Nanoindentation Modeling of Viscoplastic Solids
Authors:Ee Jane Lim, Nisha Mohan
Mentor:Julia Greer, Assistant Professor of Materials Science and Mechanics, California Institute of Technology
We consider an isotropic, three-dimensional continuum mechanics-based model to describe the dynamic, finite deformation of elastic-viscoplastic solids in response to quasi-static nanoindentation loading, a continuation of the analysis of the two-dimensional uniaxial compression model recently developed and understood in Hutchens et. al. (2011). This indentation model is based on a compressible elastic-viscoplastic constitutive relation with piecewise, linear hardening-softening-hardening flow strength. The model demonstrates the formation of a stress-concentrated region in the vicinity of indented region i.e. the plastic zone which propagates with increasing strain. We explore the effects of varying hardening-softening-hardening flow strength parameters, mesh size and density gradient on the radius and depth of the plastic zone propagation in the material. Unlike in monolithic materials as shown in Ahn and Kwon (2012), we observe linearly increasing radius and depth of the plastic zone with increasing strains for one case of softening-hardening transition flow strength function, which conforms to non-linearity for a different function and hence explain the differences.