Isotropic damage model based on a tensorial representation of damage

A 3-D phenomenological model of isotropic damage is developed for brittle solids based on the effective stress concept. The shortcomings of the commonly used scalar variable, as representative of isotropic damage, are discussed. It is shown that isotropic damage is best represented by an isotopic tensor of rank four. The damage evolution law is postulated using strain tensor invariants, based on decomposition of strain energy. The model is tested with experimental results for two cases: uniaxial compression of quartzite rock and uniaxial tension of a quasi-isotropic graphite-epoxy laminated composite. Simulations and experimental results show that Poisson's ratio increases in both cases.