Study on Interlaminar Fracture Toughness of Carbon Fiber/Epoxy Composites Toughened With Polyethersulfone/Carbon Nanotubes/Nano‐Alumina Films

ABSTRACT To improve the interlaminar fracture toughness of carbon fiber reinforced polymer (CFRP) composites, a polyethersulfone (PES)/carbon nanotubes (CNTs)/nano‐alumina (nano‐Al 2 O 3 ) hybrid membrane was fabricated using the wet phase inversion method. The optimal toughening configuration for thermoplastic resin‐blended particle‐toughened CFRP composites was evaluated through double cantilever beam (DCB) and end‐notched flexural (ENF) tests conducted at ambient temperature and under cyclic thermal loading (35 cycles between room temperature (RT) and −55°C). The results show that CNTs and nano‐Al 2 O 3 markedly increase interlaminar fracture toughness through distinct reinforcement mechanisms. The highest Mode I fracture toughness is achieved at a CNTs/nano‐Al 2 O 3 ratio of 3:2, where G IC‐c increases by 90.84% and G IC‐p increases by 82.47%. The maximum Mode II fracture toughness occurs at a CNTs/nano‐Al 2 O 3 ratio of 2:3, with G IIC enhanced by 164.39%. Thermal cycling reduces the interlaminar properties of CFRP composites; however, its adverse influence is least pronounced for CFRP reinforced with hybrid membranes. SEM observations were further conducted to characterize the microstructure of the reinforced interlaminar interface and to analyze the differentiated synergistic toughening mechanism provided by the hybrid membranes.