Publications

2015

• Modeling of smart materials with thermal effects: dynamic and quasi-static evolution
  
  • Bonaldi Francesco
  • Geymonat Giuseppe
  • Krasucki Françoise
  Mathematical Models and Methods in Applied Sciences, World Scientific Publishing, 2015, 25 (14), pp.2633-2667. We present a mathematical model for linear magneto-electro-thermo-elastic continua, as sensors and actuators can be thought of, and prove the well-posedness of the dynamic and quasi-static problems. The two proofs are accomplished, respectively, by means of the Hille-Yosida theory and of the Faedo-Galerkin method. A validation of the quasi-static hypothesis is provided by a nondimensionalization of the dynamic problem equations. We also hint at the study of the convergence of the solution to the dynamic problem to that to the quasi-static problem as a small parameter – the ratio of the largest propagation speed for an elastic wave in the body to the speed of light – tends to zero. (10.1142/S0218202515500578)
  DOI : 10.1142/S0218202515500578
• A Reduced Integration for Reissner-Mindlin Non-linear Shell Analysis Using T-Splines
  
  • Adam Cédric
  • Bouabdallah Salim
  • Zarroug Malek
  • Maitournam Habibou
  , 2015, Lecture Notes in Computational Science and Engineering (107), pp.103-125. We propose a reduced shell element for Reissner-Mindlin geometric non-linear analysis within the context of T-spline analysis. The shell formulation is based on the displacements and a first order kinematic in the thickness is used for the transverse shear strains. A total Lagrangian formulation is considered for the finite transformations. The update of the incremental rotations is made using the quaternion algebra. The standard two-dimensional reduced quadrature rules for structured B-spline and NURBS basis functions are extended to the more flexible T-meshes. The non-uniform Gauss-Legendre and patchwise reduced integrations for quadratic shape functions are both presented and compared to the standard full Gauss-Legendre scheme. The performance of the element is assessed with linear and geometric non-linear two-dimensional problems in structural analysis. The effects of mesh distortion and local refinement, using both full and reduced numerical quadratures, are evaluated. (10.1007/978-3-319-23315-4_5)
  DOI : 10.1007/978-3-319-23315-4_5
• Du Sel au Diamant: Minéraux en fluage à tous les étages !
  
  • Dimanov Alexandre
  , 2015.
• An analytical model for porous single crystals with ellipsoidal voids
  
  • Mbiakop Armel
  • Constantinescu Andrei
  • Danas Kostas
  Journal of the Mechanics and Physics of Solids, Elsevier, 2015, 84, pp.436-467. A rate-(in)dependent constitutive model for porous single crystals with arbitrary crystal anisotropy (e.g., FCC, BCC, HCP, etc.) containing general ellipsoidal voids is developed. The proposed model, denoted as modified variational model (MVAR), is based on the nonlinear variational homogenization method, which makes use of a linear comparison porous material to estimate the response of the nonlinear porous single crystal. Periodic multi-void finite element simulations are used in order to validate the MVAR for a large number of parameters including cubic (FCC, BCC) and hexagonal (HCP) crystal anisotropy, various creep exponents (i.e., nonlinearity), several stress triaxiality ratios, general void shapes and orientations and various porosity levels. The MVAR model, which involves a priori no calibration parameters, is found to be in good agreement with the finite element results for all cases considered in the rate-dependent context. The model is then used in a predictive manner to investigate the complex response of porous single crystals in several cases with strong coupling between the anisotropy of the crystal and the (morphological) anisotropy induced by the shape and orientation of the voids. Finally, a simple way of calibrating the MVAR with just two adjustable parameters is depicted in the rate-independent context so that an excellent agreement with the FE simulation results is obtained. In this last case, this proposed model can be thought as a generalization of the Gurson model in the context of porous single crystals and general ellipsoidal void shapes and orientations. (10.1016/j.jmps.2015.07.011)
  DOI : 10.1016/j.jmps.2015.07.011
• Carbon nanotubes sensors for sustainable city: prototyping, integration, reliability and deployment
  
