Simultaneously improving mode I and mode II fracture toughness of the carbon fiber/epoxy composite laminates via interleaved with uniformly aligned PES fiber webs

In this work, a uniformly aligned polyethersulfone (PES) fiber web was designed and fabricated by the melt-spinning PES yams. Such fiber web was adopted as an interleave to simultaneously improve both mode I and mode II fracture toughness of the carbon fiber/epoxy composite, addressing the issue of transforming the thermoplastic component into a well-controlled uniform and ordered phase structure without being influenced by the liquid forming process. The dissolution behaviors of the PES filaments in the epoxy resin were studied by the optical microscopy with a hot stage. The results indicated that the PES filaments were not dissolvable at the temperature of the resin infusion process, but could be dissolved during the curing process of the epoxy resin in a well controllable way and period. Both the mode I and mode II interlaminar fracture toughness of the composites were investigated as a function of areal densities of the PES fiber webs (7.3,14.7, 21.2 and 28.3 gsm) carefully. A maximum enhancement up to 120% and 68.8% on mode I and II fracture toughness, respectively was obtained with the introduction of the 28.3 gsm-PES fiber web compared to the laminates without interleaves. Analysis of the fracture surfaces of the laminates elucidated that the distinctive improvement of the interlaminar fracture toughness could be attributed to the characteristic interlaminar structures induced from the phase separation of PES in epoxy resin. Moreover, the interleaved laminates displayed an increase of 18.2% and 43.8% for the interlaminar shear strength (ILLS) and compression-after-impact (CAI) properties, respectably. The tensile and flexural properties of the composite were thereafter explored which indicated slightly enhancement on the strengths.