Numerical Investigation on Microcrack Propagation Behavior of Heterogeneous Rock under Ultrasonic Vibration Load

The use of ultrasonic technology for rock breaking, with its high-frequency and microamplitude impact load, is anticipated to help overcome the challenges of high economic cost and low rate of penetration in mineral resource exploration. A three-dimensional finite-element model of a heterogeneous granite mineral crystal was created using random Voronoi tessellation and cohesive elements. The distribution of the multipolycrystalline structure was achieved in a proportional manner. Then, the differences between conventional cutting and ultrasonic-assisted cutting in rock breaking were compared. The effects of different vibration frequencies (20–35 kHz) and amplitudes (10–50 μm) on crack propagation, crack size, stress distribution, and energy consumption were investigated. The results indicate that higher ultrasonic vibration frequencies significantly improve crack formation, with enhancements ranging from 25.16% to 44.30% compared to conventional cutting. It is important to note that ultrasonic load plays a crucial role in enhancing rock-breaking efficiency by enlarging crack sizes and increasing the number of intergranular tensile cracks instead of solely increasing the total number of cracks. When the vibration frequency is 30 kHz, the crack volume and the proportion of intergranular tensile cracks reach their peak values, while the cutting force decreases to its lowest point, 74.51% lower than conventional cutting. Increasing the vibration frequency is advantageous for reducing mechanical energy consumption. However, once the vibration frequency surpasses 30 kHz, further increasing it does not significantly enhance the ultrasonic effect. Additionally, raising the amplitude can increase the quantity and size of cracks, leading to an effective improvement in the stress situation of the polycrystalline diamond compact cutter.