Nucleation location and propagation direction of radial and median cracks for brittle material in scratching

Abstract At present, diamond wire sawing technology is a mainstream method for wafering brittle materials such as silicon crystal, SiC crystal, sapphire, ceramics, optical glass and so on. Microcracks will occur on the wafers surface inevitably during sawing owing to the high brittleness and hardness of brittle material. The existence of microcracks and their size, orientation and distribution not only affect the surface quality and fracture strength of wafers, but also have an important impact on the subsequent processing effect of wafers after sawing. Therefore, the further investigation on the formation and propagation direction of microcracks is needed during diamond wire sawing. In this paper, an analytical model of the elastic stress field for brittle material is established during single abrasive scratching. The stress fields in front of and behind the indenter are analyzed respectively. Two different material removal modes, ductile removal and brittle removal, are considered. To evaluate the two different material removal modes, influence factor μ is proposed. The nucleation location and propagation direction of radial crack and median crack of several materials are predicted by analytical model. The result show that the radial crack nucleates behind the indenter. The deflection angle between propagation direction and scratching direction is about 35–60°, and its size depend on the material removal modes. The nucleation location of median crack is no longer at the bottom of the plastic zone, but will deflect toward the scratching direction during scratching. The size of deflection angle depends on the tip half angle of indenter. When the tip half angle is 55–80°, the deflection angle decreases with the increase of the indenter half angle. All predicted results are in good agreement with the experimental data of relevant scholars. At the end, the half-penny crack (radial/median crack system) presented in indentation process is extended to scratching process.