Applications of thermography and ultrasonics for detection of debonding in carbon fibre reinforced composite panels

Carbon fibre reinforced plastic (CFRP) composites are widely employed in modern aerospace structures. Due to the involved and lengthy manufacturing processes, several types of defects can occur during production. There are various non-destructive testing (NDT) methods used to identify defects within composite components. In this paper, the performances of pulse phase thermography and the ultrasonic C-scan methods were used to assess the integrity of a bonded panel with a contaminated bond line. The pulse phase thermography method is a ‘dry’ and quick approach whereas the ultrasonic C-scan method is usually a ‘wet’ and slow approach. The two CFRP assemblies that were used were made by bonding together two sets of panels with paste and film adhesive. This was done in order to assess the performance of the two NDT methods for each of the adhesive bonding techniques. Artificial defects were introduced into the panels using different contaminants including, a release agent, release film, pre-cured adhesive and barrier cream. Both transmission and reflection techniques were employed in the experimental tests using the pulse phase thermography method, whereas only the transmission technique was used for the ultrasonic C-scan method. The pulse phase thermography method has been observed to be highly effective for detecting insertion-type defects. However, from the results of this experiment it was shown that pulse phase thermography is less sensitive to defects as a result of contamination similar to those used in this trial.