Fundamental fracture modes of granite using new testing devices

The paper presents an investigation on fundamental fracture modes of granite, using new testing devices in order to highlight the salient features of fracture processes in granite such as path dependence (mode I tension fracture, mode II shear fracture and mode ΙΠ torsion fracture), and shear transfers due to aggregate interlock (crack dilatancy), cross effect (frictional contact slip). Experimental results provided useful mechanical characteristics such as cracking strength, stiffness, and fracture energy according to the three fundamental fracture modes, and particularly the Hillerborg characteristic length of granite in tension readily derived from direct tension testing. Computerised X-ray tomography analysis evidences localisation of cracking in specimens subject to different fracture modes, and finally a non destructive ultrasonic technique has been used to detect the occurrence of damaging non linearities.