MICROMECHANICAL DAMAGE MODEL TAKING LOADING-INDUCED ANISOTROPY INTO ACCOUNT

This paper deals with a micromechanical damage model, based on a const itutive theory for brittle materials weakened by microcracks. The mode l is implemented in the DYNA3D three-dimensional explicit finite eleme nt code. The phenomenological study shows the importance of taking mic romechanical effects into account to model macroscopic failure of the material. The constitutive model relates damage to microscopic paramet ers (size of microcracks, cracks density etc.) and takes loading-induc ed anisotropy damage into account by correlating microcrack growth to preferential orientations. The unilateral character (behaviour differe nce between tension and compression) is treated by the microcrack grow th criterion. The progressive reduction in material stiffness due to t he presence of microcracks is modelled using Margolin's effective modu lus expressions, and the material is pulverised if the microcrack dens ity exceeds a critical value. Determination of the energy dissipated b y damage is proposed. The constitutive model applied to SiC/SiAlYON ce ramics is validated by a comparaison of the results between a Hopkinso n's Bar Test and numerical simulation. Comparing the macroscopic britt le model results with the damage model results shows the ability of th e second to predict microcrack effects on the dynamic failure behaviou r of ceramics.