Experimental investigation of the effect of strain rate on the cracking behaviour and acoustic emission characteristics of red sandstone containing orthogonal cross flaws under quasistatic uniaxial compression

The loading rate markedly influences the mechanical response characteristics and failure mechanisms of flawed rocks. To scrutinize the effects of strain rate on fundamental mechanical properties, cracking behaviour, and acoustic emission (AE) characteristics, a comprehensive experimental study was conducted on red sandstone specimens containing orthogonal cross flaws, subjected to uniaxial compression at varying quasi-static strain rates. Additionally, a numerical investigation utilizing the PFC2D was performed to elucidate the fracture mechanism. The results reveal that strain rate has a significant effect on peak strength, elastic modulus, peak strain, and crack initiation stress in specimens, with a discernible upward trend observed in these parameters as the strain rate escalates. However, the impact of strain rate on specimen crack initiation location is minimal, and it significantly correlates with the primary flaw inclination angle alpha. Across four groups of strain rates, specimens with identical alpha exhibit nearly identical crack initiation positions and crack initiation types. The accumulative AE energy, AE counts, and overall AE b-value exhibit a decreasing trend with escalating strain rates. Analysis of RA and AF values shows a gradual increase in shear crack proportion with increasing strain rates. Moreover, the normalized time for the continuous decrease in the real-time AE b-value remains around 0.8. Furthermore, the changes observed in the particle contact force chain field and stress nephogram indicate that flaw tips characterized by significant regions of tensile stress concentration tend to initiate new cracks first.