Geometrically characteristic kinetic thermodynamic deformation theory and intrinsic indices of the plasticity and damage of crystalline solid

A geometrically characteristic kinetic thermodynamic deformation theory is proposed for effective predictions over the full-life mechanical behaviour of crystalline solid. From a theoretic perspective, the proposed theory is distinguished from existing internal state variable theories at least in two aspects. Firstly, it is “geometrically characteristic” because the quantities employed for summarising the underlying defect status bear clear geometric meaning. An inelastic deformation status can be considered as the combination of two modes: a deviatoric mode resulting from the motion of distortional defects mainly underlying plasticity, and a volumetric mode resulting from the evolution of dilating defects likely giving rise to damage. Secondly, the proposed theory is said to be “kinetic”, because the mechanisms of underlying microstructural evolution impeded by local energy barriers are taken into account. A pair of material-intrinsic quantities measuring the hosting materials’ capabilities of resisting further inelastic deformation are then identified, which are employed as indices to assess the mechanical performance of crystalline solid. It is shown that conventional uniaxially loading data should suffice for calibrating the present theory, and this is in comparison with most existing ductile-damage models, where multi-triaxiality data seem necessary for calibration. The present theory, upon calibration against monotonic loading data, is also shown to be capable of describing non-monotonically loading situations, such as scenarios with cyclic loading and the phenomena of anisotropic plasticity.