Dynamic shear fracture and SEM study of granite and marble

The dynamic shear fracture characteristics and mechanisms are studied, by utilizing a novel triaxial split Hopkinson pressure bar (3D-SHPB) and a modified configuration of punch-through shear samples. Two types of rocks with similar uniaxial compressive strength are chosen; one is granite which is an igneous rock that is polymineralic, the other is marble which is monomineralic and relatively homogeneous. The mineral content and grain structure of two rock types are identified using petrographic thin sections. The strain rate effect of rock shear strength under triaxial confining conditions has been studied by controlling the impact velocity of the striker. Both rock types exhibit strain rate effect with increasing shear strength; granite has higher shear strength and failure strain, while marble has lower shear strength and strain. The microscopic characteristics of dynamic shear fracture for different rocks are examined using scanning electron microscope. Different minerals undergo different failure modes during dynamic shear fracturing, as identified by SEM studies on the fracture surfaces.