Identifying failure through locations of acoustic emission

Failure of such materials as dense or overconsolidated soil, rock, and concrete is associated with a zone of localized deformation, where the failure plane develops by a coalescence of damage in the form of pores and microcracks. As damage initiates and propagates, transient elastic waves are emitted from the sudden release of energy. These microseismic events are called acoustic emission (AE). The acoustic sources can be located through the first arrival of the waveform, the P-wave component, recorded by an appropriate data acquisition system. The source location can help identify the eventual failure plane well before it is visible. In this study, an acoustic emission system with eight channels of recording was used to monitor the failure process in rock specimens under uniaxial compression and four-point bend loading. Failure was controlled by conducting the experiments in a closed-loop, servohydraulic load frame. The sources were located using a nonlinear regression technique. From calibration studies, where artificial events were generated at known locations, an accuracy of 1 to 3 mm (about 1 to 3% of the travel distance) was demonstrated for laboratory specimens. For both loading configurations, a clustering of AE locations identified the zone of localized deformation prior to the limit load and before any visible sign of failure.