Characterisation of inclusions and disbonds in honeycomb composites using non-contact non-destructive testing techniques

Honeycomb composite structures are increasingly being used in the aviation and aerospace industries. For convenient quality evaluation of such advanced composites, several kinds of non-contact non-destructive testing techniques are widely used and are proving to be promising tools for the integrity assessment of honeycomb composites. In this study, the detection performance of air-coupled ultrasonic pulse compression C-scan, lock-in thermography and X-ray digital radiography methods for the characterisation of typical defects in honeycomb composite structures is analysed. For this purpose, three honeycomb composite samples with simulated inclusions or disbonds are prepared and experiments are conducted using the different methods. The contrast-to-noise ratio (CNR) is used to evaluate the image quality and a typical threshold method is used to determine the minimum detectable defect size using the specific testing method. In addition, the features of the different methods are summarised. Finally, the advantages and limitations of the three non-contact non-destructive testing techniques for the evaluation of honeycomb composites are discussed based on the experimental results and basic conclusions are also drawn for the preferred approach in inspecting for particular defect types.