Ultrasonic oblique incidence experiments for interface weakness

Promise for solving the weak interface problem is demonstrated in this paper. Experiments have been conducted using an oblique incidence immersion technique to determine the reflectivity characteristics of good vs weak bonds on various aluminium-epoxy-aluminium specimens. The results showed a frequency dependence of the reflection factor which was predicted by our newly developed interface layer model. Obliquely incident shear waves at 32 degrees showed higher sensitivity to the weaker bonds than the conventional normally incident longitudinal waves. The sensitivity of the shear waves also varied with frequency. It was also found that the relative amplitudes of the echoes from weak bonds with respect to those from good bonds could be reversed at different frequencies. This unusual phenomenon was well explained by the interface layer model.