Damage Evolution Under Cyclic Dynamic Loading in Rocks During Drilling

Abstract

The damage evolution in rocks under cyclic dynamic loading is critical for optimizing percussive drilling operations in mining, oil and gas, and geothermal applications. This study investigates the progressive fatigue damage in granite, sandstone, and limestone subjected to repeated impact loading using a modified Split Hopkinson Pressure Bar system that simulates drilling stress pulses. Through multi-parameter monitoring including stress-strain response, acoustic emission, ultrasonic pulse velocity, three distinct damage stages were identified: initial compaction, stable crack propagation, and accelerated damage leading to failure. The damage variable, defined via elastic modulus degradation, exhibited a nonlinear sigmoidal increase with cycle number and cumulative dissipated energy, strongly influenced by impact energy, frequency, confining pressure, and rock type. Energy analysis revealed that the dissipation ratio rose sharply from ~0.25 in early cycles to over 0.70 near failure, correlating closely with crack coalescence. These findings link micro-crack growth under repeated compression-tension waves to macroscopic degradation at the bit-rock interface. A power-law damage evolution model is proposed, offering practical implications for predicting rate of penetration, reducing bit wear, and assessing borehole stability. The results advance the understanding of fatigue mechanisms in percussive drilling and provide guidelines for parameter optimization.