An experimental investigation on fatigue characteristics of granite under repeated dynamic tensions

Abstract

Rock engineering is prone to fatigue failure under cyclic disturbances caused by repeated dynamic loadings such as earthquakes, blasting and impacts. These cyclic dynamic loadings could be tensile under repeated implosions , excavation induced unloading and reflection of compressive waves at free surfaces or interfaces. However, compared with cyclic dynamic compression, the rock fatigue characteristics under cyclic dynamic tension remain poorly understood. To investigate the dynamic tensile fatigue characteristics of rock, cyclic dynamic Brazilian tests and direct tension tests were conducted on granite using the split Hopkinson pressure bar and the split Hopkinson tension bar, respectively. The testing results showed that the peak stress of granite decreases, while the peak strain increases with increasing impact number under a given impact stress. The fatigue thresholds of granite in the cyclic dynamic Brazilian and direct tension tests are 0.71 and 0.49 times the critical impact stress, respectively, indicating that the rock is more prone to fatigue failure under dynamic direct tension. The total dissipated energy for fatigue failure of rock increases linearly with fatigue life. The damage accumulation features defined by energy dissipation and strain are distinct, and the damage calculated by strain can display nonlinear characteristics of damage evolution. In addition, with increasing impact stress, the failure surface roughness of the specimens in cyclic dynamic Brazilian tests increases, while that in direct tension tests decreases. The findings in this study could facilitate the understanding of rock fatigue characteristics and provide a basis for stability evaluation and disaster prevention in rock engineering.