ABSTRACT
Acoustic emission is a passive inspection technique that uses the elastic waves generated by moving dislocations, cracks, fiber breaks, disbonds, etc. for defect detection and analysis in solids. In metals and concrete, the waves are generated by local stress redistributions associated with the motion of dislocations and cracks (both microscopic and macroscopic cracks). In composites, the stress waves are generated by a variety of actions involving cracking and separation in the fibers and the matrix. Material strain, induced by stress or some other stimulus, is required to release or generate the emissions. Longitudinal and transverse transient displacement elastic waves can be excited by the action of an abrupt local force. A general listing of typical AE sources, classified by material, is as follows:
