Conventional drilling of rocks can generate significant damage in the drilled material; a material layer is often split off a back surface of a sample during drilling, negatively affecting its strength. To improve finish quality, ultrasonically assisted drilling (UAD) was employed in two rocks - sandstone and marble. Damage areas in both materials were reduced in UAD when compared to conventional drilling. Reductions in a thrust force and a torque reduction were observed only for UAD in marble; ultrasonic assistance in sandstone drilling did not result in improvements in this regard.
Mikhailova, N. V., Onawumi, P. Y., Roy, A., & Silberschmidt, V. V. (2018). Ultrasonically assisted drilling of rocks. In AIP Conference Proceedings (Vol. 1959). American Institute of Physics Inc. https://doi.org/10.1063/1.5034699