LASER TECHNIQUES TO CHARACTERIZE THE EFFECT OF GEOMETRY ON ACOUSTIC EMISSION SIGNALS
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abstract
The finite geometry of a laboratory specimen changes a measured acoustic emission waveform because of reflections, transmissions and mode conversions at the interfaces and boundaries of the specimen, thus making it difficult to interpret the measured signal. This paper develops a transfer function that removes these geometric effects from measured acoustic emission signals. This transfer function is developed using a repeatable, broad band (synthetic) acoustic emission source, a pulsed laser, and a broad band, high-fidelity sensor, a laser interferometer. The steps in the development of the transfer function are as follows: an acoustic emission signal is generated and detected in a specimen whose geometry is being characterized; this experiment (same source) is repeated in a `geometry-less specimen,' one that contains no geometric features; and the `geometry-less' signal is divided by the specimen signal (in the frequency domain) to form the transfer function. This transfer function can operate on an acoustic emission signal, measured in the same specimen, but caused by a different source. The accuracy of this transfer function is demonstrated by operating on different acoustic emission sources such as a pencil lead break and removing the unwanted geometric features.
