Mechanical properties of PEK-C interlayer toughened carbon fiber/epoxy composites

The thermoplastic resin polyaryletherketone with cardo (PEK-C) films of three different thicknesses (about 1 μm, 10 μm, 30 μm) were prepared by dip-coating method. Hot pressing technology was employed to obtain the film interleaved carbon fiber/epoxy composite laminates. The mode I interlaminar fracture toughness (G_IC), compressive after impact (CAI), interlaminar shear strength and flexural properties were tested to investigate the effect of PEK-C film and film thickness on the mechanical properties of carbon fiber/epoxy composites. The microstructure was observed by SEM and the phase structure was scanned by AFM. The results show that G_IC, CAI and interlaminar shear strength increase for the carbon fiber/epoxy composite laminates with PEK-C films of different thickness. G_IC and shear strength are increased maximally at a film thickness of 10 μm, which are increased by 157.17% and 17.57%, respectively. CAI is the largest at a film thickness of 30 μm, reaching 186.67 MPa due to the fact that PEK-C and epoxy resin form a dual-phase structure during the hot pressing curing process, improving the toughness of the material. The flexural strength and flexural modulus of carbon fiber/epoxy composite laminates decrease with the increase of the film thickness, from 1 551 MPa, 106 GPa without films to 965 MPa, 79 GPa at the film thickness of 30 μm due to the diffusion of PEK-C resin into the epoxy resin, which reduces the fiber volume fraction and material stiffness.