Universal scaling laws for homogeneous dislocation nucleation during nano-indentation. (October 2016)

• Record Type: Journal Article
• Authors: Garg, Akanksha; Maloney, Craig E.
• Is Part Of: Journal of the mechanics and physics of solids. Volume 95(2016:Oct.)
• Page Start: 742
• Page End: 754
• Publication Date: 2016-10
• Subjects: Mechanics, Applied -- Periodicals; Solids -- Periodicals; Mechanics -- Periodicals; Mécanique appliquée -- Périodiques; Solides -- Périodiques; Mechanics, Applied; Solids; Periodicals; 531.05
• DOI: 10.1016/j.jmps.2016.04.026
• Languages: English
• ISSNs: 0022-5096

Abstract

Abstract: We perform atomistic simulations to study the mechanism of homogeneous dislocation nucleation in two dimensional (2D) hexagonal crystals during nanoindentation with a circular indenter of radius R . We study both a realistic embedded atom method (EAM) potential for Al in addition to simple pair-wise potentials: Lennard-Jones, Morse, and Hookean springs. The nucleation process is governed by the vanishing of the energy associated with a single energy eigenmode. The critical eigenmode, or dislocation embryo, is found to be localized along a line (or plane in 3D) of atoms with a lateral extent, ξ, at some depth, Y ⁎, below the surface. For all interatomic potentials, the scaled critical load, F c / R, and scaled critical contact length, C c / R, decrease to R -independent values in the limit of large R . However, ξ / R and Y ⁎ / R display non-trivial scaling with R despite the R independence of F c / R and C c / R . We show that although both the interaction potential and the orientation of the lattice affect the prefactors in the scaling relations, all the scaling laws are robust. Furthermore, we show that a stability criterion proposed by Van Vliet et al. based on the minimum eigenvalue, Λ, of the local acoustic tensor predicts the location, orientation, and polarization of the dislocation embryo with a high degree of accuracy for all potentials and crystallographic orientations. However, we also show that, for all crystallographic orientations and interaction potentials, Λ erroneously indicates instability before the true instability occurs.