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Acoustic emission

: Große, C.U.; Wanner, A.; Kurz, J.H.; Linzer, L.M.

Busse, G.:
Damage and its Evolution in Fiber-Composite Materials : Simulation and Non-Destructive Evaluation
Stuttgart: ISD Verlag, 2006
ISBN: 3-930683-90-3
Aufsatz in Buch
Fraunhofer IZFP ()
acoustic emission; wireless sensor network; monitoring; moment tensor inversion; localization

In analogy to earthquakes, acoustic emissions (AE) can be considered to be a form of microseismicity generated during the failure process as materials are loaded. AE are defined as the spontaneous release of localized strain energy in stressed material.
This energy release can be due to, for example, micro-cracking in the material and can be recorded by transducers (sensors) on the material's surface. An advantage of AE techniques, compared to other Non-Destructive Evaluation (NDE) techniques, is that damage processes in materials being tested can be observed during the entire load history, without any disturbance to the specimen. Ultrasonic analysis techniques, for instance, have to be applied in conjunction with scanning techniques to detect a defect.
In contrast, AE studies require only a few sensors, located at different positions on the surface of the material to record the elastic waves radiated by a crack under stress, to image the crack. The stress field in the specimen being tested is related to the applied force. When a material is stressed, the deformations are controlled by what is known as the constitutive behavior of the material.
For example, some materials respond to stress linear elastically, and others behave elasto-plastically.
The linear elastic stress-strain relationship is called Hooke's law. AE, however, are more strongly dependent on the irreversible (non-elastic) deformations in a material. Therefore, this method is only capable of detecting the formation of new cracks and the progression of existing cracks or friction processes. These phenomena are often related to internal mechanical or thermal loads or pressures applied from outside the specimen. AE tests can be conducted under normal, service conditions or during a slight enhancement of the load. Therefore, it is an extremely useful method in testing structures under real load conditions to record a possible failure process.