Understanding rock fatigue Part 1: degradation of rock fracturing resistance under cyclic loading

This study presents the results of laboratory diametrical compression tests performed on Brisbane tuff disc specimens to investigate their mode-I fracture toughness response to static and cyclic loading, as a function of the applied load. Fracture toughness (K) is an important material parameter that corresponds to the critical state of the stress intensity factor required for crack initiation and subsequent propagation. The static and cyclic loading tests were carried out on Cracked Chevron Notched Brazilian Disc (CCNBD) specimens prepared from Brisbane tuff cores. Two different types of cyclic loading were applied: (a) cyclic loading with constant mean level and constant amplitude, termed sinusoidal cyclic loading, and (b) cyclic loading with increasing mean level and constant amplitude, termed increasing cyclic loading. The fracture toughness response to cyclic loading was found to be different from that under static loading in terms of the ultimate load and damage mechanism in front of the chevron crack. A maximum reduction of the static K of 46% was obtained for the highest amplitude increasing cyclic loading test. On the other hand, for sinusoidal cyclic loading, a maximum reduction of the static K of 30% was obtained. These reductions clearly illustrate the dramatic effect of cyclic loading on the fracture resistance of cracks in rocks