Adhesion-induced instabilities in elastic and elastic-plastic contacts during single and repetitive normal loading

Adhesive interaction in spherical contacts was modeled with the Lennard-Jones (L-J) potential. Elastic adhesive contact was analyzed by the equivalent system of a rigid sphere with reduced radius of curvature and a half-space of effective elastic modulus. The critical gap at the instant of abrupt surface contact (jump-in) and separation (jump-out) was determined from the deformed surface profile of the elastic half-space and geometrical relationships. A finite element model of a rigid sphere and an elastic-plastic half-space was used to examine elastic-plastic adhesive contact. Surface adhesion was modeled by nonlinear springs with a force-displacement relationship governed by the L-J potential. The evolution of the interfacial force and the central gap distance as well as the occurrence of jump-in and jump-out instabilities were investigated in terms of the Tabor parameter, plasticity parameter, and dimensionless maximum normal displacement. The force-displacement response due to several approach-retraction cycles was interpreted in the context of elastic and plastic shakedown behaviors using dimensionless parameters.