Crack propagation determined by energy release rate in cortical bone ultrasonic vibration assisted cutting

Abstract

In orthopaedic surgery, bone cutting may occur serious mechanical damage due to large crack propagation, which impedes patient postoperative recovery. Ultrasonic vibration assisted cutting (UVAC) has emerged as a leading technique in bone cutting owing to its remarkable advantages, including minimal damage and cutting force. However, how to diminish its damage during bone UVAC remains challenging. Hence, this study established a sophisticated model to calculate the energy release rate for cortical bone UVAC and predicted the critical cutting depths of modes II and I brittle crack propagation. This superiority stems from the synergistic effects of periodic tool separation and the acoustic softening effect inherent in UVAC, which contribute to a lower average energy release rate and a subsequently reduced cutting force. Nevertheless, the high instantaneous energy release rate during UVAC can exceed the material's critical threshold for crack propagation, leading to the initiation of microcracks and thereby inducing material embrittlement behaviour. These insights shed light on the material removal mechanism of bone UVAC in medical orthopaedic surgery, thus enriching our understanding and potentially guiding further advancements in this field.