Global–local model for three-dimensional guided wave scattering with application to rail flaw detection

Abstract

This study presents a three-dimensional global–local formulation for the prediction of guided wave scattering from discontinuities (e.g. defects). The approach chosen utilizes the Semi-Analytical Finite Element method for the “global” portion of the waveguide, and a full Finite Element discretization for the “local” portion of the waveguide containing the discontinuity. The application of interest is the study of guided wave scattering from transverse head defects in rails. Theoretical scattering results are impossible to obtain in this case for a wide-frequency range. While three-dimensional Semi-Analytical Finite Element–Finite Element models for guided wave scattering studies have been used in the past, this is the only study where guided waves in rails were modeled in a wide-frequency range (up to 180 kHz). A comparison analysis with a benchmark study of wave reflections from the free end of a cylindrical rod is conducted first. For the case of the rail, selected case studies of incoming guided modes were chosen, and reflection and transmission spectra are calculated for head defects of various sizes. This kind of results can be utilized to guide and/or interpret ultrasonic guided wave tests aimed at defect detection or quantification. Finally, parametric studies are conducted to examine more closely the role of certain operational parameters that are important in this kind of analysis, and specifically the size of the “local” region and the number of guided modes considered. These parametric studies lead to compromises that need to be struck on the basis of conservation of energy among all wave modes involved.