Development of multifunctional composites for aerospace application

Carbon-fiber-reinforced polymer composite structures are widely used in today's aerospace industries. However, the introduction of the composites in mainframes of modern structures presents special challenges and issues regarding their impact damage resistance due to the brittle nature of the matrix resins and the multifunctional properties (e.g., electrical conductivity) because the composite structures are poor conductors of extreme electrical currents generated by a lightning strike.For the technological challenge, the first approach, the so-called ex situ toughening technology in the chapter, is associated with the use of amorphous thermoplastic films as interleaves. When an interleaved composite laminate with a thermosetting matrix is cured, highly toughened thin interlaminar regions are established with phase separation and phase inversion. The technology is further developed to meet the challenge of cost-effective liquid moulding by developing preform-based fabrics, the so-called ES™-Fabrics. Improved interlaminar fracture toughnesses, compression after impact (CAI) strength, and balanced in-plane mechanical properties have been achieved.The second approach is the use of the interleaf material surface coated with conducting silver nanowires (AgNWs). Typical interleaf materials include the thermoplastic films perforated and plastic veils. The AgNWs are deposited on the interleaf surface and even across its thickness; they densely interconnected with each other to form a conductive network like a "spiderweb." In this way, two interdependent network structures coexist at different scales. On the one hand, the film or veil framework at the micron scale is essential for interleaf toughening, with a substantial improvement in interlaminar fracture toughness, G_IC and G_IIC. On the other hand, it provides a mechanism for adding nanoscale AgNWs. By incorporating the interleaf materials into the laminated composite system, a nanoscale, 3D cross-linked AgNW network is established throughout the whole composite, providing a clear improvement in electrical conductivity in the transverse and thickness directions of the carbon-fiber composites. The technology is thus called functionalized interlayer technology (FIT). The key advantage of such a technique is that it can significantly and simultaneously increase the impact damage resistance and electrical conductivity of structural composites by selectively interleaving the functionalized interleaf materials.