Broadband Lamb-wave measurements for materials characterization

S. Gareth Pierce; Q. Shan; Brian Culshaw; C. Wolters; Keith Worden

doi:10.1117/12.316962

21 July 1998 Broadband Lamb-wave measurements for materials characterization

S. Gareth Pierce, Q. Shan, Brian Culshaw, C. Wolters, Keith Worden

Proceedings Volume 3330, Smart Structures and Materials 1998: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials; (1998) https://doi.org/10.1117/12.316962
Event: 5th Annual International Symposium on Smart Structures and Materials, 1998, San Diego, CA, United States

Abstract

Conventional ultrasonic Lamb wave testing of materials often relies on the efficient generation and detection of a single Lamb wave mode that propagates in a relatively non- dispersive region of its characteristic. Such an approach allows identification of defect sites within the material by looking for distinct pulse reflections in the time domain. The fundamental symmetric mode is often utilized due to its low dispersion and relatively high velocity. However, this mode is restricted to a low frequency-plate thickness product where its wavelength may be several tens of millimeters with obvious implications for defect sensitivity. An alternative approach to single mode excitation is to utilize broadband Lamb wave measurements. Since a wider portion of the Lamb wave spectrum is now excited it is anticipated that defect resolution could be enhanced. We have investigated the propagation characteristics of ultrasonic Lamb waves in thin plates of metal and composite structure. Ultrasonic generation and detection was accomplished using a combination of non- contacting optical techniques, material integrated optical fiber sensor and conventional piezoelectric sources. Utilizing the broad optical techniques, material integrated optical fiber sensor and conventional piezoelectric sources. Utilizing the broad temporal and spatial bandwidth of a pulsed laser source combined with a point detector, it was possible to simultaneously measure the dispersion characteristics of several propagating Lamb wave modes in both aluminium and carbon fiber composite plates. An alternative approach to signal interpretation was undertaken by developing a NARMAX model of composite plates. An alternative approach to signal interpretation was undertaken by developing a NARMAX model of Lamb wave propagation in a sample plate and correlating properties of the model to damage in the samples. A possible extension to this techniques using a modulated laser diode for acoustic generation is also described. It is anticipated that these related techniques could be used to identify the presence of defects in addition to material ageing effects in composites.

Citation Download Citation

S. Gareth Pierce, Q. Shan, Brian Culshaw, C. Wolters, and Keith Worden "Broadband Lamb-wave measurements for materials characterization", Proc. SPIE 3330, Smart Structures and Materials 1998: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, (21 July 1998); https://doi.org/10.1117/12.316962

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