Micromechanical‐based experimental and analytical studies on rate effects and stick‐slip instability of smooth quartz surfaces in the presence of plastic and non‐plastic gouges

Abstract We examined with micromechanical‐based experiments the influence of shearing rate on the tangential contact behavior of smooth (very low surface roughness) flat quartz surfaces with montmorillonite and crushed aggregates as gouges. On decreasing the shearing rate by one order of magnitude, significant changes in the stick‐slip instability were observed; increase in force‐drop, recurrence interval and slip velocity. The initial tangential stiffness increased on decreasing the shearing rate. The type of gouge particles also influenced the behavior of the interfaces; for example, higher friction and stable sliding were observed for angular particles (non‐plastic gouge) compared to flaky particles (plastic gouge). The partition of the tangential force‐displacement relationship based on the shape of the curve was also dependent on the shearing rate. On a qualitative standpoint, the results presented in this micromechanical‐based study were in agreement with macro‐scale test results published in the literature, although different scale tests were also performed in the present work, from grain‐level to direct shear test size. The changes in the behavior of stick and slip components of the tangential force and the contact area with shearing rate were analytically studied, and the corresponding variations in the normal load‐displacement relationship were also discussed. This experimental micromechanical‐based study with additional analytical support, provides a preliminary understanding of the frictional behavior of different gouges under shearing rates of one folder difference and also provides insights into the stick‐slip instability behavior at a microscopic (grain‐scale) standpoint.