Modeling microdefects closure effect with isotropic/anisotropic damage

Continuum damage mechanics (CDM) for metals is often written in terms of an isotropic ( scalar) damage. In this case, solutions have been proposed to represent the differences of behavior in tension and in compression also called quasi- unilateral (QU) conditions or microdefects closure effect. A recent anisotropic damage model has been developed to take into account the damage orthotropy induced by plasticity (Lemaitre, J., Demorat R. and Sauzay, M. ( 2000). Anisotropic Damage Law of Evolution, Eur. J. Mech. A/Solids, 19: 513-524). The purposes here are then two. First, a unified framework for isotropic and anisotropic damage is proposed. Then, it is to extend Ladeve` ze and Lemaitre's framework (Ladeveze, P. and Lemaitre, J. (1984). Damage Effective Stress in Quasi Unilateral Conditions, In: Proceedings of the 16th International Congress of Theoretical and Applied Mechanics, Lyngby, Denmark) for the QU conditions to anisotropic damage induced by plasticity. Yield surfaces and damage versus accumulated plastic strain curves, drawn for different loading, illustrate the effect of the QU conditions on the damage evolution.