale model) is small by comparison with the characteristic length of the body. (10.4028/www.scientific.net/KEM.525-526.489)
  DOI : 10.4028/www.scientific.net/KEM.525-526.489
• The effect of a thin layer of heterogeneities in an elastic structure
  
  • Geymonat Giuseppe
  , 2012.
• Modélisation de la fissuration des structures en béton soumises à des sollicitations sévères
  
  • Nguyen Truong-Giang
  , 2012. Le béton est un des matériaux de construction les plus répandus dans le monde. Cependant, dans de nombreux secteurs industriels, il est de plus en plus courant d'étudier les marges de sécurité d'un ouvrage vis à vis de sollicitations. Il devient important de prédire le mode de ruine de l'ouvrage. De nombreux travaux ont déjà été réalisés dans le monde sur ce sujet, conduisant à des modèles opérationnels dans des codes de calcul par éléments finis. Néanmoins, des difficultés subsistent, liées principalement à la fissuration du béton. Ces difficultés se traduisent par des problèmes ouverts concernant la localisation, l'initiation et la propagation des fissures. Le travail de thèse explore deux possibilités d'amélioration des méthodes de simulation numérique de propagation des fissures. La première possibilité d'amélioration concerne l'utilisation de la méthode des éléments finis étendus, XFEM (eXtended Finite Element Method). Une modélisation du comportement mécanique de fissure est introduite et conduit à une description de la propagation de fissure d'un élément à un autre. La deuxième possibilité est basée sur la mécanique de l'endommagement. Dans le cadre de la modélisation de l'endommagement de type standard généralisé, le phénomène de localisation a été étudié numériquement pour des comportements divers : endommagement visqueux ou fragile. Ces comportements sont décrits dans le même esprit que les lois de la visco-élasticité ou de la visco-plasticité ou de la plasticité classiques, à partir d'une interprétation thermodynamique générale. En particulier, les lois à gradient de l'endommagement sont aussi considérées en liaison avec des résultats récents de la littérature. Il est bien connu qu'un modèle à gradient permet d'interpréter les effets d'échelle des structures sous chargement mécanique. Il joue aussi un rôle intéressant dans les effets de localisation de la déformation.
• Influence of hydrogen and oxygen content on the mechanical behavior of zirconium between 275 and 325°C and titanium at 20°C
  
  • Couzinie Jean-Philippe
  • Barkia Bassem
  • Doquet Véronique
  • Guillot Ivan
  , 2014, pp.411-419. The mechanical behaviors of α-Zr and α-Ti with various oxygen and hydrogen contents were investigated by loading/relaxation/unloading tensile tests and tests with strain rate jumps, at 300°C and 20°C, respectively. Solute oxygen and hydrogen atoms were found to have antagonist effects. While the former increases the yield stress and hardening exponent, reduces the activation volume and enhances static and dynamic strain aging phenomena, the latter significantly reduces these effects, as long as the O content is not too high.
• thermodynamical model for strain-induced crystallization of rubber
  
  • Lê Thien-Nga
  • Guilie Joachim
  • Le Tallec Patrick
  , 2012.
• Pre-yield shearing regimes of magnetorheological fluids
  
  • Nassar Waad
  • Boutillon Xavier
  • Lozada José
  , 2012, pp.1-6. We analyzed experimentally the pre-yield regime of some MRFs. The hearing response is ruled by two successive regimes and limited by an interfacial phenomenon. The initial response is pseudo-elastic and independent from the magnetic field and of the particle volume fraction. The shear-stress limit of this regime is proportional to the square of the magnetic field and to the particle volume fraction. In the next regime, the shear strain is not uniform in the fluid. The increase in average shear stress varies linearly with the increase in average shear strain. The variation coefficient is proportional to the square of the magnetic field and decreases with the particle volume fraction. Finally, a loss of adhesion of the magnetic aggregates with the shearing plate or the magnetic pole occurs. The corresponding shear stress is proportional to the square of the magnetic field and to the particle volume fraction. (10.1115/SMASIS2012-8047)
  DOI : 10.1115/SMASIS2012-8047
• On the coupling between shape variation and material dissipation for computation of the crack driving force
  
  • Guilie Joachim
  • Le Tallec Patrick
  , 2012.
• A cyclic steady-state method for fatigue crack propagation: Evaluation of plasticity-induced crack closure in 3D
  
  • Lê Minh Bao
  • Doquet Véronique
  • Maitournam H.M.
  International Journal of Solids and Structures, Elsevier, 2012, 49 (17), pp.2301-2313. The numerical study of plasticity-induced crack closure using the node-release technique presents many difficulties widely studied in literature. For instance various rules, proposed for overcoming mesh sensi- tivity, are challenged by more recent studies. This paper intends to propose and evaluate a numerical method for the investigation of crack propagation under fatigue loading, and particularly for the assess- ment of plasticity-induced crack closure in three-dimension. The method is an extension of the ''steady- state method'' to cyclic loadings. The steady-state method allows a direct computation (on a fixed mesh, without releasing nodes) of stress and strain fields around the crack tip and in the wake for a steady crack growth. The method is extended to simulate crack propagation under fatigue loading. Therefore it con- stitutes a valuable numerical tool for gaining insight into the physics of crack propagation, as it provides accurate mechanical fields around the crack tip and their relation with crack growth rate, various loading modes and parameters. The proposed method is also compared with the classical node-release technique. A very good agreement between the two methods is found. However the steady-state method needs much less mesh refinement and computational time. Following an analysis of some features of the fatigue crack, a discussion on a crack closure criterion is opened, and a reliable criterion for the determination of local crack closure is proposed. (10.1016/j.ijsolstr.2012.04.040)
  DOI : 10.1016/j.ijsolstr.2012.04.040
• TMF criteria for Lost Foam Casting aluminum alloys
  
  • Tabibian Shadan
  • Charkaluk Eric
  • Constantinescu Andrei
  • Szmytka Fabien
  • Oudin Alexis
  Fatigue and Fracture of Engineering Materials and Structures, Wiley-Blackwell, 2012. The purpose of this paper is to define a thermo-mechanical fatigue criterion in order to predict the failure of aluminum alloys components issued with the lost foam casting process and used in particular in the automotive industry. The microstructure of the studied materials (A356-A319 aluminum alloys) is clearly affected by the lost foam casting process which can directly affect the mechanical properties, the damage mechanisms and the fatigue failure of specimens and components. The major problem in defining a predictive fatigue criterion in this case is the fact that it should be applicable for the component which is submitted to complex multiaxial thermo-mechanical loadings. Since many years, energy-based criteria have been used to predict fatigue failure of this class of materials. Then, different energy-based criteria are tested in order to take into account different types of triaxiality and mean stress effects corrections. The fatigue lifetime results predicted by both of them show a good agreement with experimental results. (10.1111/ffe.12006q)
  DOI : 10.1111/ffe.12006q
• A second gradient Reissner-Mindlin plate model via the asymptotic expansions method",
  
  • Serpilli Michèle
  • Geymonat Giuseppe
  • Krasucki Francoise
  , 2012, pp.p. 262-263.
• Une méthode de résolution efficace pour un problème multi-échelle en élasticité
  
  • Vidrascu Marina
  • Geymonat Giuseppe
  • Hendili Sofiane
  • Krasucki Françoise
  , 2012. Cette présentation décrit une méthode multi-échelle robuste et efficace qui combine développements asymptotiques raccordés et décomposition de domaines pour résoudre des problèmes d'élasticité avec un grand nombre d'hétérogénéités.