A Generalized Model of the Effects of Microstructure on Ultrasonic Backscattering and Flaw Detection

The influence of microstructure on ultrasonic inspection is well known. Familiar examples include the attenuation of ultrasound due to scattering from grain boundaries and the anisotropies in velocity that are associated with preferred grain orientation. Less commonly discussed are the creation of backscattered noise, which can mask flaw signals, and the modification of transducer radiation patterns, e.g. the modulation of the phase fronts in a beam, which can cause fluctuations in signals reflected from surfaces [1]. The latter influence the measurement of attenuation as well as the strength of signals reflected from flaws. The goal of this work is to develop a unified basis for understanding these phenomena, as can be used in the analysis of the performance of ultrasonic flaw detection systems. Of interest are correlations of noise in time as well as the variance of noise signals (about their mean of zero) and reflected signals (about a non-zero mean).