Damage is conventionally defined as the progressive deterioration of materials due to nucleation and growth of microcracks. The purpose of the damage concept [1] is to take into account the microscopic deterioration of the material in its macroscopic constitutive law. In composite materials, the microcracks have a preferential orientation and the damage variable depends on the direction of measurement [2]. Non linear analysis of such materials must consider this anisotropy by introducing a tensorial damage variable in the constitutive equations [3]. The main difficulties when dealing with anisotropic description of damage are to be able to identify the introduced parameters [4].