New Development to Measure Mode I. Fracture Toughness in Rock

Abstract

Tensile fracture toughness is one of the dominant characteristics of rocks that play an important role in fracture mechanics of rock structures. In spite of the substantial amount of work that has been conducted as suggested methods to determine the fracture toughness of rock in Mode I., research on new methods are still demanded. The compact tension (CT) specimen is widely used to determine the fracture toughness of metals and is a standard method in accordance with ASTM standard. To conduct similar direct tests in rock, preparation of rock specimen a difficult task and needs some special tools to create notched sample. To address these issues, experimental techniques based direct tensile apparatus have been developed. Developed experimental procedure involves the use of the specimens having a central hole and two notches or cracks at both inner side of proposed specimen. The stress intensity factor formula at the crack tip of a CT specimen can be availed through the literature. However a new expression of stress intensity factor is needed for the developed test in order to account geometry and loading configuration. To develop a new stress intensity factor expression, the numerical models of suggested method were worked out. The focus of the current work is on development of the experimental technique, which involves determining the optimum sample size and shape, loading procedure, fracture toughness for different rock types, and verification of suggested method based on CT test which has been carefully considered in this investigations.