Ultrasonic measurements for the quantitative NDE of adhesive joints-Potential and challenges

The use of adhesive bonding in safety-critical applications is currently retarded by the lack of a satisfactory non-destructive test for the quality of the adhesive/adherend interface. Possible ultrasonic approaches to this problem are reviewed. It is shown that there are two promising techniques, i.e., measurement of the reflection coefficient amplitude from the adhesive/adherend interface and measurement of the frequencies of the zeros of the reflection coefficient from the adhesive layer. Measurement of the collection coefficient zeros is much simpler and more reliable than reflection coefficient amplitude measurements. However, the reflection coefficient zeros are more sensitive to small variations in the adhesive layer properties than to relatively large changes in the interlayer. Reflection coefficient amplitude measurements may be more successful in practice