Abstract: In the practical test of the composite aramid paper honeycomb sandwich structure, a large ultrasonic attenuation is found in water-squirting through-transmission ultrasonic C-scan detection, while no defects are detected by the pulse echo ultrasonic A-scan method and only a few detects can be identified by the Digital Radiography (DR) method. In this paper, various nondestructive testing methods (such as immersion focused pulse echo ultrasonic C-scan detection, air-coupled through-transmission ultrasonic C-scan detection, reflection infrared detection, shearography, X-ray Computed Tomography (X-CT), etc.) are used to detect the area of large ultrasonic attenuation caused by the through-transmission ultrasonic method. Qualitative localization analyses of most defects are carried out by X-CT detection. The sectional profile of the samples shows that two types of defects in the honeycomb core are the main causes of ultrasonic attenuation in the penetrating method:collapse defects and lattices bubbling defects. These defects are difficult to be detected by X-ray penetrating detection, but they can cause obvious attenuation in ultrasonic propagation. The ultrasonic detecting results are verified by testing the pieces with defects.

Key words: aramid paper honeycomb, through-transmission ultrasonic, pulse echo ultrasonic, X-CT, honeycomb collapse, honeycomb cell bubblinghttp