Nanoscale contact behavior of α-quartz asperities — A molecular dynamics approach

Rock surfaces are composed of asperities at various scales. Accurate modeling of the multiscale contact deformation of asperities is of great importance to study the earthquake source mechanics and hydraulic properties of fractures. In this study, to shed light on the nanoscale contact behavior of rock asperities that might not have been paid much attention to in previous studies, we simulated a series of nanoscale contact processes of α-quartz asperities under single-asperity contact employing molecular dynamics method. In addition to the investigation of the influence of contact configuration and asperity size on the asperity failure, we compared the simulation results with macroscopically elastic and elastoplastic contact models to evaluate the multiscale applicability. We observed that fracture occurs in the nanoscale α-quartz asperities during contact process, inconsistent with the traditional assumptions of elastic and elastoplastic deformation of rock asperities. Moreover, the asperity size and contact configuration significantly affect the failure mechanism of α-quartz asperities, specifically the transition from plasticity-dominant failure to fracture damage. Finally, a multiscale disparity exists, where macroscopic contact models are limited to predict the nanoscale contact behavior of α-quartz asperities. The results obtained here underscore the need to re-evaluate the assumptions of rock asperity deformation and emphasize the importance of considering contact configurations and multiscale effects of rock asperities.