  • Michelis Fulvio
  • Bodelot Laurence
  • Bonnassieux Yvan
  • Lebental Bérengère
  , 2015, pp.13p. While today's galloping urbanization weighs heavily on both People and Environment and while Climate Change increases natural risks worldwide, Internet of Things Technologies stand at the forefront of the efforts toward Greener Cities. Nanosensors fully integrated into wireless sensor node may become instrumental in this field because of their small size, low cost, versatility and low power consumption. Potential applications are environmental monitoring, structural health monitoring, energy performances monitoring or people exposure monitoring. Challenges range from the manufacturing of the sensors with high reproducibility to their full integration into communicating devices, including ensuring device reliability in complex and harsh environmental conditions. Carbon nanotubes (CNT) especially are choice material toward this goal, as they have demonstrated both a very strong sensitivity to a variety of environmental parameters and a strong resilience to chemical and mechanical stress. In the present paper, we present a full proof of concept of the use of carbon nanotubes sensors for urban applications, from the manipulation of the carbon nanotubes to the application of the sensors in real life. Two specific examples are discussed, infrastructure durability monitoring and water quality monitoring. Specific methodologies for reliability analysis of carbon-based nanomaterials are also discussed.
• Bacillus subtilis Bacteria generate an Internal Mechanical Force within a Biofilm
  
  • Douarche Carine
  • Allain Jean-Marc
  • Raspaud Eric
  Biophysical Journal, Biophysical Society, 2015.
• Modelling complex high speed multimaterial evolutions using a single mesh multivelocity strategy
  
  • Folzan Gauthier
  • Le Tallec Patrick
  • Perlat Jean-Philippe
  International Journal for Numerical Methods in Engineering, Wiley, 2015, 104 (7), pp.539–565. In the present paper, we propose another space discretization of the kinematic constraint for a single grid multi velocity formulation leading to a better approximation of the interface physics. The paper is organized as follows. In the next section, we will briefly review the problem to solve and the single mesh multi-velocity discretization strategy. In Section 3, we will then introduce our new cell-based discretization of the normal velocity continuity constraint on the interface, develop the proper velocity enrichment, and analyse its stability. A generic time discretization is next introduced in Section 4 and adapted to the specific space discretization proposed herein. The proposed methodology is finally validated on a few numerical examples. (10.1002/nme.4827)
  DOI : 10.1002/nme.4827
• Dissipative Homogenised Reinforced Concrete (DHRC) constitutive model dedicated to reinforced concrete plates under seismic loading
  
  • Combescure Christelle
  • Dumontet Hélène
  • Voldoire François
  International Journal of Solids and Structures, Elsevier, 2015, 73-74, pp.78 - 98. A new stress resultant nonlinear dissipative constitutive model for reinforced concrete (RC) plates under cyclic solicitations is presented. This constitutive model, named DHRC for Dissipative Homogenised Reinforced Concrete, is expressed within the usual thin plate kinematics framework. It is built by a periodic homogenisation approach using the averaging method and it couples concrete damage and periodic debonding between steel rebar and surrounding concrete. The generality of the proposed method leads to a generic closed-form for the Helmholtz strain energy density function and the two dissipation pseudo-potentials that can be adapted to any material with an internal structure similar to the RC structural element one. A restricted number of geometric and material characteristics are needed from which the whole set of model parameters are identified through an automatic numeric procedure performed on a Representative Volume Elements (RVEs) of the RC plate. Finally, comparisons of finite element simulations with experimental results concerning the seismic behaviour of reinforced concrete wall made structures are proposed and discussed. (10.1016/j.ijsolstr.2015.07.007)
  DOI : 10.1016/j.ijsolstr.2015.07.007
• On the efficiency and robustness of damping by branching
  
  • Théckès Benoit
  • Boutillon Xavier
  • de Langre Emmanuel
  Journal of Sound and Vibration, Elsevier, 2015, 357. This paper investigates the mechanism referred to as clamping by branching (DBB), and its ability to attenuate the response of an oscillating structure, in the range of large amplitudes. More specifically, we give an experimental proof of this mechanism and we show that it is very robust against variations of the physical parameters and constituents: nature of the damping mechanism, geometrical structure. These results motivated the design of the Tuned Mass Branched Damper (TMBD) which is shown to be a little more efficient than the classical Tuned Mass Damper (TMD) in some domains of the parameter space. (10.1016/j.jsv.2015.07.018)
  DOI : 10.1016/j.jsv.2015.07.018
• Influence of process-induced microstructure on hardness of two Al-Si alloys
  
