Sliding and nano-fretting discrete dislocation plasticity analyses are carried out to investigate the damage of material between a rigid sinusoidal-shaped asperity and a single crystal film. Both sets of calculations are conducted using a model that describes the contact as a cohesive zone, which is used to provide a relationship between the shear traction and the relative displacement within the contact. Results of sliding simulations reveal the dependence of the shear stress and friction coefficient on the contact size. There are three regimes of shear stress response, which are dominated by the cohesive relation, contact size and macroscopic plasticity, respectively. Fretting simulations that were carried out using a 20nm stroke length on a single crystal aluminum film predict a size dependence of the cyclic shear stress upon the contact size: friction is dominated by adhesion at small contact areas while it is governed by plasticity at large contact sizes.
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