Collective Dislocation Behavior in Single Crystalline Aluminum Under Indentation

Abstract

Recent mesoscale experiments resulting in scale-dependency on the mechanical deformation have yielded the strain-gradient plasticity [1] and furthermore motivated the linkage between the discrete defects dynamics methodology and the continuous plasticity studies [2]. Especially, nanoindentation has been recognized as the most appropriate material testing to quantify the characteristic length [3]. Taking advantage of the controllable µN-level indent load and the nanometer-level displacement resolution, it can accurately monitor the mechanical response of the extremely localized stress and strain field. The reason of increase of microhardness observed in the ductile materials has been thought to be due to collective dislocation behavior extending under the indentation [4]. In fact, the density of the geometrically-necessary dislocation (GN dislocation) emitted from the surface is related to the strain gradient by compatibility requirements [5] and one can easily imagine the high density region of dislocation just beneath the indentation [6]. However, no one still refers the physical process of how the aggregate of dislocations dynamically evolves under the nonuniform stress distribution and leads to the scale-dependent hardening mechanism which may, in principle, be based on the mobility of the dislocations.