9. Defect Characterization: Fundamentals
My objective is to help develop a quantitative working model for a typical nondestructive testing system. Specifically, our objective is to relate the parameters which characterize a defect s~ch as size, orientation, and shape to the ultrasonic scattering field parameters such as amplitude, frequency, scattering angle, and polarization or mode conversion. In Fig. 1 is shown a flat surface sample immersed in liquid containing a real flaw a certain distance below the surface; i.e., in the bulk of the material. Sound waves propagate through the liquid and for the simplest case the wave front enters such that only incident longitudinal waves are present. The waves .at the flaw are scattered, and also mode converted; the scattered wave, which will now be both shear and longitudinal will be reconverted back to a longitudinal wave once leaving the solid body and picked up by a receiver oriented at some angle.
Adler, Laszlo and Lewis, Kent, "Models for the Frequency Dependence of Ultrasonic Scattering from Real Flaws" (1977). Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE, July 1975–September 1976. 38.