DETERMINING THE CYCLIC STRENGTH OF GEOMATERIALS UNDER LOW FREQUENCY CYCLIC LOADING WITH ACOUSTIC EMISSION

Abstract

Acoustic emission is traditionally regarded as an explicit measurable index for microcracking in geomaterials. An accelerative cracking point is first introduced based on the different characteristics of acoustic emission at stable fracture propagation stage. Accelerative cracking point is located between the fracture initiation strength and critical energy release point, a point causing a fatal uncontrolled fracture in materials. Microcracking dominates the real mechanical characteristics in the materials, not reflected on the conventional mechanical experimental results as the stress level beyond the accelerative cracking point at the stable fracture propagation stage. At this stage, non-stress-controlled fracture in materials could arise as that found at unstable fracture propagation stage. Stress-releasing time experiments are also performed for time-dependent concerns. For the stress level equal or beyond fracture initiation strength of materials, the onset stress level gradually decreases below the previous maximum stress level as stress-releasing time increases.