Molecular dynamics simulation of single and repeated indentation

Atomic-scale material responses of dynamic metal-like substrates due to single and repeated indentation by metal-like or covalent rigid tips are interpreted in light of three-dimensional molecular dynamics simulation results. Single-indentation results for a face-centered-cubic metal substrate indented by a relatively blunt tip of the same material and a sharper pyramidal tip of a covalent material are compared to elucidate the effects of interfacial atomic potential and tip shape on the deformation behavior. Force hysteresis occurs due to inelastic deformation and heating of the substrate. The abrupt decrease of the repulsive force during penetration is attributed to permanent deformation. The formation of a connective neck during unloading observed only in the indentations involving the metal tip is associated with the stronger interatomic forces and larger tip surface area in these simulations. The rapid decrease of the attractive force during retraction of the tip is associated with the reconstruction of the elongated neck. Results for different metallic substrates repeatedly indented by a rigid covalent tip up to a fixed maximum depth or maximum normal force are presented in order to reveal the evolution of deformation and heating in the substrate with indentation cycles. Repeated indentation gives rise to behaviors resembling cyclic hardening and softening observed at the macroscale. (C) 1997 American Institute of Physics.