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.
