Development of Sensing Techniques for Material State Awareness in Natural Fiber Composites

Natural fiber reinforced composites (NFRCs) offer a potential alternative to carbonfiber composites in some aeronautics applications. Active health monitoring may enable broader use of NFRCs by providing the material state awareness needed to reduce design knockdown factors and to monitor for environmental degradation in service. This paper describes initial steps taken toward development of dielectric and acoustic in-situ sensing approaches that would allow moisture and material property changes to be monitored in real-time. Coupons of three different thermoplastic NFRC material systems were exposed to accelerated moisture absorption and changes in properties relative to baseline values were assessed. Strong correlation in both dielectric and acoustic properties with moisture level were observed, with dielectric properties showing reversible, monotonic change, while some acoustic properties changed irreversibly.