Crystal plasticity finite element simulations of nanoindentation and simple compression for yielding of Ta crystals

Experiments and corresponding crystal plasticity finite element (CPFE) simulations of spherical nanoindentation were performed to determine yield stress under indentation of fifteen Ta single crystals randomly distributed in the orientation space. Agreement between the measured and simulated indentation yield stresses and initial hardening slopes demonstrated accuracy of the model. Moreover, simple compression simulations were performed for the same crystals to study the differences in compressive versus indentation yielding. Ratios of the indentation to compressive yield stress were found to vary with crystal orientation in the range from 2.6 to 3.6. The simulations allowed us to reveal underlying deformation mechanisms accommodating the yielding in indentation and simple compression. It is found that more crystallographic glid mechanisms activate under indentation than simple compression owing to the more complex state of stress and strain in indentation than in compression. Owing to the activation of more glide systems in indentation than in simple compression, the indentation yield stress is less anisotropic than the simple compression yield stress. The modeling framework, simulation setups, results, and insights from the results are presented and discussed in this paper.