Improved acoustic emission locations

Abstract

Acoustic emission locations have been determined in a modest-size specimen of Westerly granite (∼ 50×50×200 mm) under uniaxial compressive loading to failure. Periodically during the experiment acoustic pulses were transmitted from a set of source transducers to an acoustic emission receiver array. Axial and transverse velocities were determined from these transmission data. The piezoelectric transducers used in this study were too large to be treated as points. A separate experiment was performed to determine the effect of finite transducer size and incident angle on observed arrival times. Velocity pulse arrival times were inverted for the known source transducer positions using (1) an isotropic, fixed velocity model, (2) the observed anisotropic, stress dependent velocity field, and (3) transducer size corrections. Incorporation of the observed velocity field and transducer size effects dramatically improved location accuracy. Acoustic emissions were located using this technique. Synthetic data, exact and with realistic “errors,” were inverted to determine location uncertainties at various locations throughout the sample. Suggestions are made for further improvements.