Fracture failure analysis of elliptical hole bored granodiorite rocks under impact loads

Abstract

The aim of the present study is to evaluate the dynamic failure process of granodiorite rock including an elliptical hole. A series of experimental tests including both static and dynamic loads at four different loading rates was conducted on the samples. Dynamic cyclic loading testing was also applied to evaluate the fatigue behaviour of the rocks. The failure process was clearly recorded by a high-speed camera. The distribution of dynamic stress and energy density around the elliptical hole was numerically investigated using LS-DYNA. Thin-section surveying and scanning electron microscope (SEM) analysis were also used to evaluate response of different minerals during failure process and show the microcrack evolution in this type of rock. The results indicate that an elliptical hole in granodiorite rock leads to obvious stress concentration and energy accumulation which can cause considerable decreases in the strength parameters. Moreover, the dynamic strength and elastic modulus exponentially increased with an increase in the loading rate. The high-speed camera results indicate that the visible cracking and severity of the rock failure also increased with an increase in the loading rate. During cyclic Split Hopkinson pressure bar (SHPB) tests with decreasing striker velocity, the fracture nature was transformed from shear to tensile. Cleavage planes controlled the fracture evolution, which was detected in both the thin-section and SEM analyses.