Modeling and Characterization of Grain Scale Strain Distribution in Polycrystalline Tantalum

A common sample geometry used to study shear localization is the "tophat" an axi-symmetric sample with an upper "hat" portion and a lower "brim" portion The gage section lies between the hat and brim The gage section length is on the order of 0 9 mm with deformation imposed through a Split-Hopkinson Pressure Bar system at maximum top-to-bottom velocity in the range of 10-25 m/sec Detailed metallographic analysis has been performed on sections of the samples to quantify the topology and deformation state of the material after large deformation shear These experiments performed with polycrystalline tantalum have been modeled using a multi-scale polycrystal plasticity approach A Voronoi tessellation based microstructural model and a coupled thermo-mechanical elasto-viscoplastic crystal plasticity model was used The crystal plasticity model allowed for slip to occur on the twelve {110} < 111 > and twelve {112}< 111 > slip systems Three numerical models were produced using three different realizations of initial crystallographic texture distribution within the same morphological microstructure and the results presented The detailed metallographic analysis of the deformed sample shear zone produced an estimate for the strain profile within that region and these results are compared directly to the three numerical simulation results Although the models predict a stress response which is greater than that observed experimentally, the local strain response compares very well with the results of the metallographic analysis