Interlaminar toughening of unidirectional CFRP with multilayers graphene and MWCNTs for Mode Ⅱ fracture

Carbon fiber reinforced polymers (CFRPs) often encounter impact load especially for flight vehicles. The invisible delamination raised by the impact leads to largely decreasing on the residual load capacity. The shear stress and delamination of the out-plane play the important role in the impact loading. Therefore, this paper focuses on enhancing the interlaminar shear fracture toughness through adding nano-fillers of multi-walled carbon nanotubes (MWCNTs) and multilayers graphene (mG) between the layers of CFRPs. MWCNT and mG nano-materials are respectively sprayed onto the surface of prepregs at density of 1.0 g/m². The end notched flexure (ENF) testing is carried out for verifying the interlaminar toughening performance. MWCNT toughening strategy with 1.0 g/m² harvests 154.47% improvement on G_IIC (Mode II shear fracture toughness) with medium standard deviation. Multilayers graphene also obtain 105.80% improvement in spite of large data scatter. Scanning electron microscope (SEM) analysis reveals that MWCNT and mG nano-fillers make the shearing fracture appearance roughly in macro-scale, generate more cracks in micro-scale, and improve shear fracture toughness through the crack deflection namely MWCNT pull-out, mG surface peeling and shear debonding.