What is Acoustic Emission ?
Acoustic emission is the technical term for the noise emitted by materials and structures when they are subjected to stress. Types of stresses can be mechanical, thermal or chemical. This emission is caused by the rapid release of energy within a material due to events such as crack formation, and the subsequent extension occurring under an applied stress, generating transient elastic waves which can be detected by suitable transducers. Hence, acoustic emission may be described as the "sound" emanating from regions of localised deformation within a material.
Acoustic emission is a passive listening technique which is extremely sensitive and can detect defects such as a few atom movements. AE can thus provide the early information on defect/deformation in any material or structure. If the atomic bonds break during an integrity test, the energy released propagates through the material according to the laws of acoustics. While this level of sensitivity is important in laboratory research, a less sensitive monitoring system is often used in industry to allow the technique to concentrate on growing defects rather than original deformation. In both instances very, sensitive transducers detect the propagating wave, and the detected waveform can then be subjected to a series of analysis techniques which can be used to detect, locate and identify defects activated by the test program. AE techniques can provide a most sophisticated monitoring test and can generally be done with the plant/pressure equipment operating at, or near, normal conditions. A typical acoustic emission pulse and the more interesting associated parameters are as follows.