Optical technique for examining materials' elastic properties

摘要

In this work we present a successful non-contact ultrasound laser generation and detection system for the extraction of the structural properties on mechanical structures. The system uses a Q-switch Nd:YAG short pulse high power laser to generate a broadband source of Lamb waves that propagate along the plate, interacting with the structure's entire thickness. A modified Michelson surface displacement optical fibre interferometer is used for the detection of the stress and strain waves. In order to extract the structural information stored in the generated and detected waves we present two completely different signal processing tools; the reassigned spectrogram as a time - frequency analysis and the two dimensional Fourier transform. We compare these two techniques and extract interesting conclusions of their properties. Finally we apply these two techniques and the developed system to temperature change sensitivity and damage detection applications.