Acoustic Emission Phenomena
AE is commonly defined as transient elastic waves within a material, caused by the release of localized stress energy. Hence, an event source is the phenomenon which releases elastic energy into the material, which then propagates as an elastic wave. Acoustic emissions can be detected in frequency ranges under 1 kHz, and have been reported at frequencies up to 100 MHz, but most released energy within 1 kHz to 1 MHz. Rapid stress-releasing events generate a spectrum of stress waves starting at 0 Hz, and typically falling off at several MHz.
The three major applications of AE techniques are: 1) source location - determine the locations where an event source occurred; 2) material mechanical performance - evaluate and characterize materials/structures; and 3) health monitoring - monitor the safety operation of a structure, i.e. bridges, pressure containers, and pipe lines, etc.
AE can be related to an irreversible release of energy, it can also be generated from sources not involving material failure including friction, cavitation and impact.
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