Influence of the strain rate on the deformation and failure of rocks with multiscale cracks

The deformation and failure of rock are affected by the strain rate. However, the effect of the strain rate on rock failure has not been well studied at the microscale level. This study focuses on this complexity by constructing a three-scale wing-shaped crack propagation model that accounts for the interactions between cracks. Based on this model, we determined the initiation and coalescence times of 3 scale levels cracks to reveal the effect of the strain rate on the propagation and failure patterns of multiscale cracks. In addition, we analyzed the critical strain rate (strain rate required for simultaneous coalescence of adjacent scale-level cracks) that leads to failure. The results show that both crack initiation and coalescence times decrease significantly with increasing strain rate and that an increase in initial crack length leads to earlier crack initiation. For the multiscale crack model, as the strain rate increases, large-scale cracks (1-st-scale level cracks) coalesce first, followed sequentially by medium- and small-scale cracks (2-nd and 3-d-scale level cracks). Furthermore, we observed that the critical strain rate initially increases and then decreases with increasing initial crack concentration. Moreover, both an increase in the initial crack length and size decrease factor (ratio of the length of a specific scale-level crack to the length of adjacent larger scale-level cracks) lead to a decrease in the critical strain rate, further confirming the influence of crack size on the failure properties of rock. A comparison with the existing theoretical model shows that the proposed theoretical model is reasonable.