Atomistic simulations of elastic deformation and dislocation nucleation in Al under indentation-induced stress distribution

Preliminary simulations of simple shear deformation and indentation simulations using different radii of a spherical indenter are performed using molecular dynamics in order to uncover the internal stress state for elastic deformation and subsequent initial plasticity under nano-indentation. An atomic single-crystalline aluminium model containing up to 1,372,000 atoms and an ideal friction-free spherical indenter are presented in a set of simulations. Effects of the stress distribution using several kinds of spherical radii of indenters on the critical condition of dislocation emissions are discussed with much emphasis. The critical shear stress for the dislocation emission under indentation is well accorded with the shear strength under the simple shear deformation exposed to the equivalent external stresses to the indentation-induced stress states. It is confirmed that shear strength strongly depends on the external stress component and therefore, high compressive stress states generated beneath the indenter lead to the much higher critical shear stress than μ/2π.