CHARACTERIZATION OF FATIGUE CRACK EXTENSION BY QUANTITATIVE ACOUSTIC-EMISSION

Acoustic emission is the term used to describe the spontaneous release of transient elastic waves in solids as a consequence of sudden localised changes in stress. A calibrated four-channel elastic wave recording system has been used to detect and characterise acoustic emission events associated with the growth of a fatigue crack in a compact tension specimen of 7010 aluminum alloy. The transducers sampled the elastic wave field in four independent directions in a plane perpendicular to the crack. The 2-D force dipole representation of each event, assumed to be a point source, was deduced by inversion of the Green's tensor. Each emission event was then characterised in terms of source type (e. g. , microfracture, slip), orientation relative to fatigue crack and size (e. g. , crack volume).