Interlaminar fracture toughness of composite laminates with CNT-enhanced nonwoven carbon tissue interleave

Abstract A nonwoven carbon tissue (NWCT), composed of conventional carbon fibers, was coated with carbon nanotubes (CNT) to compose a multi-scale reinforcing interleave layer which can be directly incorporated into the composite laminate layup process. This CNT-enhanced NWCT layer was found to significantly improve the Modes I and II interlaminar fracture toughness of a carbon fiber reinforced polymer (CFRP) laminate, as measured by double-cantilever-beam (DCB) and end-notched-flexure (ENF) tests. G IC and G IIC of the CNT-enhanced NWCT specimens were compared with baseline CFRP specimens having no interleave, and also specimens having NWCT interleave with no CNT. The mean G IC of the CNT-enhanced NWCT specimens was measured to be 353% higher than the CFRP specimens, a great improvement over the NWCT specimens which showed a 5% reduction relative to CFRP. The mean G IIC of the CNT-enhanced NWCT specimens was 246% higher than the CFRP specimens, which is a significant improvement over the 194% increase measured for the NWCT specimens. Increased G IIC was mainly achieved via crack bridging provided by the NWCT carbon fiber morphology. Additional improvement in G IIC , and the increase in G IC (rather than decrease) of the CNT-enhanced NWCT specimens was due to local CNT reinforcement of the resin near the NWCT fiber surfaces. Scanning electron microscopy shows evidence of improved resin-to-NWCT interface adhesion, short fiber breakage, and CNT pullout at the fracture surfaces.