Elastic instabilities in single crystal thin film during nano-indentation loading
Akanksha Garg (CMU), Craig Maloney (Carnegie Mellon University)
Instability in Solids and Structures
Tue 10:45 - 12:15
Barus-Holley 190
We perform atomistic computer simulations of a two-dimensional perfect hexagonal crystal subjected to nano-indentation loading.For most crystallographic orientations and interatomic interactions, we find agreement with previous results for the case where the nearest-neighbor direction was perpendicular to the loading axis (cond-mat/1205.1700). In these orientations, the critical modes are localized sharply along a single line, like the nucleation of a dislocation dipole. The embryo size, $\psi$ scales with the thickness of the film, $L$, and radius of the nano-indenter, $R$, in a non-trivial way that is independent of crystallographic orientation and the interatomic potential. For these localized modes, we also perform mesoscale analysis where the meso-region is centered along the slip plane. When the meso-region is not centered at the core of instability,the presence of incipient instability can only be revealed up to a critical distance from the core that depends on the radius of the meso-region radius and the embryo size. For some crystallographic orientations with high surface energy, such as when the nearest-neighbor direction is co-incident with the loading axis, we find a new failure diffused mode that emerges for very flat indenters and competes with the dislocation-like mode. We perform homogeneous loading simulations to roughly estimate the critical axial strain at which the transition from the localized to delocalized mode occurs for different orientations.