Acoustic Emission System

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In addition to the mechanical testing, an acoustic emission apparatus will characterize the rupture process of composites or multiphase alloys before the ultimate failure. Acoustic Emission analysis is a non-destructive testing method capable of detecting and locating faults in mechanically loaded structures, components and specimens. AEA provides comprehensive information on the origin of faults in a loaded object and the development of the fault when subjected to continuous or repetitive stress. Acoustic Emission is the term used when defects in metals, plastics and other materials release energy when subjected to mechanical loading. The energy propagates in form of high frequency stress waves. These types of oscillations are then recorded as AE signals on the surface of the specimen. The AE analysis is the characterization of the signals according to intensity and frequency content, and also entails locating the release mechanisms by comparing signal travel times in a measurement procedure using several sensors. The AE Aparatus can stores over 30'000 AE-hits/s or over 2.5 MBytes/s waveform data.

About wavelet transformation:

The department is also developing software and methods for the processing the acoustic signals. The wavelet transformation (WT)method is one of this methods. WT have also opened the door to a flow of new ideas and algorithms that have invaded most traditional fortresses of signal processing. A wavelet transform of an AE signal provides information which wave modes carry significant energy and where in a mode the energy as a function of frequency and time is to be found. Thereby a WT can communicate very useful information. In the following diagram you see an example for a waveform (top) and the corresponding wavelet transform (below). The superposed curves show the result of a dispersion curve calculation (by Vallen Dispersion). The wave modes are identified by arrows.