Acoustic emission for materials processing: a review

Abstract Acoustic emissions are the elastic waves emitted by sudden localized changes in stress from, for example, the formation of cracks, plasticity and phase transformations. It is beginning to be considered a potential in-process monitoring technique for quality and productivity improvement as a sensor for closed-loop feedback control systems. Applications of the technique are held back because of its complicated nature and because the signals are controlled rather subtly by microstructure. In this review we describe the theoretical framework that has begun to emerge and which now provides a physical understanding of acoustic emission. We then reconsider the results of laboratory studies and recent applications to assess, in the light of this understanding, the contribution that acoustic emission methods might make toward in-process monitoring and microstructure control during metals processing.