Abstract: In compound multilayer structures, a subsurface crack whose orientation is vertical to layers is hard to detect. Unfortunately, the mechanical properties of a multilayer structure are significantly influenced by this very kind of flaws, which raise the need of a reliable NDT method for them. For copper-steel layered structures, the Stoneley’s secular equation of the interface is solved by means of theoretical analysis, and the theoretical velocity of the attenuated interface wave is acquired. Efforts are also made in analyzing the propagating characteristics of oblique incident ultrasounds to multilayer structures, and a theoretical method of exciting interface waves on copper-steel interface is proposed. In simulating experiments, a interface wave is obtained by making the ultrasound propagate obliquely onto the medium of copper-steel structure with selected angle. The experimentally measured velocity of the interface wave accords well to the calculated one. Furthermore, the mentioned interface wave is applied to the examination of artificial cracks in copper-steel bead welded structures, and it is shown that this method is capable of detecting this kind of cracks with relatively high sensitivity.

Key words: Copper-steel welding, Crack, Interface wave, Multilayer structure