A comparison between thermosonics and thermography for delamination detection in polymer matrix laminates

Over recent decades, industry has used more and more frequently composite laminates. If many Non-Destructive Testing (NDT) methods have already been developed to test such structures, detecting defects in polymer matrix laminates remains difficult. After a short overview of the main existing NDT methods, this paper focuses on two techniques which appear to be very promising: thermosonics and infra-red (IR) thermography. For thermosonics tests, an ultrasonic horn mechanically loads the sample, while an IR camera records the defect heating. For thermography tests, the heating is due to an optical wave. If minor improvements on the test device are presented for thermosonics tests, IR thermography tests are achieved with a CO₂ laser as excitation source, which is a very innovative approach. This paper provides many experimental results obtained from an aeronautical carbon-epoxy plate with a central delamination. It is shown that both methods are very suitable for detecting such a defect, even if each method has its own advantages. Finally, some improvements to further optimize the thermography tests are proposed in conclusion.