A technique for accurate shear wave velocity measurements of thin epoxy resin samples using electromagnetic acoustic transducers (EMATs)

This paper describes an ultrasonic analysis of thin epoxy resin samples using normal incidence radially polarized shear wave electromagnetic acoustic transducers (EMATs). The adhesive thickness in the experiments was approximately 0.5 mm, which is slightly higher than would be expected in an ideal bond, but is the optimum thickness for experimental measurement using shear waves at megahertz frequencies. The epoxy resins examined were supplied in a two-part cartridge form, mixed by injection through a special mixing nozzle. The technique gives an accurate measurement of the shear wave velocity in the thin adhesive layer to within 1.5% error. Indeed the accuracy was high enough to reveal unexpected variations in the elastic properties of the cast resin from a single cartridge, which appear to depend on the order in which the adhesive was extruded from the cartridge.