  • Tabibian Shadan
  • Charkaluk Eric
  • Constantinescu Andrei
  • Guillemot Gildas
  • Szmytka Fabien
  Materials Science and Engineering: A, Elsevier, 2015, 646, pp.190-200. This paper analyses the influence of thermal-induced aging on the strength of cast A319 and A356 aluminum alloys. This phenomena is of primary importance especially in the automotive industry, where on one hand the alloys experience Thermo-Mechanical and Low Cycle Fatigue loading conditions and on the other hand their microstructure is induced both by the manufacturing process and the thermal histories. The alloys studied here were produced using an industrial Lost Foam Casting process which affects significantly the microstructure and the precipitation compared to standard Die Casting process. The paper compares mechanical properties of these peculiar alloys in terms of microhardness at the macroscopic level as a function of thermal overaging time and at the microscopic level in terms of properties of the different phases (intermetallics, eutectics) present in the microstructure. Important differences can be observed between these different phases and the results are consistent with similar studies from the literature on different aluminum alloys and processes. (10.1016/j.msea.2015.08.051)
  DOI : 10.1016/j.msea.2015.08.051
• Fatigue of Metallic Stents: From Clinical Evidence to Computational Analysis
  
  • Auricchio Ferdinando
  • Constantinescu Andrei
  • Conti Michele
  • Scalet Giulia
  Annals of Biomedical Engineering, Springer Verlag, 2015, pp.1-15. The great success of stents in treating cardiovas-cular disease is actually undermined by their long-term fatigue failure. The high variability of stent failure incidence suggests that it is due to several correlated aspects, such as loading conditions, material properties, component design, surgical procedure, and patient functional anatomy. Numerical and experimental non-clinical assessments are included in the recommendations and requirements of several regulatory bodies and they are thus exploited in the analysis of stent fatigue performance. Optimization-based simulation methodologies have been developed as well, to improve the fatigue endurance of novel designs. This paper presents a review on the fatigue issue in metallic stents, starting from a description of clinical evidence about stent fracture up to the analysis of computational approaches available from the literature. The reported discussion on both the experimental and numerical framework aims at providing a general insight into stent lifetime prediction as well as at understanding the factors which affect stent fatigue performance for the design of novel components. (10.1007/s10439-015-1447-8)
  DOI : 10.1007/s10439-015-1447-8
• Application of the Dugdale model to a mixed mode loading of a semi infinite cracked structure
  
  • Ferdjani Hichème
  • Marigo Jean-Jacques
  European Journal of Mechanics - A/Solids, Elsevier, 2015, 53, pp.1-9. The Dugdale model was initially developed in the case of a mode I loading. It was extended to other modes and to the mixed mode case. The exact solutions were given for all these modes in the case of an infinite medium with a straight crack. This work is an application of the Dugdale model to a crack in a semi infinite structure submitted to a mixed mode loading. The coupled system of singular integral equations of the first kind corresponding to the elastostatic problem is solved semi-analytically. Particular attention is needed in the resolution because of jump discontinuities in the loading of the crack faces. The criteria of propagation are deduced from the revisited Griffith theory <a href="https://hal.archives-ouvertes.fr/hal-03500962v1">(Francfort, Marigo, Journal of Mechanics and Physics of Solids, 1998)</a>. The presented results show the evolution of the applied load and critical stress with the crack length. The shape of the crack gap is also presented. A comparison with the problem of a crack in an infinite structure is performed. (10.1016/j.euromechsol.2015.02.006)
  DOI : 10.1016/j.euromechsol.2015.02.006
• Piezoresistivity of thin film semiconductors with application to thin film silicon solar cells
  
  • Lange D.
  • Cabarrocas P.Roca I
  • Triantafyllidis N.
  • Daineka D.
  Solar Energy Materials and Solar Cells, Elsevier, 2015. (10.1016/j.solmat.2015.09.014)
  DOI : 10.1016/j.solmat.2015.09.014
• Stable time step estimates for NURBS-based explicit dynamics
  
  • Adam Cédric
  • Bouabdallah Salim
  • Zarroug Malek
  • Maitournam Habibou
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2015, 295, pp.581–605. Automobile crashworthiness is a complex application for numerical methods in dynamics of structures which includes many high non-linearities. Explicit techniques are widely used for structural dynamics dealing with difficult and large problems that prevent the use of implicit methods. We propose, in this paper, a deep study of the stable time step, which guarantees the stability of the method, and its estimates, for one-dimensional and two-dimensional problems. Element and nodal time steps are presented and adapted to highly regular B-spline and NURBS functions, in the context of isogeometric analysis. The size of the proposed stable time estimates benefits from the properties of regularity and extended support of the basis. Their performance is assessed and compared in several examples, with an arbitrary mesh, uniform or non-uniform, and considering polynomial orders from one to five. The smoothness and order of the polynomials have a significant effect on the stable time step and its estimates. Several lumping schemes of the mass matrix are presented and their accuracy is assessed. (10.1016/j.cma.2015.03.017)
  DOI : 10.1016/j.cma.2015.03.017
• Numerical and experimental investigation of Lüders bands propagation
  
