A numerical investigation of slip evolution of shear crack faces oriented arbitrarily under non-steady contact

Shear loading is induced on the surfaces of a crack that is aligned at an arbitrary angle in relation to the direction of compressive loading. Contact faces may experience relative slip if the tangential stress along the crack surpasses the friction threshold determined by the product of normal stress and coefficient of friction. In contrast, other regions remain in stick contact with a lower level of shear stress than the friction limit. The resulting slip motion generates additional stress, potentially driving already slipped points further. The overall motion of crack faces is constrained by the bonding tip. Therefore, the stick-slip conditions can not possibly be determined in advance, and the slip evolution should thus be investigated for the analysis of friction fracture, especially in cases of non-steady contact, such as rolling or loading-unloading contact. This study explores the loading history effect on stick-slip contact of arbitrarily oriented shear cracks. The crack is assumed as distributed glide dislocations based on the discrete dislocation technique. The loading is incrementally applied until the targeted amplitude with the slip displacement gradually accumulating during the contact cycle. The initial contact position is successively changed during a rolling contact process, while the loading amplitude is decreased when followed by an unloading process. The factors that influence the stick-slip patterns of crack faces, including loading history, crack orientation and coefficient of friction, are investigated. The developed methods are expected to provide insight into the study of contact mechanics, and the conclusions can be used to predict the frictional fracture under rolling or loading-unloading contact.