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.

Based on molecular dynamics, the effects of void and initial dislocation structure on incipient plasticity are investigated with single crystal copper samples. By introducing a void of different sizes and shapes and dislocations of different initial structures around the void in copper single crystals, we explore their effects on yielding as well as the dominated deformation mechanism. The main findings from this study are as follows: (1) for the samples with a void of the same size, the yield stress approaches to a specific value as the initial dislocation density increases; (2) for samples with a void of varying size, the yield stress becomes independent of the void size as it reaches a certain level, due to the saturation of preexisting dislocations around the void; and (3) as the strain rate increases, the effects of voids and preexisting dislocations on the yield stress become limited due to the response inertia, for which the phase transition from face-centered cubic to an amorphous phase occurs at an extremely high strain rate.

Frictional heating in cyclotrimethylene trinitramine (RDX) can generate hotspots, which are local regions of elevated temperature that may trigger explosion. In this study, we quantified the characteristic size of the hotspot to be approximately 20 Å based on the width of the nanoscale shear band in shock loading simulations and further examined the temperature rise in RDX crystals during high-speed nanoscratching using molecular dynamics simulations. These simulations were performed under varying sliding velocities, normal loads, and sliding directions to explore the relationship between friction coefficient, shear stress, and localized hotspots. Our results revealed that, despite the anisotropic friction properties, the temperature rise exhibited a consistent dependence on shear stress, with a critical shear stress identified above which the hotspots experienced a sharp increase in the temperature. This temperature transition correlates with localized melting, as demonstrated by the analysis of atomic temperature and bond-length changes. These findings enhance our understanding of the mechanical and thermal stability of energetic materials.