Fatigue Characteristics and Fracture Mechanism of Preflawed Sandstone Subjected to Cyclic Loading

This study comprehensively investigates the fatigue characteristics and fracture behavior of flawed sandstone specimens. Triaxial monotonic and cyclic loading tests are conducted on flawed sandstone specimens with various flaw inclination angles ( β = 0°, 30°, 60°, and 90°). The results indicated that the characteristic stress thresholds increase as β increases. The correlations between flaw inclination angle and peak strength, as well as residual strength, are enhanced under fatigue loading. Irreversible strain, elastic modulus, Poisson's ratio, and fracture behavior are influenced by the fatigue effect, stress level, and flaw inclination angle. In addition, failure modes characterized by wing or antiwing cracks associated with different flaw inclination angles are observed. The crack initiation angle decreases with increasing flaw inclination angle. SEM results demonstrate that the flaw inclination angle exerts a significant influence on microcrack slip, microcrack tip morphology, roughness of the microcrack surfaces, and overall surface roughness of the failed sandstone specimens.