Experimental study on the energy evolution law during crack propagation of cracked rock mass under impact loads

• The energy evolution law and dynamic failure properties during crack propagation of cracked rock mass were studied under impact loads. • The ratios of dynamic energy release rate and energy dissipated for per crack length were calculated. • A Pseudo-coalescence was found and discussed during crack propagation under impact loads. Rock dynamic fracture is usually accompanied by numerous energy loss, to reveal energy evolution laws during rock dynamic fracture, the single cleavage triangle (SCT) specimens made by two types of sandstone are implemented to conduct dynamic fracture tests by using the split Hopkinson pressure bar (SHPB) device. The dynamic stress distribution law and the energy evolution law can be obtained according to the strain history of cracked rock mass subjected to impact loads. Crack propagation gauges (CPG) were applied to measure crack propagation speed, dynamic stress intensity factor (DSIF) and dynamic energy release rate can be determined by using an experimental-numerical method with the help of the software COSMOL. The experimental results show a physical pseudo-healing of the crack due to the short closure of the crack after its arrest under impact loads. The crack propagation speed and the DSIF show a certain oscillatory with the increase of crack length, the DSIFs at crack initiation are 0.2∼0.8 of the maximum value. The history of dissipated energy has a slow decrease after they reach a peak during 300 μs ∼350 μs, whose curves after the peak contain two stages: stage I is that the absorbed energy of the SCT specimen is mainly transformed into the transmitted energy; stage II is that it will be reflected energy. The input energy overtakes the consumed energy by new crack formation to drive the crack propagation and the test results of sandstone specimens show that 2.11 ‰ to 4.44 ‰ dissipated energy is implemented to drive crack propagation. The energy and stress are released more significantly around the crack tip before the crack arrest.