Investigation on the surface formation mechanism in scratching of CFRP composites with different fiber orientations

Rotary ultrasonic machining (RUM) is an effective approach to process carbon fiber reinforced polymer (CFRP) composites. However, the surface formation mechanisms in RUM for different fiber orientations have not been comprehensively investigated. In this research, ultrasonic vibration-assisted scratching (UVAS) and conventional scratching (CS) tests with invariant cutting depth were conducted innovatively to expose the material removal mechanism. Based on the kinematics analysis, the characteristics of material removal process have been compared between UVAS and CS, and dynamic changes of actual cutting angle with the addition of ultrasonic vibration have been studied for the first time. The groove morphologies and scratching loads were analyzed for different fiber orientations and scratching parameters. The experimental results revealed that the fracture mode of fiber was principally decided by cutting angle. And the surface crack propagation can be significantly inhibited in UVAS due to the intermittent cutting behavior, increase of instantaneous velocity and the dynamic alteration of direction and magnitude of actual cutting angles. This research will help enable an in-depth understanding of the material removal mechanism of CFRP composites in RUM, and is beneficial for the optimum utilization of vibration assisted processing for advanced composites.