Grain-scale experimental validation of crystal plasticity finite element simulations of tantalum oligocrystals

Abstract

In this work, the grain-scale elastoplastic deformation behavior of coarse-grained body centered cubic (BCC) tantalum was simulated using a crystal plasticity finite element method (CP-FEM) and compared to experimental measurements of intragranular strain and rotation fields. To mitigate the effects of unknown subsurface microstructure, tantalum tensile specimens with millimeter-sized grains provided nearly constant microstructure through the thickness of the tensile bar. Experimental validation was performed in three ways: (1) electron backscatter diffraction (EBSD) to map intragranular rotation, (2) high-resolution digital image correlation (HR-DIC) to map the surface strain field, and (3) surface profilometry to map the out-of-plane topographic distortion. To ensure a direct apples-to-apples comparison to experiments, the details of the initial microstructure and boundary conditions were carefully replicated in the model. The deformation predictions using this novel BCC CP-FEM model for tantalum agree reasonably well with the experimental measurements. In addition, the model successfully predicted the failure location of a specimen subjected to large plastic strains. Several model parameters were explored that influence the BCC CP-FEM predictions such as the mesh dependence, the choice of active slip planes in BCC metals and the assignment of initial crystal orientations.