Rock dynamic compressive strength is a most important parameter to evaluate the structural stability. In this study, FEM based numerical code RFPA3D was employed to investigate the inertia and friction effects on the rock dynamic compressive strength using three-dimensional SHPB numerical testing system. Different rock samples, including the solid cylindrical ones with different length to diameter ratios and the ring shaped ones with different inner diameters, were utilized to analyze the axial and radial inertia effects. The friction effect along the interfaces between rock sample and bars was investigated by setting different interfacial static friction coefficients. Simulation results demonstrated that the rock dynamic compressive strength increases with increasing length to diameter ratio or decreasing inner diameter of the testing sample. In addition, the radial inertia effect has a higher impact on the enhancement of the rock dynamic compressive strength compared with the axial one. Moreover, the friction effect along the interfaces between rock sample and bars directly alter the stress state at the rock sample end during the SHPB tests, which further improve the rock dynamic compressive strength. The findings in this study provide a better understanding of the inertia and friction effect on the rock dynamic compressive strength.
The split Hopkinson pressure bar (SHPB) system is widely utilized to test the rock dynamic behaviors. And previous studies have revealed that the rock dynamic compressive strength increases with increasing strain rate (Zhang and Zhao, 2014; Zhao et al., 1999; Li et al. 2005). However, it should be noted that the inertia and friction effects are also involved during the SHPB tests, which may affect the derived rock dynamic compressive strength (Gorham, 1989; Zhu et al., 2016).
The inertia effect is associated with most dynamic events, and can be detailedly divided into axial and radial items in SHPB tests, respectively. A suitable length to diameter ratio testing sample can effectively reduce the axial inertia effect. Davies and Hunter (1963) suggested that the axial inertia effect during the SHPB tests could be obliterated when the length to diameter ratio of the testing sample equals to (equation), where the parameter γ refers to the Poisson's ratio. For the radial inertia effect, Forrestal et al. (2007) pointed out that the radial inertia effect is largest along the centerline of testing sample, while becomes zero at the surface. However, it should be noted that both of findings above were failed to consider the rock heterogeneous behavior.
