Dynamic photoelastic experimental study on the influence of joint contact area ratio on stress wave propagation

The presence of rock joints significantly affects not only the propagation of stress waves but also the safety of underground engineering. The purpose of this study is to non-destructively observe the stress concentration around the joints and the characteristics of stress wave propagation. The test on specimens consisting of two contacted polycarbonate plates with an artificial joint was carried out using a modified Split Hopkinson Pressure Bar(SHPB) and a photoelastic equipment. In order to reduce the wave impedance of loading bars, the input and output bars of SHPB equipment were made of polycarbonate materials. The dynamic photoelastic experiment figures and propagation characteristics of the stress wave were studied according to the theory of viscoelastic wave propagation and the concept of energy flow density. Then, the relationship between the energy flow density of the transmission wave and the stress concentration near the joints with different contact area ratios and joint distribution forms was analyzed. The test results show that with decreasing the contact area ratio, the stress wave transmission coefficient decreases while the energy flow density of the transmission wave as well as the stress concentration near the joints increases. When the contact area ratio remains constant, the more dispersed the joints, the greater the stress wave transmission coefficient. In this case, the energy flow density of the transmitted wave increases while the stress concentration near the joints attenuates. Under a dynamic load, the stress concentration phenomenon appears near the joints, and the energy flow density of the transmission wave is closely related to the stress concentration near the joints. © 2021, Science Press. All right reserved.