Evaluation non destructive par thermographie pulsee: Quantification de la corrosion feuilletante (French text).

摘要

The exfoliation is more likely to affect high resistant alloys like aluminium 7075-T6 than other materials. This is caused by heat treatment of the alloy, which brings the alloy at a high level of energy. The corrosion occurs because the alloy tends to reach a level of energy that is more stable. The object of this thesis is the quantification of the exfoliation on aluminium 7075-T6 specimens by pulsed thermography. The quantification of this type of corrosion is important since it allows to know how badly are affected the inspected structures. Since aluminium has a poor emissivity, this thesis also tries to find a new coating to replace the black paint, which is usually used by the industry. The proposed technique is not as good as black paint but takes less time to apply. Finding a new coating and using the same way to apply the coating can improve the proposed system. The quantification of the exfoliation by pulsed thermography is problematic, because it is located near the surface and the thermal waves reach it very soon after the excitation. With black paint, at the time the waves reached the exfoliation, the camera is still in a saturation state. Because of the saturation of the camera, the theory found in the literature cannot be applied to quantify the depth of the exfoliation on a painted specimen. However, the lateral dimensions of the exfoliation can be estimated. Even if we try to delay the signal by using a new coating instead of black paint, we are still not able to quantify the exfoliation depth. This is probably caused by the complexity of the exfoliation corrosion that is characterized by multiple air layers.