Development of a prediction system for CRSS ratio in polycrystalline metals

Abstract

Critical resolved shear stress (CRSS) determines the ease of slip deformation of metals. In crystal structures with low symmetry, such as the HCP structure, non-equivalent slip systems exist. CRSSs are different between the non-equivalent slip systems. The CRSS ratios between slip systems is an important factor governing the plastic deformation mechanism. Thus, methods for easily evaluating the CRSS ratios will play an important role to understand the deformation mechanism. In this study, we developed and validated a system to predict CRSS ratios for metal materials using spatial distributions of normal strain in the tensile direction and crystal orientation. The validation was performed by predicting CRSS ratios of HCP metals using the strain distributions which was obtained by crystal plasticity finite element analysis (CPFEM). The results showed that CRSS ratios were successfully predicted under conditions where multiple slip systems were activated, but in some cases the prediction failed. Investigating the cause of failure, we found that predictions failed under the following conditions: (i) only one slip system was active, (ii) distributions of Schmid factor for individual slip systems were similar to each other, and (iii) multiple slip systems were activated in the same region. We also proposed methods to solve the problems.

Keywords

• critical resolved shear stress
• normalized schmid factor
• crystal plasticity analysis
• hexiagonal close-packed structure
• prediction