Dynamic strength of rocks and physical nature of rock strength

:Time-dependence of rock deformation and fracturing is often ignored. However, the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials, especially for those subject to strong dynamic loadings. In this paper, we investigate the deformation and fracturing of rocks, its physical origin at the microscopic scale, as well as the mechanisms of the time-dependence of rock strength. Using the thermo-activated and macro-viscous mechanisms, we explained the sensitivity of rock strength to strain rate. These mechanisms dominate the rock strength in different ranges of strain rates. It is also shown that a strain-rate dependent Mohr-Coulomb-type constitutive relationship can be used to describe the influence of strain rate on dynamic rock fragmentation. A relationship between the particle sizes of fractured rocks and the strain rate is also proposed. Several time-dependent fracture criteria are discussed, and their intrinsic relations are discussed. Finally, the application of dynamic strength theories is discussed.