Influence of stresses on grain size and attenuation parameters in ultrasonic scattering models

Abstract

Recent findings have shown the dependence of material stresses on the strength of ultrasonic backscatter. The stress dependence arrives when considering the covariance of effective elastic moduli of a medium with a randomly oriented grain structure. In some instances, the change in magnitude of the scattered response due to stress is significant and can be utilized as a technique for NDT stress monitoring. Conversely, ignoring the stress sate could result in significant error when attempting to extract micrsotructural parameters using ultrasonic NDE techniques. This presentation touches on the error generated in estimating the average grain size when using ultrasonic scattering models which include stress dependent backscatter coefficients. Results are given for three scattering modes; longitudinal to longitudinal, shear to shear, and (mode converted) longitudinal to shear under a variety of loading configurations. Furthermore, the stress dependence in the covariance influences common multiple echo attenuation measurements when grain scattering is present. Theoretical attenuation values of the different modes are given for various stress-states. Understanding how stress influences these parameters can potentially improve existing ultrasonic NDT techniques. [Research supported by the Federal Railroad Administration.]