Noninvasive in Situ Monitoring for Compound Material Production Using Low Cost Foil Sensors

Robust qualities make composite materials extremely valuable for the aerospace industry. However, some issues using these materials become apparent during production. Structures made from composite materials are still primarily produced manually, which often leads to increased variability in the quality of the final products. This study demonstrates that simple and self-manufactured low-cost foil sensors can be employed to monitor the curing process of potting materials, particularly synthetic resins, during the production of composite structures for aerospace vehicles. In the method used here, the sensors remain attached to the structures so that they can potentially be used for monitoring later when in flight and under load. For this study, custom sensors were produced in-house using an economical method. These sensors were designed as interdigital electrodes and were coated with conductive ink onto a polyimide substrate. Interdigital sensors were used as their application requires only one-sided access to the monitored structure. The foil sensor was implemented and assessed using a model aircraft wing segment as an illustrative example. In this context, the foil sensor served as a measurement probe for capturing time-series impedance spectra. The results demonstrated the foil sensor's mechanical and chemical durability during the test preparation and execution phases on the model, alongside its electrical suitability for this intended purpose. The collected measurement curves underscore this method's efficacy for monitoring composite materials' curing process during production.