Steady states in severe plastic deformations and microstructure at normal and high pressure

Abstract

The main fundamental problem in studying plasticity and microstructure evolution is that they depend on five components of the plastic strain tensor εp, its entire path and pressure p and its path p-path, which leaves little hope of finding some general laws, especially at severe plastic straining and high pressures. Here, we review the validity of the following hypothesis for quasi-static material behavior after some critical level of cold severe plastic strain and some straining paths: initially isotropic polycrystalline materials behave like perfectly plastic, isotropic, and strain-path-independent with the corresponding limit surface of perfect plasticity and reach steady values of the crystallite/grain size and dislocation density, which are strain- and strain-path-independent. However, there are multiple steady microstructural states and corresponding limit surfaces of perfect plasticity. The main challenge is to find for which classes of loading paths and p-path material behaves along the same limit surface of perfect plasticity and steady microstructural state and for which loading paths and p-path there is a jump to the different limit surface of perfect plasticity and steady microstructural state. Various experimental, computational, and coupled experimental-computational techniques are analyzed, and some controversies and challenges are summarized.