Fracture toughness and failure behavior of CF/epoxy composites interleaved with melt‐infused PET, PEI, and PEEK film

Abstract This study investigates the effect of incorporating polyethylene terephthalate (PET), polyetherimide (PEI), and polyether‐ether‐ketone (PEEK) thermoplastic films in melt form as interlayers to toughen carbon fiber/epoxy composites. The addition of melt‐infused PET, PEI, and PEEK film into carbon fiber/epoxy composite enhanced the mode‐I interlaminar fracture toughness (ILFT) by 60%, 156%, and 284%, respectively. The primary toughening mechanisms found were plastic deformation and mechanical interlocking through fiber bridging, which left fiber imprint traces on the fracture surface. The mode‐II ILFT of PET, PEI, and PEEK film interleaved laminates was improved by 80%, 188%, and 96%, respectively. Plastic deformation was observed to be the principal toughening mechanism. Notably, these enhancements in ILFT were achieved while simultaneously increasing interlaminar shear strength. These findings show the role of hot‐melt‐infused PET, PEI, and PEEK thermoplastic films in the improvement of ILFT of composites which is crucial in the design of damage‐tolerant composite structures. Highlights Composites were interleaved with PET, PEI, and PEEK films via melt‐infusion. Mode‐I and mode‐II ILFT were significantly enhanced, up to 284% for PEEK. Failure exhibited plastic deformation, extensive fiber bridging, and pull‐out. Melt‐infusion created complex, mechanically interlocked interfaces.