Computation of Grain-Noise Scattering Coefficients for Ultrasonic Pitch/Catch Inspections of Metals

One limiting factor in the detection of internal defects in metals is so-called 'grain noise' which arises from the scattering of sound by microstructural boundaries. For pulse/echo inspections, independent-scatterer models have been developed and applied successfully to predict backscattered grain noise characteristics in many situations of practical importance. Here we consider the extension of the independent-scatterer noise models to pitch-catch geometries. In this first of several planned papers, we focus on the evaluation of the scattering coefficient η which is a property of the microstructure alone and quantifies its capacity for generating grain noise. A general scheme for evaluating η is first laid out. Then, for simple single-phase cubic and hexagonal metals, formulas are developed which express η in terms of the single-crystal elastic constants and the mean grain diameter for various combinations of the incident and scattered wave types