Investigation into the toughening mechanism of epoxy reinforced with multi-wall carbon nanotubes

This study reports the reinforcement and fracture toughening mechanism of pristine multi-walled carbon nanotubes (MWCNTs) on epoxy matrix. The tensile strength and fracture energy (GIC) of the epoxy polymer increased simultaneously upon the addition of a small amount of MWCNTs. The fracture surfaces of single-edge-notch three-point bending test specimens were analysed by scanning electron microscopy, and the double-notch four-point bending technique was used to investigate the fracture process by transmission electron microscopy, respectively. MWCNT pull-out and subsequent plastic void growth were found; meanwhile, fracture of MWCNTs was observed along the crack propagation path. The theoretical model of shearing band initiated by the stress concentrations around the MWCNTs is the dominant toughening mechanism. While the crack bridging of MWCNTs and the plastic void growth of epoxy also have a toughening effect.