Plastic Flow Direction of Polycrystalline Magnesium

Abstract

A quantitative evaluation of the subsequent yield behavior of a polycrystalline magnesium, which is a typical hexagonal metal, based on the crystal plasticity model is presented. The non-normality effect, that is, the difference between the normal to the yield surface and the plastic flow direction under a non-proportional loading condition, is numerically investigated, and it is shown that the non-normality effect of polycrystalline magnesium is stronger than that of cubic metals. Additionally, the intensity of the non-normality of hexagonal metals depends on the amplitude of the offset strain, which is the pre-strain before non-proportional loading, while that of cubic metals is almost constant with respect to the offset strain. The contribution of each slip system to the non-normality effect is investigated. It is clarified that the difficulty of switching the dominant slip system when the strain path changes plays an important role and is the principal mechanism behind the strong non-normality effect of polycrystalline magnesium. The effect of the initial texture on the non-normality effect is also discussed.

Fig. 2 Stress paths on σ₁₁ − σ₂₂ plane. Green solid and red dashed lines indicate directions of plastic deformation rate and the normal to the subsequent yield surface. Stress path for the four different offset strains of ε-^p = 0.5%, 1.0%, 5.0% and 10.0% are illustrated.