Detecting Defects in Composites Using Combined Heating/Cooling: Theory and Experiments

A novel active thermal nondestructive testing (TNDT) technique using sequential heating and cooling is proposed. Properly chosen parameters of a heating/cooling technique may result in a sample excess temperature that is close to the sample’s initial temperature, which causes zero excess temperature when hidden defects still produce noticeable temperature signals. In this case, the running temperature contrast may increase, which improves detection reliability. This is due to the fact that the effect of emissivity variations on the surface of a test sample are minimized if the sample temperature is close to the ambient temperature.