Investigation on Fracture Properties of Single-Flawed Tunnel Model Under Medium-to-Low-Speed Impacts

Dynamic fractures occur frequently in geophysical processes and engineering applications. It is thus essential to study crack and failure behaviors, such as crack time-to-initiation, crack growth rate and arrest period under dynamic loading. In this study, impact experiments were implemented by utilizing the single-flawed tunnel specimens under drop-hammer impacts. Four brittle materials, i.e., green sandstone, red sandstone, black sandstone and polymethyl methacrylate, were selected to make single-flawed tunnel specimens. Strain gauges and crack extension gauges were employed to measure the crack extension parameters. The properties of crack growth rate, crack time-to-initiation and arrest period of these four brittle materials were discussed and analyzed. The corresponding numerical simulation was performed by using the commercial software AUTODYN. The numerical results of crack growth rate and crack time-to-initiation agreed with the impact test results. The commercial software ABAQUS was applied to compute the dynamic stress intensity factors. The results show that both the dynamic initiation fracture toughness and the crack growth rate increase with the elastic moduli of these four types of brittle materials under the same loading conditions, whereas the crack time-to-initiation decreases with the increase in elastic moduli of the brittle materials under the same loading conditions.