Cracking behavior during scratching brittle materials with different-shaped indenters

Abstract

The cracking behavior greatly influences the material removal and surface integrity during the abrasive machining of brittle materials. The abrasive machining can be simplified as a series of scratching by different-shaped indenters. In this paper, a scratch-induced stress field model is built to analyze the cracking behavior during scratching brittle materials. The model considers conical, pyramidal, and spherical (CPS) indenters and correlates the scratch-induced principal stress with workpiece material properties, indenter geometries, and scratch behavior parameters (e.g., scratch normal load, tangential load, friction coefficient, scratch depth). With the model, the effects of scratch depth and indenter geometries on the scratch behavior and cracking behavior are investigated. The results show that the scratch load decreases when a sharper indenter or a spherical indenter with a smaller radius is used. The larger the scratch depth, the easier it is for radial, median, and lateral (RML) cracks to initiate. There is an optimal indenter half-apex angle at which it is most difficult to initiate radial and median cracks. The lateral crack easily initiates when the indenter becomes sharp. The initiation position of radial crack changes from being in front of the indenter to being behind it as the scratch depth increases or the half-apex angle decreases. The propagation angle of radial crack decreases, while that of median crack increases with an increase in scratch depth. The sizes of RML cracks increase with an increasing scratch depth or half-apex angle. Finally, the model is validated through scratching experiments on fused silica using CPS indenters and by referencing previous research. It demonstrates that the model can accurately determine the sizes of RML cracks, with an average relative error of less than 11%. This research provides guidance on selecting suitable process parameters or indenter geometries to increase the material removal rate and mitigate the crack damage during the abrasive machining of brittle materials.