Differential Response of Fracture Characterization of Mode III Fracture in Sandstone Under Dynamic Versus Static Loading

This work examines the effect of loading rate ( $\stackrel{·}{K}$) on the mode III fracture behavior of sandstone. Edge-notched diametrically compressed (ENDC) disc sandstone specimens were tested under different static and dynamic mode III fracture loadings, revealing a clear loading rate effect on both mode III and mode I fractures. Specifically, the peak load and fracture toughness (K_IIIC, K_IC) increase as the $\stackrel{·}{K}$ increases across both static and dynamic scales. At the static scale, the K_IIIC is about 1.28–1.38 times of the K_IC, whereas at the dynamic scale, the K_IIIC is less than the K_IC. The relationship between K_IIIC and K_IC is affected by the loading scale and the shape of the specimen, but the data collected thus far indicate that the origin and type of rock have minimal effect on this relationship. In addition, the fracture surface morphology characteristics were quantitatively analyzed.