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<div><p>Ultrasonic vibration technology has significant potential for breaking hard rocks. Understanding the optimal frequency for rock breaking under ultrasonic vibration can significantly reduce the cost of rock breaking and extend the service life of polycrystalline diamond compact (PDC) cutters. This is important for practical engineering applications. This study presents a three-dimensional finite element model of rock breaking by a PDC cutter under ultrasonic vibration. The model was established using ABAQUS software and used to simulate the dynamic rock breaking process of the PDC cutter. A comparative analysis was performed between conventional rock breaking and rock breaking under ultrasonic vibration. According to the result, ultrasonic vibratory rock breaking is more likely to cause damage to the rock when a PDC cutter is used, particularly at a vibration frequency of 40 kHz. As the ultrasonic vibration frequency (20–40kHz) increases, the mechanical specific energy (MSE) initially decreases and then increases. The MSE reaches a minimum value at a frequency of 20–25 kHz, representing a decrease of 15.52%–22.24% compared with conventional rock breaking, which can significantly improve the rock breaking efficiency and reduce the drilling cost. The temperature of the PDC cutter increases significantly under ultrasonic vibration compared with conventional rock breaking. Additionally, the temperature of the PDC cutter increases gradually with an increase in the vibration frequency. These results provide theoretical support for the use of ultrasonic vibration technology.</p></div>