On crack suppression mechanisms of ultrasonic elliptical vibration cutting of 3Y-TZP ceramics

Ultrasonic elliptical vibration cutting (UEVC) is a promising technique to realize the crack-free machining of ceramic materials. However, the underlying crack suppression mechanism and its impact on the ductile-brittle transition (DBT) behavior of ceramics still remain poorly understood. In the current work, the material removal characteristics of 3Y-TZP ceramics under UEVC, including the crack propagation process, stress dis-tribution condition, and critical transition depth, were rigorously studied by using both the smoothed particle hydrodynamics (SPH) simulation and the experimental method. It was found that the material removal behavior and critical transition depth were highly related to the ultrasonic speed ratio (Rs) that defines the ratio of the nominal cutting speed to the maximum ultrasonic velocity along the cutting direction. A critical (Rs) value of 0.128 was determined by the analytical method, beyond which the crack suppression mechanism of UEVC is mainly due to the time-varying cutting speed and angle. When the Rs is lower than the critical value, the reduction of the effective cutting thickness caused by the overlapping trajectory becomes a dominant factor in enlarging the ductile regime and in improving the machining quality of 3Y-TZP ceramics.