Creep and plasticity of hexagonal polycrystals as related to single crystal slip

Abstract

The role of slip on basal, prismatic and pyramidal systems of hexagonal single crystals in determining inelastic polycrystalline behavior is studied using a uniform strain-rate upper bound and a self-consistent method. Steady power-law creep is considered. Included as a limiting case is rigid-perfectly plastic behavior, for which the upper bound to the yield stress of the polycrystal coincides with the Bishop-Hill bound for these materials. When the resolved shear stress needed to produce a given level of slip on the pyramidal systems is large compared to that on the other systems the upper bound lies well above the self-consistent estimate. Scif-consistent theory indicates that overall inelastic deformation of a polycrystal is possible without pyramidal slip. Implications for hexagonal materials, including ice, are discussed.