Discrete element method to study the subsurface crack propagation trend during vertical ultrasonic vibratory cutting of sapphire

The introduction of ultrasonic vibration had a significant effect on the expansion tendency of sub-surface microcracks, but the reason for influencing the expansion tendency of microcracks is not clear. In this study, the vertical ultrasonic vibration cutting process of sapphire was simulated by the discrete element method, and the reasons for the expansion of sub-surface microcracks during the cutting process were revealed from the viewpoint of cutting force and stress. The results of the study show that the sub-surface microcracks in the cutting process are mainly caused by tensile stresses, and the tensile stresses increase with the increase of amplitude and frequency; as the amplitude and frequency increase, the degree of cutting force fluctuation, the depth of the sub-surface cracks, and the number of cracks increase more drastically; the tensile stress at smaller amplitudes is smaller than in normal cutting, and the location of the maximum tensile stress is closer to the machined surface, which inhibits the expansion of the sub-surface cracks. Finally, the vertical ultrasonic vibratory cutting and normal cutting sapphire experiments were comparatively studied, and the experimental results were in agreement with the simulation results. This research provides theoretical guidance for the realization of low damage and efficient processing of sapphire materials.