Effect of loading rate on energy and acoustic emission characteristics of tensile fracture and shear fracture for red sandstone

Abstract

To understand the influences of loading rates (LRs) on the energy and acoustic emission (AE) characteristics during tensile fracture and shear fracture, a series of pure mode I and pure mode II fracture tests were carried out under different LRs using the semi-circular bending (SCB) and single-notched shear-box (SNSB) sandstone specimens. The AE technique is employed to obtain the acoustic signal generated from rock fracture. Results show that: (1) The mode I fracture toughness KIC and mode II fracture toughness KIIC increase logarithmically with the increase of LRs, and the ratio of KIIC to KIC changes in the range of 2.1–2.3 at different LRs; (2) The cumulative AE energy (EAEI and EAEII) increases with LRs in a power function relationship under two loading modes, and the ratio of EUAEII and EUAEI (the released AE energy per unit fracture area) at different LRs varies from 38 to 46; (3) The cumulative input energy (ECII and ECI) increases logarithmically with the increase of LRs, and the ratio of EUII to EUI (the total released energy per unit fracture area) at different LRs ranges from 49 to 54. The LR has a significant effect on the RA-AF distribution characteristics. The quantitative analysis shows that the proportion of shear cracks increases but the proportion of tensile cracks decreases with LRs under two loading modes. Finally, the relationship between fracture toughness and tensile strength of red sandstone is discussed.