Damage modeling at two scales for 4D carbon/carbon composites

Damage mechanisms and inelastic mechanical phenomena are modeled to the macroscopic scale for multiaxial loading. The studied material made by Société Européenne de Propulsion (SEP) is a 4D carbon–carbon (C/C) composite comprising four reinforcement directions. A very simple mathematical material model has been first derived for multiaxial loading as a consequence of some remarkable experimentally observed properties and the material geometry. The anisotropic continuum damage theory introduced by Ladevèze is used. To identify the material constants and functions characterizing the studied 4D C/C material is a rather difficult task: fiber debonding near the edges is very important for tensile tests. This is due to an edge effect, which modifies the local distribution of the stresses near a free surface. The study of this phenomenon is made at a mesoscopic scale with three constituents: the fibers, the matrix and the interfaces. A non-linear-damage model is introduced for the interface. Large scale FE calculations are done using special numerical methods adapted to such problems: a domain decomposition approach is associated with the LAnge Time INcrement (LATIN) method. Finally, the identified material model has been checked on various experiments.