An experimental study of interlaminar shear fracture toughness of a nanotube reinforced composite

This study demonstrated that fluorine functionalized carbon nanotubes (f-CNTs) can be used to reinforce in the midplane of a fiber reinforced epoxy composite laminate for increasing the interlaminar shear fracture toughness. A spraying methodology was used to deposit the f-CNTs on the midplane carbon fabric to produce this through-thickness interlaminar reinforcement. The four-point end notch flexure (4ENF) specimen was used in the experiments to calculate the critical strain energy release rate, GIIc, to quantify a value for fracture toughness. Compared to the neat case (0.0 wt% CNTs) there was a 23% increase in the average initiation and 27% increase in the average propagation GIIc with only 0.5 wt% f-CNTs dispersed on the fabric and in the resin of the midplane region. High resolution microscopic examinations of the specimen fracture surfaces suggest that the functionalized carbon nanotubes are covalent bonding nanoscale tethers between the fibers and the epoxy resin, resulting in toughened fiber–matrix interfacial strengths to achieve these improved through-thickness mechanical properties for this nanocomposite laminate system. This nanotube technology could displace the need for using cross-fabric stitching or pinning, or using thickening interleaf layers at the midplane region of laminates in order to improve the interlaminar shear fracture toughness.