Beam-to-mode conversion in an aluminum plate for ultrasonic nde applications

In a multilayer elastic plate, weak debonding in the horizontal direction parallel to the plate boundaries is insensitive to ultrasonic compressional (P) waves impinging perpendicularly, and can therefore not be detected by conventional vertically oriented reflection schemes. One of the methods for generating along the flaw line shearing stresses, to which the flaw responds, is to orient the input beam obliquely. Unlike vertically impinging beams, multiply reflected oblique beams eventually are converted into guided modes. The horizontal ranges over which the field in the unflawed plate is beam-like or mode-like must be well understood for selection of a diagnostic NDE scheme with “good” features for detection and identification. The present analytical model study explores the conversion and P-SVcoupling processes for an oblique Gaussian P beam input in an aluminum plate. Special attention is given to physical features in the computed data that are relevant for “good” NDE algorithm construction.