Micromechanical damage model taking loading-induced anisotropy into account

Abstract

This paper deals with a micromechanical damage model, based on a constitutive theory for brittle materials weakened by microcracks. The model is implemented in the DYNA3D three-dimensional explicit finite element code. The phenomenological study shows the importance of taking micromechanical effects into account to model macroscopic failure of the material. The constitutive model relates damage to microscopic parameters (size of microcracks, cracks density etc.) and takes loading-induced anisotropy damage into account by correlating microcrack growth to preferential orientations. The unilateral character (behaviour difference between tension and compression) is treated by the microcrack growth criterion. The progressive reduction in material stiffness due to the presence of microcracks is modelled using Margolin's effective modulus expressions, and the material is pulverised if the microcrack density exceeds a critical value. Determination of the energy dissipated by damage is proposed. The constitutive model applied to SiC/SiAlYON ceramics is validated by a comparaison of the results between a Hopkinson's Bar Test and numerical simulation. Comparing the macroscopic brittle model results with the damage model results shows the ability of the second to predict microcrack effects on the dynamic failure behaviour of ceramics.