Temporal dominant frequency evolution characteristics during the fracture process of flawed red sandstone

Abstract

To study the time-varying dominant frequency distribution characteristics during the cracking process of intact and flawed rocks, uniaxial compression tests are carried out on three types of red sandstone specimens. Both acoustic emission (AE) and photographic technologies are performed to monitor the real-time cracking process of tested specimens. The relationship between the AE rate curve, the axial stress-time curve and the cracking process is first analyzed, which can be employed to evaluate the microscopic and macroscopic deformation characteristics of rocks. The time-varying dominant frequency and amplitude distribution characteristics in different cracking stages of tested rocks are investigated. Four modes of AE signals, i.e., AE signals with low-frequency and high-amplitude (LF-HA), AE signals with low-frequency and low-amplitude (LF-LA), AE signals with intermediate-frequency and low-amplitude (IF-LA) and AE signals with high-frequency and low-amplitude (HF-LA), are found. The coupling application of four modes of AE signals extracted from unstable deformation stages can be viewed as early warning for unstable failure of rocks. The fracture mechanism of intact and flawed rocks is discussed based on the statistical characteristics of dominant frequency during the cracking process. Micro-shear cracking mainly dominants the ultimate failure of all of tested rocks.