Detecting an anomaly

The use of composite materials is constantly increasing in the aeronautical, space and defense fields (airplanes, helicopters, engines, missiles...) because of their high stiffness and specificity which allow to realize lighter and more efficient structures, a great flexibility in the design, and a high fatigue resistance.

How to ensure the health control of these composite structures? There is a risk of impact during transport or during assembly. It is possible to detect possible damage by ultrasound, but this phase is very long, about two hours per square meter.

In collaboration with the Airbus group, we are developing piezochrome coatings whose optical properties change according to the pressure. The objective is to develop a paint capable of identifying with the naked eye any impact above a given threshold. If necessary, the detection of damage is associated with a change in color and/or the emission of a luminescence signal.

The objective is to create a first level of monitoring from the piezochromic properties, allowing a controller to quickly detect a suspicious impact. Ultrasonic inspection would then be limited to only those areas that are useful and likely to be damaged, thus saving considerable time.

The increasing use of composite materials makes it necessary to track down the accidental occurrence of an abnormal rise in temperature. In this context, our teams have developed heat-sensitive coatings capable of detecting a localized overheating condition on a part close to hot areas, such as an engine hood.

The aim is to improve safety and to quickly identify an incident, such as a hot air leak, in order to anticipate a maintenance action.

For Sophie Senani (former Research Engineer in surface treatment at the Airbus Research Center), "Heat-sensitive technology has been around for a long time, but the chemistry developed by OliKrom provides greater precision of the temperature transition threshold and more resistant performance in terms of longevity, which is essential in aeronautics."

One of the challenges of this development was to develop a thermochromic paint with two irreversible detection thresholds. Molecular engineering programming of the materials made it possible to adjust the first irreversible color change to 120°C and the second to 140°C.

A validation plan was then successfully carried out, enabling the technology to be deployed in real flight conditions on an A320 plane.