Inducing in Situ Delamination Monitoring With Enhanced Fracture Toughness in Fiber‐Metal Laminates Using Carbon Nanotubes

ABSTRACT Timely and accurate sensing of delamination/damage and improving the fracture toughness of fiber metal laminates (FMLs) is important to ensure their structural integrity in advanced applications. Here, we demonstrate an efficient strategy to simultaneously improve the fracture toughness and induce in situ damage sensing capabilities in FMLs using carbon nanotubes (CNTs). Experimental results show that CNT addition improves the flexural modulus (19%), mode‐I (36%), and mode‐II (64%) fracture toughness of FMLs. Fractography analysis reveals additional fracture mechanisms after CNT dispersion in conventional FMLs. Higher roughness of the composite layer, CNT pullout, and formation of epoxy cusp are primarily responsible for enhanced fracture toughness in FMLC. In addition, the CNTs form a conducting path within the epoxy and improve the electrical conductivity of FMLs by 3–4 orders of magnitude. This enables in situ delamination/damage sensing in FMLC by monitoring the relative change in their electrical resistance (% R ). The variation in % R is able to capture damage accumulation as well as stable and unstable growth of delamination cracks. Thus, CNT modification offers dual advantages of improving the fracture properties and inducing in situ damage sensing capability in conventional FMLs.