Improving the interlaminar toughness of the carbon fiber/epoxy composites via interleaved with polyethersulfone porous films

In this study, a phase inversion approach was employed to fabricate four different thicknesses (20 mu m to 100 mu m) of polyethersulfone (PES) porous films with visible holes (1 hole/cm(2)) on the surface, applied as interleaves to improve the interlaminar fracture toughness of carbon fiber/epoxy composite laminates prepared by vacuum assistant resin infusion process (VARI). The film could dissolve into the epoxy resin which as clearly evident by the optical microscopy under a controlled condition. It was noted that the thickness of the resin-rich layer and the distribution of PES microspheres in the interlaminar layer depended on the thickness of the PES porous film. Also, mode I and mode II fracture toughness, interlaminar shear strength (ILSS), flexural properties as well as tensile properties of the CF/EP composites had all been characterized and analyzed in detail and in order. The results demonstrated that mode I and mode II fracture energies at the optimal interleaved laminates for the toughened system were increased by 61.5% and 55.1% compared to the composites without interleaves, respectively. Besides, PES porous film interleaved laminates displayed an increase of 32% for the interlaminar shear strength and no significant changes in the flexural and tensile properties. It was observed that the films induced toughening via two mechanisms: i) cohesive failure in a thicker resin region and ii) crack deflection and microcrack caused by PES microspheres, illustrated in the microstructure analysis of the failure surfaces and the observations of the crack propagation path.