[SY-L2] Symposium L-2

[SY-L2] Comparison of surface-indentation and pillar-compression at the nanoscale of FCC metals: Unification of size effects using 3D Discrete Dislocation Dynamics

^○Hengxu Song^1,2, Stefanos Papanikolaou^1,2 (1.west virginia university, United States of America, 2.johns hopkins university, United States of America)

Plasticity of FCC materials at the nanoscale is size dependent, abrupt and stochastic. These features have hindered the predictability of nanoscale plasticity and consequently, engineering at small scales. Surface indentation and pillar compression have been the two major pathways towards developing predictive theories. While surface indentation has strong relevance to engineering, the development of theories has been more efficient for pillar compression studies. In this work, we connect the flat-punch nanoindentation and uniaxial pillar compression size effects under one unified framework. Through three-dimensional Discrete Dislocation Dynamics (3D DDD) simulations, we investigate uniaxial compression of pillars and also flat-punch nanoindentation, for identical pre-existing dislocation densities. We study various pillar/punch sizes (0.25 - 8 μm) and experimentally relevant initial dislocation densities. We demonstrate that Tabor’s law, which is valid at the macroscale, also extends at the nanoscale, given that statistical averaging is appropriately considered. We develop the statistical theory behind this nanoscale “Tabor’s law” using probabilistic concepts and we confirm its validity using 3D-DDD simulations.