Strain heterogeneity in deformed Carrara marble using a microscale strain mapping technique

Abstract

Using high‐resolution surface imaging and a split‐cylinder technique, we mapped the strain heterogeneity in Carrara marble samples deformed to bulk strains <25%, under conventional triaxial loading, at 400–700°C, 300 MPa confining pressure, and strain rates of 10−4 to 10−5 s−1. To map strain, we deposited grid markers on the polished surface of a half cylinder, performed mechanical tests on composites of two half cylinders, compared the positions of each marker in undeformed and deformed samples, and computed the spatial distribution of strain. Strains over the scale of a few microns varied by as much as 300%. Localized deformation occurred along twins and grain boundaries but was also present as patches in intragranular regions. The heterogeneity is more pronounced at scales smaller than grains, but the strain averaged over individual grains also varied by 50%. After deformation, the crystallographic orientation of individual grains relative to the compression direction was measured by electron backscattered diffraction. Inverse pole figures of the aggregate lattice‐preferred orientation (LPO) have a maximum near e(018) and are consistent with previous studies. The observed LPO is qualitatively consistent with that produced by simulations using a simple viscoplastic self‐consistent (VPSC) code that did not include mechanisms other than slip or twinning. The qualitative comparison of observed and simulated LPO was not sensitive to the model for the crystallographic resolved shear stresses for slip. However, the VPSC simulation was ineffective in predicting individual grain rotations.