Friction and wear are two main tribological behaviors that are quite different for contact surfaces of distinct properties. Conventional studies generally focus on a specific material (e.g., copper or iron) such that the tribological result is not applicable to the other contact systems. In this paper, using a group of virtual materials characterized by coarse-grained potentials, we studied the effect of interfacial adhesion and material plasticity on friction and wear by scratching a rigid tip over an atomic smooth surface. Due to the combined effects of adhesion and plasticity on the nanoscratch process, the following findings are revealed: (1) For shallow contact where interfacial adhesion dominates friction, both friction coefficient and wear rate increase as the adhesion increases to a critical value. For deep contact where plasticity prevails, the variation of friction coefficient and wear rate is limited as the adhesion varies. (2) For weak and strong interfacial adhesions, the friction coefficient exhibits different dependence on the scratch depth, whereas the wear rate becomes higher as the scratch depth increases. (3) As the material hardness increases, both the friction coefficient and wear rate decrease in shallow and deep contacts.

The mechanical response of geomaterials to extreme dynamic conditions is essential to understanding planetary impacts, other geological and seismic events, and underground explosions. In this study, we present a multimechanism constitutive model to describe the dynamic response of polycrystalline quartz (e.g., nonporous quartzite), and implement it using a large scale computational analysis to simulate impact events. The active deformation mechanisms within quartz under dynamic loading consist of amorphization, fracture and granular flow. All of these mechanisms are integrated within the model in terms of their competition, evolution, and interaction during a complex loading history. A generalized amorphization model is introduced within a thermodynamically consistent framework on the basis of earlier work in Zeng et al. (2019a, https://doi.org/10.1016/j.jmps.2019.06.012), and accounts for the kinematics of finite deformation inside amorphization bands and the distinct physical properties of the amorphous phase. Fracture in the form of microcracking emanating from internal defects is also considered. Once the material is fully fragmented, the behavior transitions to granular flow. After determining the model parameters for polycrystalline quartz, we illustrate the model response using a representative volume element, where the competition of mechanisms is revealed under several typical loadings. Plate impact experiments and dynamic compression on a polycrystalline quartz foil are then simulated. The simulation results are compared with experiments to prove the predictive capability of the model in capturing the key features of quartz during impact events.