Fracture Mechanisms in Epoxy Composites Reinforced with Carbon Nanotubes

Recent advances in nanotechnology and nanostructured materials offer the possibility to improve the mechanical properties of composite structures in terms of toughness and stiffness. In particular, in aerospace applications research efforts are focused on the design of advanced composite materials reinforced with carbon nanotubes (CNTs) that combine weight saving with multifunctional properties, including thermal, mechanical and electromagnetic ones. It is well known that carbon nanoparticles enhance the fracture strength, the modulus, and the yield strength of a polymer matrix through different mechanisms. However, despite the large amount of investigations on CNT-based composites and their relevant properties, there is a lack of understanding of the mechanisms leading to the failure of these materials under impact or static loads, which limits their use in practical applications. In this work, we present an experimental investigation of the fracture mechanisms of aerospace grade epoxy composites reinforced with multi-walled CNTs bridging the mechanical characterization with non-destructive methods, such as optical spectroscopy and electron microscopy. Our results show that it is possible to link the failure mechanisms of the nanostructured composite at the interface between the CNT and the epoxy matrix, namely cracking, pull-out and telescopic failure, with the molecular fingerprint of the carbon structure at the fracture surface after mechanical testing.