[SY-E10] Understanding nanocontact plasticity through massive MD simulations
This presentation concerns comprehensive molecular dynamics (MD) simulations of nanocontact plasticity in body-centered cubic (BCC) and face-centered cubic (FCC) crystals. The main focus is on the understanding of the evolution of the nanoscale material hardness with increasing tip penetration through detailed analyses of the distinct defect nucleation processes which result in the formation of a permanent imprint. It is shown that the gradual development of an entangled defect structure essentially governs the evolution of material pileup at the contact boundary, a feature that explains the different FCC and BCC imprint morphologies and topographies that develop depending on loading orientation. The present analyses provide a fundamental background to understand why BCC surfaces are harder than FCC surfaces at the nanoscale, including the role of the elastic response of the indented crystals. Novel MD simulations for crystals containing a preexisting (dense) dislocation network further confirm the pivotal role of the incepted defects upon indenter tip penetration. Our analyses contribute to the understanding of indentation size effects in submicrometer-sized material volumes, where a physical rationale to the validity of strain gradient plasticity and geometrically necessary dislocations is essentially lacking. Finally, our investigation leads to the finding of a general correlation between the nanohardness and the yield strength measured at the nanoscale under uniaxial loading conditions.