Theoretical understanding of fracture toughness improvement in carbon nanotube-coated fiber/epoxy composites: A multiscale study

Abstract

In this study, the mechanisms underlying fracture toughness improvement in carbon nanotube (CNT)-coated fiber/epoxy composites were investigated using multiscale analysis. To capture the macroscopic toughening mechanisms (such as crack path deflection induced by the fiber), a phase field fracture simulation was employed. A multiscale fracture model incorporated microscopic toughening mechanisms (including interfacial debonding, subsequent plastic nano-void growth, and pull-out of the nanotubes) during macroscopic crack propagation. Results indicate that at the mesoscale, the energy dissipation increases with CNT volume fraction, emphasizing the critical role of CNT modification in enhancing fracture toughness. Furthermore, the CNT coating layer, characterized by a high CNT volume fraction, facilitated significant energy dissipation, further enhancing the overall fracture toughness of the CNT-fiber/epoxy composites. In conclusion, macroscopic cracks frequently propagate across the coating layer, contributing to significant energy dissipation during crack propagation.