Comparison of ultrasonic signals in aircraft skin obtained through experiment and simulation

An ultrasonic pulse-echo technique is used to detect disbonds in adhesive bonds in lap joints and those between aircraft skin and reinforcing doublers. Experimental signals are acquired from fabricated as well as commercial aircraft lap joints. It is observed that the ultrasonic signals from unpainted surfaces contain clearly distinguishable echoes from successive layers of the sample. A better understanding of the signals is obtained from sound propagation in multilayered structures. Good correlation between simulation and experimental signals is obtained for both bonded and disbonded locations in the test region. Infrared thermometry is also used to image the regions that are tested ultrasonically. The ultrasonic results are found to be in good agreement with results using thermography