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.