Publications

2012

• A new model of damage: a moving thick layer approach
  
  • Stolz Claude
  • Moes Nicolas
  International Journal of Fracture, Springer Verlag, 2012, 174 (1), pp.49-60. A new formulation of a damage law is proposed based on a continuous transition between a sound material and a totally or partially broken material. The evolution of damage is then associated with a moving layer. This point of view permits the description of initiation and propagation of defects in an unified framework. The motion of the thick layer is defined in the frame of the moving surface I" (o) separating the sound material and the damaged material. When the damage parameters are continuous functions of the distance to I" (o) , they satisfy the conditions of transport. For particular geometries and loadings the evolution of the system is discussed. Comparison with description of damage with discontinuities and sharp interface is also presented. (10.1007/s10704-012-9693-3)
  DOI : 10.1007/s10704-012-9693-3
• Dehydration-induced damage and deformation in gypsum and implications for subduction zone processes
  
  • Brantut Nicolas
  • Shubnel Alexandre
  • David Christian
  • Héripré Eva
  • Gueguen Yves
  • Dimanov Alexandre
  Journal of Geophysical Research, American Geophysical Union, 2012, 117 (B3). Experimental heating tests were performed on Volterra gypsum to study the micromechanical consequences of the dehydration reaction. The experimental conditions were drained, at 5~MPa fluid pressure, and confining pressures ranging from 15 to 55 MPa. One test was performed with a constant applied differential stress of 30~MPa. The reaction is marked by (1) a porosity increase and homogeneous compaction, (2) a swarm of acoustic emissions, (3) a large decrease in P- and S-wave velocities, and (4) a decrease in VP/VS ratio. Wave velocity data are interpreted in terms of crack density and pore aspect ratio, which, modeling pores as spheroids, is estimated at around 0.05 (crack-like spheroid). Complementary tests performed in an environmental scanning electron microscope indicate that cracks first form inside the gypsum grains, and are oriented preferentially along the crystal structure of gypsum. Most of the visible porosity appears at later stages when grains shrink and grain boundaries open. Extrapolation of our data to serpentinites in subduction zones suggest that the signature of dehydrating rocks in seismic tomography could be a low apparent Poisson's ratio, although this interpretation may be masked by anisotropy development due to preexisting crystal preferred orientation and/or deformation-induced cracking. The large compaction and the absence of strain localization in the deformation test suggests that dehydrating rocks may be seen as soft inclusions and could thus induce ruptures in the surrounding, nonreacting rocks. (10.1029/2011JB008730)
  DOI : 10.1029/2011JB008730
• Experiments and Modeling of Anisotropic Aluminum Extrusions under Multi-axial Loading - Part II: Fracture
  
  • Dunand M.
  • Luo Meng
  • Mohr Dirk
  International Journal of Plasticity, Elsevier, 2012, pp.36-58.
• Various estimates of Representative Volume Element sizes based on a statistical analysis of the apparent behavior of random linear composites
  
  • Salmi Moncef
  • Auslender François
  • Bornert Michel
  • Fogli Michel
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2012, 340 (4-5), pp.230-246. This article aims at proposing various estimates of the size of the Representative Volume Element (RVE) of random linear elastic matrix-inclusion composites. These estimates are derived from the computation of the apparent behavior of finite size volume elements (VE) by a new procedure presented in . [18] by Salmi et al. (2012) and briefly recalled. Two different points of view to define an RVE are considered: the RVE is defined as being the smallest VE required either to evaluate numerically the considered effective property of the composite by appropriate statistical averaging of apparent ones, or to be allowed to replace any instance of the heterogeneous material by a unique homogeneous equivalent one in structural mechanics problems. In order to introduce the fluctuations of the apparent properties within such definitions of the RVE size, we first study the statistics of the apparent properties. Then, relying on the results of this statistical study, several proposals of RVE criteria are presented and applied to random linear elastic fiber-matrix composites for several contrasts and inclusion (or pore) volume fractions. © 2012 Académie des sciences. (10.1016/j.crme.2012.02.007)
  DOI : 10.1016/j.crme.2012.02.007