  • Baudoin Pierre
  • Mazière Matthieu
  • Witz Jean-Francois
  • Magnier Vincent
  • El Bartali Ahmed
  • Dufrenoy Philippe
  • Forest Samuel
  • Charkaluk Eric
  • Demilly F.
  , 2015.
• Characterization and analysis of deformation heterogeneities in commercial purity titanium
  
  • Barkia B
  • Doquet Véronique
  • Héripré E
  • Guillot I
  Materials Characterization, Elsevier, 2015 (108), pp.94-101. The effects of solute oxygen, loading direction and strain level on the microscale plastic strain distribution in representative areas of commercially-pure titanium have been characterized by correlation of high resolution SEM images captured during in situ tensile tests. A spatial organization of highly-deformed bands was observed from the early stages of plastic flow and remained nearly unchanged as the materials were strained. The high strains close to grain boundaries were related to intense local slip activity, grain boundary sliding or kink bands formation. The plastic strain field was more homogeneous in the oxygen-rich material, which was attributed primarily to a smaller contribution of grain boundary sliding, due to the presence of hard β phase particles along the grain boundaries. (10.1016/j.matchar.2015.09.001)
  DOI : 10.1016/j.matchar.2015.09.001
• Homogénéisation non linéaire des matériaux poreux monocristallins: Modélisation, implémentation numérique et applications au fluage et à la fatigue
  
  • Armel Mbiakop
  , 2015. Ce travail de thèse porte sur le développement d'un modèle constitutif viscoplastique pour monocristaux poreux à structure cristalline arbitraire et microstructures ellipsoïdales. Le modèle proposé, appelé modèle variationel modifié (MVAR), est basé sur la méthode d'homogénéisation variationelle non linéaire, qui utilise un composite linéaire de comparaison pour estimer la réponse non linéaire du monocristal poreux. Par conséquent, l'objectif principal de cette étude est de proposer un modèle constitutif général prenant en compte l'évolution de la microstructure et l'anisotropie induite quand le monocristal poreux est sollicité en déformations finies. En outre, des simulations EF périodiques sont utilisées pour valider le MVAR pour un grand nombre de paramètres incluant l'anisotropie cristalline cubique (FCC, BCC) et hexagonale (HCP), plusieurs exposants de uage (i.e. non linéarité), différentes triaxialités, angles de Lode, formes et orientations de pores et plusieurs niveaux de porosité. Le MVAR est en bon accord avec les résultats EF pour tous les cas considérés dans cette étude. Il est ensuite utilisé pour investiguer la réponse mécanique complexe des monocristaux poreux sous differentes conditions avec notammant le très fort couplage entre l'anisotropie cristalline et l'anisotropie morphologique induite par la forme et l'orientation des pores. De plus, une approche nouvelle de calibration avec seulement deux paramètres ajustables est proposée de manière à obtenir un excellent accord entre modèle et simulations. Par ailleurs, un modèle de Tresca poreux est dérivé par le biais d'une approche originale se servant du modèle pour monocristaux poreux et considérant le cas limite d'un nombre infini de systèmes de glissements (qui conduit au critère de Tresca). Enfin, les différents résultats sus-mentionnés sont étendus afin de prendre en compte l'évolution de la microstructure quand le matériau est sollicité en déformations finies.
• Synthesis of an Artificial Cornea Allowing In Vitro Colonization of the Host Cells
  
  • Tidu Aurelien
  • Ghoubay-Benallaoua D.
  • Teulon C.
  • Lynch Barbara
  • Haye Bernard
  • Illoul Corinne
  • Allain Jean-Marc
  • Borderie V.
  • Schanne-Klein Marie-Claire
  • Mosser G.
  , 2015, 21, pp.S142-S142.
• Modélisation du comportement viscoélastique d'un élastomère fortement chargé sous sollicitations multiaxiales
  
