Quantitative analysis of interlaminar toughening of carbon fiber composites molded by CNT film electrothermal in-situ curing

The carbon nanotube (CNT) film electrothermal in-situ curing method utilizes the Joule heating of embedded CNT films to heat and cure carbon fiber composites, offering an efficient and low-cost manufacturing approach. However, introducing the CNT film and applying electric current may influence the interlaminar properties of composites. In this study, the interlaminar properties and toughening mechanism of CNT film electrothermal in-situ curing were quantitatively investigated by comparison with conventional oven curing. The results show that the electrothermally cured composite achieves a 68.33% increase in interlaminar fracture toughness relative to the oven cured composite. A deeper examination reveals that this enhancement arises from the following mechanisms: (1) electrothermal curing strengthens the CNT film-resin interfacial bonding, which increases crack propagation resistance in the CNT film layer and thereby raises the energy required for fracture at the main interface; (2) the strengthened interface induces more extensive fiber bridging, accompanied by film fragmentation and pull-out, thereby further increasing energy dissipation during crack propagation; (3) higher stress concentration at the crack tip within the CNT film layer induces secondary cracks in the plastic deformation zone, transforming crack propagation mode from single main crack growth to synergistic main-secondary crack propagation, thereby further enhancing fracture toughness. Based on the energy dissipation theory in fracture mechanics, the energy dissipation contributions of the main crack (mechanisms 1-2) and secondary crack (mechanism 3) were approximately evaluated as 85.18% and 14.82% of the total fracture toughness, respectively. These findings provide theoretical support for regulating the interlaminar performance of electrothermal cured composites.