Carbon nanotube film interlayer toughened carbon fiber reinforced epoxy resin hybrid composites

Carbon nanotube film (CNTF) interlayer toughened carbon fiber (CF) reinforced epoxy resin (EP) hybrid composites were fabricated via resin transfer molding (RTM) processing in this paper. Multi-walled carbon nanotubes were prepared by chemical vapour deposition, and carbon nanobute films were prepared through vacuum filtration. Model I interlaminar fracture toughness G _Ic of laminates and model II interlaminar fracture toughness G _IIc of laminates are used to characterize the fracture toughness of the RTM laminates. Furthermore, the toughening mechanism is discussed through microstructure of the fracture surface combining mechanical properties. The compact degree of the carbon nanotube films was influenced by the ratio of the multi-walled carbon nanotubes, which led to different impregnation of the carbon nanobute films to the epoxy resin. Experimental results indicated that the carbon nanotube films from carbon nanotubes of large aspect ratios exhibited better impregnation effect than those films from carbon nanotubes of small aspect ratios. The carbon nanotube films intercalated in the interlayer of the composites between the carbon fiber and the matrix resin as a whole laminated structure, and they still kept a continuous grid structure in the CNTF/CF/EP hybrid composites. As to the model I interlaminar fracture toughness G _Ic of laminates, the carbon nanotube films have no obvious improvement on the G_Ic value. However, the carbon nanotube films laid between the carbon fiber layers changed the failure mode of the CF/EP composites, leading to increased initial failure load and breaking load. As to model II interlaminar fracture toughness G_IIc of laminates, experimental results exhibited that the reinforcing efficacy on the sliding mode shear failure was remarkably increased for the CNTF/CF/EP hybrid composites. Model II interlaminar fracture toughness G_IIc of laminates has increased from 1292 J/m² of the CF/EP to 2869 J/m² of the CNTF/CF/EP hybrid composites. There is 120% amplification in G_IIc testing value. Microstructures of the CF/EP composites and the CNTF/CF/EP hybrid composites were characterized through scanning electron microscope (SEM) for understanding the prominent improvement on the toughening properties. SEM pictures showed that there was strong shear history of the carbon nanotube films via the sliding mode failure. The carbon nanotubes absorbed a great deal of energy through shear sliding and hindered crack growth, leading to increase of the G_IIc value outstandingly.