13 May 2000 Noncontact ultrasound studies of composite materials: new developments
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Techniques are being developed worldwide for non-contact ultrasonic inspection of composite materials. These include laser generation and optical detection of ultrasound; both with interferometers and simpler beam deflection techniques, air coupled transducers are also used as generators and/or detectors of ultrasound. This paper compares the generation efficiency and damage thresholds of a range of different laser types: A fundamental Nd:YAG laser (1.06 micrometer), a TEA CO2 laser (10.6 micrometer normally preferred for carbon- fiber reinforced composites) and a Nd:YAG laser with an Optical Parametric Oscillator (OPO) tunable up to 4 micrometer. The laser energy is absorbed with the optical absorption depth, the temperature rise is affected by the wavelength and laser pulse duration. It is essential to remain in the thermoelastic regime in order not to damage the material. A modified Michelson interferometer is used to detect the absolute displacement of the ultrasound. Optical beam deflection techniques and air-coupled transducers are also evaluated as detectors.
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Christopher Edwards, Christopher Edwards, Theodosia Stratoudaki, Theodosia Stratoudaki, Stephen Dixon, Stephen Dixon, Stuart B. Palmer, Stuart B. Palmer, } "Noncontact ultrasound studies of composite materials: new developments", Proc. SPIE 3993, Nondestructive Evaluation of Aging Materials and Composites IV, (13 May 2000); doi: 10.1117/12.385498; https://doi.org/10.1117/12.385498

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