Strain-gradient crystal plasticity model with slip-system level GND tracking: Simulation vs experiment for sequential strain path change in AA6016-T4

Abstract

Crystal plasticity models that track strain gradients and associated geometrically necessary dislocations (GNDs) typically determine the Nye tensor, mimicking the experimental approach. However, estimating GND densities for each slip-system is then intrinsically ambiguous. This study seeks to build upon current state of the art by quantifying GNDs at the slip-system level in the model using the local strain gradients. The model is exercised by replicating experiments undertaken on AA6016, which are performed under multi-step strain paths; both GND and SSD populations are quantified at various stages using both high resolution EBSD (HREBSD) and XRD. A full 3D volume of the material is extracted using ion beam serial sectioning to enable the creation of a high-fidelity model of the material.

The combined modeling and experimental campaigns conclude that: 1) Calculation of the GND content at the slip level gives effectively equivalent GND evolution as the tradition Nye tensor method, but provides the significant advantage of knowing unambiguously the contribution on each slip system. 2) The net hardening predicted by the SGCP model is accurate, including prediction of a rapid increase in hardening (and associated dislocation content) following strain path change; and 3) Comparisons of observed and simulated GND populations reveal that buildup in the real sample is dominated by precipitate distribution rather than by grain boundary (GB) networks; such precipitates are not present in the current model, hence this result was not predicted.