  • Jalocha Dimitri
  , 2015. Le propergol composite est un élastomère fortement chargé utilisé dans les moteurs à propulsion solide. Garantir la fiabilité d’un tel moteur repose sur la bonne connaissance des propriétés mécaniques de ses constituants. Malgré son fort taux de charge, le comportement du propergol est viscoélastique, mais présente de nombreuses non linéarités. L’étude menée ici se concentre sur l’influence de la déformation statique sur les propriétés visqueuses du composite. L’objectif est de caractériser cette non linéarité, la modéliser, l’implémenter dans un outil de simulation numérique et déterminer son influence sur la réponse générale d’un moteur à propulsion solide soumis à une sollicitation dynamique. Afin d’atteindre cet objectif, les travaux se divisent en plusieurs étapes. La première consiste à déterminer à l’échelle microscopique les causes des phénomènes non linéaires observables à l’échelle macroscopique. Puis les propriétés viscoélastiques sont caractérisées, en fonction de la déformation statique. Cette étape expérimentale est réalisée à la fois dans le domaine temporel et dans le domaine fréquentiel, et ce sous des sollicitations uni axiales et bi axiales. Pour ce faire, une machine de traction dynamique bi axiale est développée. Puis un modèle non linéaire continu est identifié sur l’ensemble des résultats obtenus, permettant de reproduire à la fois les effets du temps mais également les effets de la déformation statique sur les propriétés mécanique. Ce modèle continu est discrétisé en vue d’être implémenté dans une loi de comportement viscoélastique non linéaire, permettant de donner une relation entre la déformation appliquée dans un matériau et la contrainte générée. Ce modèle est introduit dans un code éléments finis. Pour déterminer l’influence de la non linéarité engendrée par la déformation statique, une simulation est réalisée sur un modèle de moteur à propulsion solide. Les propriétés du propergol le constituant sont successivement modélisées par un comportement linéaire et non linéaire (développé dans ces travaux). Les deux réponses sont comparées et indiquent l’importance de ne pas négliger l’impact de l’effet engendré par la déformation statique, ainsi que la nécessité de modéliser finement le comportement du propergol. De manière analogue, un travail de modélisation pourrait être poursuivit en essayer de prendre en compte cette fois ci la partie dynamique de la déformation sur les propriétés du composite.
• Multiscale biomechanics of skin: experimental investigation of the role of the collagen microstructure
  
  • Lynch Barbara
  , 2015. Skin is a complex organ consisting of three main layers, namely the epidermis, dermis and hypodermis. The dermis is responsible for most of the complex mechanical properties of skin, including non-linearity, anisotropy and viscoelasticity. Like all soft collagenous tissues, the dermis is constituted mostly of extracellular matrix proteins, fibrillar collagens being the major structural components. Modelling efforts using a scaling-up approach for skin generally lack appropriate micro-mechanical experiments to clarify the link between macroscopic mechanical properties and microstructural behaviour. The goal of this research was to measure the evolution of skin's microstructure during mechanical stimulation to identify the relevant mechanisms at the microscopic scale. Uniaxial tensile tests were carried out on ex vivo mice skin under a multiphoton microscope with Second Harmonic Generation detection. This technique allows for specific imaging of collagen fibres in the depth of the dermis. We were then able to simultaneously monitor the tissue's mechanical response and image the microstructural reorganisation of the fibrillar collagen network, using quantitative characterisations at both scales. We showed that the collagen fibres continuously align in the direction of traction with stretch, generating the observed mechanical response. A general framework of hypothetical microstructural mechanisms was proposed to account for the features observed experimentally. Genetic mutations inducing a decreased or abnormal collagen synthesis can result in defective mechanical properties in skin. For instance, patients suffering from Ehlers-Danlos syndrome, a general collagenous tissue disorder caused by mutations in the genes coding for a minor form of collagen, typically present hyperelastic skin. We applied our multiscale approach to two genetically-modied mice strains created in the context of investigating the Ehlers-Danlos syndrome. The ageing process is also a factor of change in skin's mechanical properties, and was investigated in this work through experiments on aged mice skin. Genetically-modied and aged mice skin exhibited altered collagen reorganisation and mechanical response during a tensile test. The variations were interpreted in the context of the microstructural interpretation developed for control mice, and can be used for phenotyping. These findings show that our multiscale approach provides new crucial information on the biomechanics of skin. It can be generalised to study other pathologies, other collagenous tissues, or other mechanical properties, such as the biaxial or viscoelastic response.
• Ductile fracture of aluminum 2024-T351 under proportional and non-proportional multi-axial loading: Bao–Wierzbicki results revisited
  
