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16 March 2006 Measurement of coating thickness using ultrasonic resonance spectroscopy
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A technique has been developed whereby the thickness and elastic modulus of a coating applied to a substrate can be calculated from measurement of the resonant bulk wave ultrasonic modes of the combined substrate and coating. The density of the coating and the material properties of the substrate are required for this method. We have investigated the difference between models that take account of material attenuation and simpler models that do not and have found that there is little difference in the predicted resonant frequencies of the system for modes that can be observed in the experimental data. We have applied the technique to explain the experimental measurements for a 100μm thick epoxy resin coating curing on a 1mm thick aluminium substrate using wideband radially polarised SH shear waves. In this dynamic system the elastic properties of the coating change and particular resonant modes not only shift but can disappear or appear in the experimental data. A model is used to explain this behaviour and show that the technique has potential for coating thickness measurement in other areas. We have taken samples of 220μm thick aluminium sheet with a fully cured epoxy coating of nominal thickness 11μm, and have used ultrasonic measurements to calculate the thickness of the epoxy coating layer.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Stuart B. Palmer, Steve Dixon, Ben Lanyon, and George Rowlands "Measurement of coating thickness using ultrasonic resonance spectroscopy", Proc. SPIE 6179, Advanced Sensor Technologies for Nondestructive Evaluation and Structural Health Monitoring II, 61790B (16 March 2006);

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