MODEL OF ULTRASONIC NONDESTRUCTIVE TESTING FOR INTERNAL AND SUBSURFACE CRACKS

The scattering of elastic waves in a half-space containing a striplike crack is investigated. As a special case it seems that the crack may be surface breaking. A surface integral equation with the half-space G reen tensor is employed. The key point of the method is the expansion of the Green tenser in Fourier representations with the free part of t he Green tenser expanded in the crack coordinate system and the half-s pace part in the half-space coordinate system. The integral equation i s discretized by expanding the crack opening displacement in terms of Chebyshew functions having the correct square root behavior along the crack edges. The incident field is emitted from an ultrasonic probe an d a recent model for this is employed. The signal response in another (or the same) probe is modeled by a reciprocity argument and the stati onary phase approximation is employed to simplify the final answer, wh ich is thus only valid in the far field of the probes (yielding essent ially a spherical wave). Numerical results are given and are compared with both other methods and with available experiments. (C) 1997 Acous tical Society of America.