複数の双晶系の活動を考慮した六方晶金属の結晶塑性モデリング

抄録

Deformation twinning is an important deformation mechanism of metallic materials as well as slip deformation, especially in hexagonal closed-packed (HCP) metals such as magnesium and titanium. Therefore, understanding twinning behavior is essential to improve mechanical properties of HCP metals. HCP metals generally have a strong anisotropy in crystalline scale. For example, in case of magnesium, plastic deformation due to slip along the c-axis is hard to occur because of much higher critical resolved shear stress of pyramidal slip system, and deformation twinning occur to enhance plastic deformation along the c-axis. The most dominant twinning in magnesium is {1012}〈1120〉 tensile twinning system, the number of which is six. As several experimental results showed that untwinned and twinned regions can simultaneously exist in a grain, a crystal plasticity model considering the volume fraction of deformation twinning was proposed. In the practical problems, multiple twinning systems may be simultaneously activated in a grain because of inhomogeneity of deformation. Therefore, in this study, the crystal plasticity model considering the volume fraction of deformation twinning is extended to incorporate the volume fraction of multiple twinning systems. Numerical investigations using the crystal plasticity finite element method are performed and the adequacy of the model is validated.