Reflection behaviour of SH0 from small defects in thin sheets, with application to EMAT inspection of titanium

Abstract

Defects can arise within the weld during the laser welding process of thin titanium sheets, and it is critical that these defects are detected. Shear horizontal (SH) waves offer good potential for defect detection, but require an understanding of how the ultrasonic waves interact with defects, in order to develop an optimised inspection setup, increasing the probability of defect detection. The geometry of a defect strongly affects the reflected signal magnitude, with finite element simulations showing that defect width and length determine the maximum SH0 wave reflection. Experiments confirm this behaviour. The defect width is shown to affect the reflection behaviour due to wave interference. Phase differences between the front face reflection and back face reflection cause a shift in the peak position. In addition, the experimental work presented in this paper also shows the potential for electromagnetic acoustic transducers to be used for the inspection of titanium components.