Internal Friction in a Diffuse Field Used as a Measure to Characterize Material Properties

Ultrasonic attenuation values of metals deduced using conventional pulse/echo methods contain contributions from both grain scattering and energy absorption (arising from internal friction). In contrast, the energy loss mechanisms, which contribute to diffuse field measurements, are believed to be insensitive to scattering, and hence provide information on internal friction only. In this work several metal specimens are studied, some of which have attenuation values in good agreement with the predictions of grain-scattering models, and others which do not. The diffuse field decay rate of each specimen is measured, and used to deduce Q inverse, which is a measure of the internal friction in a material. The comparison of the attenuation and diffuse field measurements indicate that specimens in which the measured and predicted values of attenuation were not in good agreement have a significant internal friction contribution towards attenuation, indicating that absorption and not grain scattering is the dominant attenuation mechanism