Experimental study on the temporal and morphological characteristics of dynamic tensile fractures in igneous rocks

In order to investigate the temporal and morphological characteristics of dynamic tensile fractures, experiments on Brazilian specimens machined from igneous rocks (Breccia and Andesite) are carried out with the split Hopkinson pressure bar (SHPB). Detailed observation of the fracture processes of the Brazilian specimens is captured by high-speed camera at a frame rate of 100,000 frames per second. The rate-dependent effect of the dynamic tensile strength of the two igneous rocks is fitted and predicted by the incubation time criterion. Digital image correlation (DIC) is used to calculate the full-field tensile strain distributions on the specimen surface during the loading stage preceding fracture, and this hysteresis of dynamic fracture relative to stress level is interpreted by introducing the concept of incubation time. After the main crack appears, image processing technology is exploited to extract the pixel information of cracks in the high-speed images. Then, FracPaQ quantifies the morphology of the fragmentized process by filling the binarization of cracks with fracture traces. After coordination of the statistical information from these fracture traces, the rose diagram representing their angles and length weights can visually represent the fragmentized characteristics of the Brazilian specimen. Specifically, length-angle distributions of fracture traces at various moments are consistent with the Gaussian function, and the curve fitting parameters reflect differences in the fracture behaviors between the two igneous rocks. In conclusion, the dynamic fracture characteristics of two igneous rocks in dynamic splitting processes are quantified statistically, which can provide references for relevant research.