The damage and failure mechanism of prestatically loaded rock during medium‐strain rate cyclic impact loading

Abstract To study the rock damage mechanism under high static loading and superimposed medium strain rate cyclic impact loading, a series of tests were carried out. First, the rock was preloaded with a static load (27.5, 32.5, 37.5, 42.5 MPa), and then cyclic impact loads with different peak values (6, 8, 10, 12 MPa) and different frequencies (0.5, 1.0, 1.5, 2.0 Hz) were continuously applied until the rock failure. The test results show that the axial strain of the preloaded rock with a static load during cyclic impact follows an inverted S‐shaped pattern. This pattern begins with cracks compacted and closed, then crack gentle development, and finally high‐speed crack expansion. The severe degree of the rock failure process is mainly related to the number of cumulative cyclic impacts. Analysis suggests that the greater the cumulative cyclic impact number, the greater the energy transmitted and dissipated at the tips of rock pores and fractures, making the propagation path of the main penetrating crack more complex. Furthermore, the shorter the rock failure duration, the greater the fractal dimension of the crack/fragments. The cumulative cyclic impacts number is negatively correlated with static load and impact peak, and positively correlated with impact frequency. Based on test results, a rock damage accumulation model under cyclic impact loading was developed. This model uses the inverted S‐type logistic inverse function and considers factors like preapplied static load, impact peak, impact frequency, and the number of impacts. The theoretical calculation results are compared with the damage factors derived from axial strain test data, verifying the reliability of the damage accumulation model.