The effect of single crystal elastic and plastic anisotropy on stress and strain heterogeneity: comparison of olivine to other common minerals

In order to investigate the influence of single crystal elastic anisotropy on the heterogeneity of stress distributions during polycrystalline deformation multiple deformed crystalline materials were analyzed using electron backscatter diffraction (EBSD). Deformation experiments were conducted on samples of Solnhofen limestone using a modified Griggs piston cylinder apparatus at UNLV, and also on San Carlos olivine using the D-DIA multi-anvil press at the National Synchrotron Light Source beamline X17B2. Analysis of the mechanical twins in deformed calcite and kink bands in olivine help elucidate deviations in local stress directions away from that of the applied macroscopic stress. Combined calculated compression directions in each microstructured grain shows that in both olivine and calcite the mean deviation of local stresses is approximately 25°, with maximum being 35° and 40° respectively. Experimental observations were compared with finite element models (FEMs) of olivine, quartz and calcite. The models were constructed using the full elastic tensor of each material, as well as an estimated single crystal yield stress. The FEMs show that with increasing single crystal elastic anisotropy there is an increase in deviation of the local compression direction away from the macroscopic compression direction, up to 12, 13 and 19° respectively, but lack the magnitude that is observed in the experimental deformation. I hypothesize that this discrepancy originates from the lack of a grain boundary structural component in the FEMs, thus providing evidence of the importance of grain boundary sliding during polycrystalline deformation. In addition, the experimental deformation results do not show a strong correlation between the elastic anisotropy of the single crystal and the spread in local compression directions. This behavior is attributed to the differing plastic anisotropy of both materials, indicating the importance of plastic anisotropy in the prediction of stress and strain heterogeneity in polycrystalline deformation based off of single crystal properties.