[S08] PM-2

[S08-29] Molecular Dynamics Investigation on the Lifetime of an α-Quartz Gouge Particle Under Shearing a Pair of Asperity Walls

*SHENG LI¹, Eiichi Fukuyama¹ (1. Kyoto University, Department of Civil and Earth Resources Engineering, Graduate School of Engineering, Kyoto, Japan)

The mechanical behavior of gouge particle could closely relate to the friction properties of rocks, which may influence the nucleation, rupture propagation and termination of earthquakes. In this study, by using molecular dynamics, we explicitly simulated a series of 3D dynamic friction processes of a single spherical α-quartz particle with rough surfaces composed of semi-spherical asperities. We investigated the effects of the normal force, particle size, asperity interval and contact configurations on the dynamic failure of a particle during shearing. Our model initially involves asperities that are aligned with the same asperity interval along the sliding direction and meanwhile all replicated in the direction perpendicular to the sliding with the same asperity interval. Afterwards, two initial contact conditions are considered: the particle center is aligned with the geometric centers either formed by two upper and two lower asperities in the x directions (Case I) or formed by four upper and four lower asperities in two rows (Case II). Finally, we changed the normal load (allowing the fracture to occur), particle size (either 5R or 6R, where R = 3.4 nm) and asperity interval (either 0.5 R or R in sliding direction) for the two contact cases to investigate the particle failure. The loading velocity was set at 30 m/s and asperity radius at 4R. Our results show that under all simulations, the normal load significantly affects the particle lifetime. Under the high normal load, the particle breaks within a short sliding distance during the stick stage with asperities. In contrast, under the low normal load, the particle undergoes a long-distance adhesive wear (plastic flow) and shrinkage of the particle volume. It breaks when the volume reduces to a critical size. This process, from adhesive wear to fracture, persists with the increased particle size, where the larger particle experiences a longer adhesive wear distance. Furthermore, the asperity interval generally increases the particle lifetime in our model setup. Contact configurations also have effects, where the particle in Case I cracks more easily over short distances, while in Case II it endures longer plastic wear before breaking under the same normal load. Finally, an interesting finding is that the lifetime of particle could be related to the wear-induced shape.