Hardness and friction coefficient of fused silica under scratching considering elastic recovery

Elastic recovery of fused silica under scratching has significant effects on its hardness and friction coefficient. However, the effects are seldom considered in previous calculation models causing misestimation of hardness. In this work, scratching on fused silica with a conical indenter and a Berkovich indenter was investigated by finite element analysis (FEA). Meanwhile, analytical models of apparent friction coefficient were built by modeling the geometry of contact regions as a sector and a triangle for the conical and Berkovich indenters, respectively. With the effects of elastic recovery taken into account, the apparent friction coefficient predicted by these analytical models is consistent with FEA. The results provide a reference for calculating hardness of materials with large E/H (Young's modulus/hardness) like fused silica during scratching, which consider elastic recovery. Besides, by analogues to indentation strain, a new parameter, i.e., sliding strain epsilon(s), is proposed. FEA reveals that epsilon(s), can be used to characterize the effects of indenter geometry and sliding direction on scratching. As demonstrated by the results, the apparent friction coefficient and hardness increase with epsilon(s,) while the elastic recovery ratio decreases with epsilon(s).