MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
Correcting the Ultrasonic Scattering Attenuation Coefficient of a Metal Using an Equivalent Medium Layer
Xiaoqin HanXiongbing LiYongfeng SongPeijun NiYiwei Shi
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2016 Volume 57 Issue 10 Pages 1729-1734

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Abstract

The surface roughness and diffraction attenuation of a metal have an effect on the measurement accuracy of the ultrasonic scattering attenuation coefficient. In order to correct the scattering attenuation coefficient, the rough surface of the sample and its neighbouring couplant are assumed to be an equivalent medium layer, namely the sample is a multi-layered medium composed of a layer of the substrate medium and two layers of equivalent mediums. Based on the Lommel diffraction correction coefficient and the parameters of the equivalent medium layer, the expressions are developed for a circular planar piston transducer's sound field in a multi-layered structure with equivalent medium layers. As a result, a correction model of the scattering attenuation coefficient is established by using the surface roughness and diffraction attenuation. AISI 304 stainless steel samples with different surface roughnesses are used to conduct the ultrasonic experiment. The results show that the attenuation coefficient without correction increases in proportion to the roughness; and the average relative error is up to 182.8% compared to the theoretical attenuation coefficient, while the average relative error is only 1.28% after correction. This indicates that the model can limit the negative effects of the roughness and the sound field diffraction on the extraction of the scattering attenuation coefficient. Consequently, the corrected attenuation coefficient can improve the accuracy and reliability in the nondestructive evaluation of the microstructure.

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© 2016 The Japan Institute of Metals and Materials
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