High strain rate micro-compression for crystal plasticity constitutive law parameters identification

Abstract

Microcompression tests were performed on single crystal copper micropillars at 10−2 s−1 and 102 s−1 in the [100], [110] and [111] orientations, to provide inputs for crystal plasticity strain rate sensitive parameters inverse identification. The identification procedure used full pillar geometry finite element simulations. An identifiability indicator based on the cost function's hessian matrix approximate close to the minimum was used to assess the uniqueness and stability of the identified coefficients. Experimental microcompression tests displayed a strain rate sensitive behaviour in the [100] crystal orientation. The [110] and [111] orientations were less sensitive and were not used for identification. Stress-strain curve sensitivity plots revealed that the higher the strain rate, the better the sensitivity. This was attributed to high strain rates concentration in the shear bands as the strain rate increases. Identification on experimental data well represented the single crystal strain rate sensitivity in the [100] orientations. A unique solution was found using only a single orientation.

Keywords

• Micropillar compression
• Crystal plasticity finite element
• Inverse identification
• Identifiability analysis