Combined numerical and experimental studies on the dynamic and quasi-static failure modes of brittle rock

Loading rate affects not only the mechanical properties of rock but also the cracking behaviour or the failure mode. Firstly, experimental studies on the mechanical properties and the related cracking behaviour are studied based on the Carrara marble specimens containing a preexisting flaw under different loading rates. The result shows that both the compressive and tensile strengths are rate-dependent but with different sensitivities to strain rate. Meanwhile, the cracking processes of the single-flawed specimens are also found to be rate-dependent with the aid of an ultra-high-speed video system. Secondly, to investigate the mechanism behind the experimental phenomena, a material model based on the experimental strength data is proposed and applied to the numerical model. The influence of the rate-dependent strength on the cracking behaviour is studied comprehensively by using the 2D and 3D explicit dynamic FEM code. The numerical results reveal how the rate-dependent strength affect fracturing behaviour, as well as the failure stress of the single-flawed specimen. The plastic zones do not equal the damaged zone or the cracks. The dynamic loadings lead to the "X" shaped failure mode of the singleflawed specimen regardless of the flaw inclination angle. In contrast, the quasi-static loadings lead to the diagonal failure mode. It indicates that shear displacement dominates the whole cracking process under dynamic loadings, while it only dominates the failure period under quasi-static loadings.