[P1-17] Nanoindentation of Nanoparticles -A Molecular Dynamics and Discrete Dislocation Dynamics Simulations Study
When decreasing the size of metallic specimens into the sub-micrometer scale, they can drastically change their mechanical properties. While plasticity at this scale is commonly studied using compression tests, nanoindentation can reveal the importance of free surfaces on the depletion of dislocations during the deformation. In this talk, we present a computational study on how the size and shape of defect-free nanoparticles affect the mechanical response to nanoindentation. Using Molecular Dynamics (MD) simulations and Discrete Dislocation Dynamic (DDD) simulations, we simulate nanoindentation of Au faceted nanoparticles in a height range of 9-150 nm. The DDD simulations are coupled with a finite element analysis, in order to reproduce the stress field generated during nanoindentation. Since the nanoparticles are initially pristine (dislocation free), a nucleation criterion for dislocations is introduced in the DDD simulations. When indenting along a <111> direction, the simulations show that shear dislocation loops are nucleated beneath the indent on all {111} slip planes. Those shear dislocation loops interact and form v- and u-shaped dislocations or prismatic loops that glide towards the lower part of the nanoparticles, facilitating their escape from beneath the indent. Two other mechanisms are shown to control the escape of dislocations laterally from the upper part of the nanoparticle. In one, segments of shear dislocation loops, that are nucleated on the {111} slip plane parallel to the upper surface of the nanoparticle, cross-slip and escape from the upper surface, forming two half prismatic loops that glides parallel to the upper facet. In another mechanism, dislocations on two different slip planes interact and form a glissile dislocation segment that glides lateraly and escapes the nanoparticles. The effect of size on the various dislocation mechanisms is discussed.