Deterioration of dynamic fracture characteristics, tensile strength and elastic modulus of tight sandstone under dry-wet cycles

Under dry-wet cycles, rock mechanical parameters may be degraded with material strength reduced and structure stability weakened. The impact test was conducted with large single cleavage semicircle compression (LSCSC) specimens to investigate the effect of dry-wet cycles on rock crucial parameters including dynamic parameters, fracture toughness, elastic modulus and tensile strength. Crack extending gauges (CEG) were applied to investigate fracture time and crack velocity. The fractal theory was introduced to correct the extended length and the speed of the crack. A RSM-SY5 (T) non-metal ultrasonic detector was employed to measure P-wave and S-wave under different dry-wet cycles. Additionally, the chemical composition and microscopic morphology features of sandstone in different dry-wet cycle numbers were determined by using X-ray diffraction (XRD) and a scanning electron microscope (SEM-TM3000). The dynamic stress intensity factors (DSIFs) were computed by ABAQUS software. The fracture toughness under different dry-wet cycle numbers was confirmed by using numerical-experimental method. The investigation demonstrates that the mode I crack propagation was influenced by the number of dry-wet cycles with the crucial parameters, fracture toughness, material parameters, cracking time and average crack propagation speed affected. The fracture toughness decrease and disperse with the increase of dry-wet cycles. With the increase of dry-wet cycle number, the crack propagation speed increases, and the crack initiation time decreases.