Nondestructive evaluation of planar defects in plates using low‐frequency shear horizontal waves

An ultrasonic technique is described that allows the determination of the through‐thickness dimension and limited localization of planar defects (cracks) in an isotropic metal plate. The scattering of horizontally polarized shear (SH) plate waves by edge and buried planar defects is investigated using a variational integral expression. Numerical results are presented that allow the calculation of the SH plate wave signal amplitudes as a function of defect through‐thickness dimension and location within a plate for two‐dimensional cracks. It is shown that SH waves are particularly useful for detecting and sizing of crack‐like defects. In addition, it is demonstrated that in plates, which can support a number of propagating SH plate waves, it is also possible to determine the relative position of a defect from interference phenomena. The numerical results are confirmed experimentally using an electromagnetic‐acoustic transducer system to generate and detect 454‐kHz SH wave signals along the normal to the ci...