Abstract: The air-coupled ultrasonic C scan technique based on the penetrative opposite side detection mode was utilized to study the inspection of composite multi-layer honeycomb sandwich structure. The result of air-coupled ultrasonic inspection on the triple-layer honeycomb structure was study under the exposed state of honeycomb surface. Meanwhile, the result of air-coupled ultrasonic inspection on the triple-layer honeycomb structure was studied when the honeycomb surface was skinned and compared with the conventional water jet TTU result. The adaptation and reliability of the air-coupled ultrasonic C scan results were proved through the analysis of ultrasonic path and the detection of traditional rays and CR. It was shown that not all bonding interface defects could be detected by the air-coupled ultrasonic technique under the exposed state of honeycomb surface. However, when the honeycomb surface was skinned, compared with conventional water jet TTU, the air-coupled ultrasonic result was not affected by the honeycomb cell being not aligned. And the fast and effective inspection was realized.

Key words: composites, multi-layer honeycomb sandwich structure, bonding interface, air-coupled ultrasonic inspection