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Cohesive zones models are commonly used in numerical simulations to take into account the onset and the propagation of microcracks leading to the fracture of materials. Their numerical implementation in finite element schemes is based on embedding surface traction-separation law between two adjacent bulk elements. The traction between two neighboring elements is linked to the corresponding opening by a cohesive relationship. The objective of the work reported here is to extend the approach developed in [1, 2] to identify the shape and parameters of the cohesive zone models in metal matrix composites with brittle inclusions and adapt this method to the study of initially heterogeneous material (e.g. graded metals or ceramics). To treat these applications where mechanical fields are heterogeneous, local stress fields are to be estimated in addition to conventional kinematic fields to build the energy balance associated with the transformation. Here we propose to estimate these fields by an identification method using kinematic and thermal data from imaging. The proposed method is based on the minimization of a functional associated with the error in constitutive relation (Constitutive equation gap method) [3]. In its classical (mechanical) formulation, this functional depends on two sets of parameters: the stress field and the mechanical material properties (elasticity, plasticity, damage). We show here that the identification procedure is capable to estimate the stress fields and material properties for elastic and elastoplastic behavior. The method was applied on noisy measured displacement fields to assess its robustness in the case of elastic behavior. The method is now being extended to damageable plasticity. The introduction of a second (calorimetric) term in the functional, related to the heat sources is also examined.

National audience; La déformation d'un matériau s'accompagne d'une variation de sa température. La détermination des sources volumiques ayant produites cette variation nous renseigne sur les processus de dissipation intrinsèque ainsi que les couplages présents au sein du matériau. Il est pour se faire nécessaire de relier le champ de température observé au cours de l'essai aux sources volumiques l'ayant engendré. Une méthode inverse adaptée à cette problématique est proposée dans cet article, la technique se base sur une extension au cas temporel de la méthode d'écart à la réciprocité. Sous certaines hypothèses le nombre de sources, leur position et leur énergie intégrée dans le temps sont retrouvées. La méthode bien que non-itérative présente une bonne stabilité vis-à-vis de mesures bruitées.See http://hal.archives-ouvertes.fr/docs/00/59/28/78/ANNEX/r_1UQW4I94.pdf

Colloque avec actes et comité de lecture. Internationale.; International audience; Dynamic sensitivity of a one-dimensional stack of four rigid blocks with controlled initial gaps, undergoing external harmonic vibrations is investigated. Time variation of the mass inertia and the relative kinetic energy are considered as dynamic block stack attributes. Numerical simulation is based on the Non Smooth Contact Dynamics (NSCD) time integration framework Solfec (http://code.google.com/p/solfec/). Sensitivity space parameters include a range of excitation frequencies and velocity amplitudes.