Subsurface Damage Model in Single and Double Scratching of Fused Silica with a Blunt Indenter

The subsurface damages (SSDs) generated during abrasive processes greatly impact the service performance and life of the devices or components made from brittle materials. The abrasive processes can be simplified as multiscratching where the abrasive grits tend to be blunt. Consequently, the evaluation of SSDs in the scratching with a blunt indenter is worth of study. In this paper, by extending the blunt indenter-related indentation fracture mechanics and deriving the analytic equations for the contact areas between the indenter and the workpiece, a theoretical SSD depth model is first developed for the single and double scratching of brittle materials. The model correlates the depth of subsurface cone, median, and lateral cracks with the indenter nose radius, scratching depth, residual depth, normal load, tangential load, scratch spacing, and workpiece material properties. To validate the model, scratching experiments are carried out on polished fused silica under different scratch spacing, and the effects of scratch spacing on the surface/subsurface morphologies of scratch grooves, scratching load, and friction coefficient are investigated experimentally. The results show that the radial, cone, median, and lateral cracks are coexistent in fused silica. The second scratching leads to an increase in the fracture degree of the first one, while the SSD depth in double scratching approximates that in single scratching. A small scratch spacing leads to an increase in tangential load or friction coefficient while a decrease in normal load. It is proven that the theoretical model can accurately determine the upper/lower bounds of scratching normal load and subsurface crack depth considering the workpiece fracture degree. Moreover, it is revealed that the SSD depth increases slightly with an increased friction coefficient. This research contributes to the evaluation of SSDs in the abrasive-processed fused silica or similar brittle materials.