Non-synchronous ductile and brittle removal mechanisms for conventional and ultrasonic vibration-assisted scratching of ceramic matrix composites

Ceramic matrix composites (CMCs) are widely recognised as difficult-to-machine materials. The use of diamond abrasive tools combined with ultrasonic vibration offers unique benefits for precision machining. Understanding the differences in material removal mechanisms between ultrasonic vibration-assisted scratching (UAS) and conventional scratching (CS) is crucial for achieving efficient, accurate machining of high-value workpieces. Herein, variable-depth CS and UAS tests were performed, revealing for the first time two brittle removal mechanisms in CMCs: fibre-bending fracture from non-synchronous removal in CS and cyclic indentationhammering-crack extension in UAS. Further, the non-impulse (CS) and impulse (UAS) force models are established for ductile and brittle removal, respectively. These models were successfully validated through experimental scratching-force data. Results suggest that material removal behavior is primarily influenced by the type of fiber bending fracture and crack extension tip shielding.