13. New Technology Applications
The potential advantages of using electromagnetic acoustic transducers (EMATs) for nondestructive evaluation of metal parts have been known for some time. Recently a generically new EMAT has been perfected which can generate and receive horizontally polarized shear (SH) wave andle beams. SH waves offer considerable advantages over SV waves for inspecting metal parts of complex shape: 1) they reflect specularly from planes containing the direction of particle displacement, 2) they can be generated in any direction lying· in the saggital plane with equal efficiency, and 3) SH wave transducers inherently discriminate against Raleigh, L and SV waves. These advantages make SH waves particularly useful for weldment inspection. A brassboard system was assembled for locating natural and simulated flaws in thick MIG welds, and a new technology for placing controllable defects in weld deposits was developed. It was then shown that the SH-wave inspection system was capable of producing an accurate map of the controllable defects introduced into the weld deposit. The ultrasonic map compared well with the notes taken by the welder and contained considerably more detail than the radiographic map. The inspection was performed at 1.7 MHz with the SH wave beam axis inclined at approximately 38° with respect to surface normal. Tungsten and alumina rod inclusions as small as 3/32 inch in diameter with localized within the weld deposit with signal-to-noise ratios of better than 10 dB and the inspection was performed on an "as-welded" sample without surfaces preparation through surface grinding or polishing.
Fortunko, C. M. and Lawrence, W. E., "Weld Inspection with Shear Horizontal Acoustic Waves Gnerated by EMATs" (1980). Proceedings of the DARPA/AFML Review of Progress in Quantitative NDE, July 1978–September 1979. 79.