On spherical nanoindentations, kinking nonlinear elasticity of mica single crystals and their geological implications

In this paper, we show, using cyclic spherical nanoindentation experiments, that the deformation mechanisms in mica, including basal plane ruptures and delaminations, can be explained by invoking the presence of mobile dislocation walls, and incipient and regular kink bands. Our results clearly show that the energy dissipated or that was stored during the deformation of muscovite depends critically on its previous deformation history and/or the pre-existing defect concentration. Once nucleated, the dislocation-based incipient kink bands are believed to be responsible for the nonlinear elastic deformation and hysteretic loops obtained during cyclic loading. Moreover, a model is presented to estimate the number and distribution of dislocations and the energy consumed in their motion under the indenter. From the model, we also estimate the critical resolved shear stress for the motion of basal plane dislocations under the indenter. The implications of this work can be extended beyond mica to understand the nonlinear hysteretic deformation in other geological formations dominated by layered minerals.