Mechanism of rock fatigue damage in terms of fracturing modes

A novel outcome of the research described is the observation of the effect of indirect tensile cyclic loading on the fracture toughness (KIC) of rocks. A maximum reduction of the static KIC of 46% was obtained for the highest amplitude dynamic cyclic loading test. A second series of cyclic tests showed that the 45° and 70° inclined chevron notch cracks opened from the beginning of the cyclic loading test, whereas under monotonic loading, the chevron notch cracks closed up to failure. When compared with static rupture, the detailed scanning electron microscope (SEM) examinations showed that fatigue damage in Brisbane tuff is strongly influenced by the failure of the matrix, due to both intergranular fracturing and transgranular fracturing, whereas smooth and bright cracks were formed along cleavage planes under static loading.