  • Papasidero Jessica
  • Doquet Véronique
  • Mohr Dirk
  International Journal of Solids and Structures, Elsevier, 2015, 69-70, pp.459-474. The effect of stress state and loading path on the ductile fracture of aluminum 2024-T351 is characterized through tension–torsion experiments on tubular specimens. The experimental program includes proportional and non-proportional loading paths leading to the onset of fracture at nearly plane stress conditions at stress triaxialities between 0 and 0.6. Stereo digital image correlation is used to measure the displacements and rotations applied to the specimen shoulders. An isotropic non-quadratic Hosford plasticity model with combined Voce–Swift hardening is used to obtain estimates of the local stress and strain fields within the specimen gage section. The hybrid experimental–numerical results indicate a higher strain to fracture for pure shear than for uniaxial tension. The calibration of a Hosford–Coulomb fracture initiation model suggests that the ductility of aluminum 2024-T351 decreases monotonically as a function of the stress triaxiality, whereas it is a non-symmetric convex function of the Lode angle parameter. It is shown that a simple non-linear damage accumulation rule can describe the effect of non-proportional loading on the strain to fracture. (10.1016/j.ijsolstr.2015.05.006)
  DOI : 10.1016/j.ijsolstr.2015.05.006
• Experimental evaluation of contact stress during cold rolling process with optical fiber Bragg gratings sensors measurements and fast inverse method
  
  • Weisz-Patrault Daniel
  • Maurin Laurent
  • Legrand Nicolas
  • Ben Salem Anas
  • Ait Bengrir Abdelkebir
  Journal of Materials Processing Technology, Elsevier, 2015, 223, pp.105-123. There is a strategic importance for the steel rolling industry to get a better understanding of the strip–roll interaction to improve roll-gap models, increase strip quality and decrease roll degradation. This requires roll-gap sensors able to measure this interaction under industrial rolling conditions and in real time in order to propose a feed-back control of process parameters. To reach these goals, this paper proposes a new roll-gap friction sensor based on an inverse method that interprets optical fiber Bragg gratings(FBG) strain measurements under the roll surface (fully embedded), which enables to evaluate contact stresses with very short computation times, compatible with real time interpretation. This elastic inverse method is analytical and relies on plane-strain and isothermal assumptions. The experimental apparatus is detailed, technical issues are clearly exposed as well as calibration procedures. Several pilot cold rolling tests have been performed at various rolling speeds and different strip thicknesses in order to demonstrate the industrial feasibility. Resulting evaluations of contact stresses are then compared with numerical simulations. Reasonable agreement is obtained for normal stress (i.e., pressure) but not for shear stress(only an order of magnitude is obtained). (10.1016/j.jmatprotec.2015.03.047)
  DOI : 10.1016/j.jmatprotec.2015.03.047
• Huy Duong Bui
  
  • Salençon Jean
  • Zaoui André
  Journal of Mechanics of Materials and Structures, Mathematical Sciences Publishers, 2015, 10 (3), pp.207-217. Huy Duong Bui, member of the French Academy of Sciences, passed away on May 29, 2013 at the age of 76. He was a founding member of the French Academy of Technologies, a member of the European Academy of Sciences and a Fellow of the Institute of Physics (London). He was also a Knight in the French Ordre national de la Légion d’honneur... (10.2140/jomms.2015.10.207)
  DOI : 10.2140/jomms.2015.10.207
• Curvature of an elasto-plastic strip at finite strains : application to fast simulation of coils
  
  • Weisz-Patrault Daniel
  • Ehrlacher Alain
  , 2015. This work is part of the framework of a fast modeling of winding aiming at improving knowledge of residual stress evolution in steel strips and therefore their flatness during the coiling process. An exact analytical solution of an elasto-plastic strip with isotropic hardening at finite strains under an imposed transformation of curvature is developed. Issues related to flow rules for non-differentiable yield functions (Tresca) have been broached and a unique solution is obtained. The equivalence for this transformation, between von Mises and Tresca yield functions is demonstrated. This solution contributes to an efficient model by terms of computation times that aims at simulating coiling by taking into account inelastic deformations and enabling parametric studies in order to improve the process.
• Caractérisation du comportement mécanique d'un gradient de microstructure
  
  • Baudoin Pierre
  • Magnier Vincent
  • El Bartali Ahmed
  • Witz Jean-François
  • Philippe Dufrénoy
  • Charkaluk Eric
  • Demilly François
  , 2015. Une démarche pour la caractérisation des métaux à gradients de microstructure s'appuyant sur des mesures de champs cinématiques est proposée. L'application d'un traitement de recristallisation à une éprouvette de traction en fer pur permet l'obtention d'un gradient de taille de grain localisé. Une variation de propriétés élasto-plastique à l'échelle de ce gradient de microstructure est recherchée en comparant la réponse observée aux résultats de calculs éléments finis.