Indentation damage detection in thermoplastic composite laminates by using embedded optical fibers

Abstract

In recent years, optical fibers have received attention as sensors for the purpose of in-service health monitoring in composite materials. Advantages of optical fiber sensors over conventional sensing methods are well-known and include resistance to corrosion and fatigue, similarity of their material properties to the reinforcing fibers, small, flexible and lightweight nature, immunity to electromagnetic interference and high response bandwidth. These features enable their embedding into composite structures and access locations where other sensing methods cannot easily probe. This paper evaluates the feasibility of real-time monitoring of indentation damage in composite laminates from indentation loading using the embedded intensity-based optical fiber sensors. An optical fiber sensing system, which relies solely on monitoring light intensity for providing indication of the composite structural health, offers simplicity in design and cost-effectiveness. For this, aramid/polyvinylbutyral (PVB) laminates with embedded optical fibers were fabricated. Three configurations of woven composites were tested, namely aramid/PVB, metal/PVB and aramid/metal/PVB. Several stacking sequences of aramid and metallic woven layers were used for investigations. Initiation of damage and fracture during testing was detected by observation of the intensity) drop of light signal transmitted through optical fiber.