Mixed-mode I/II interlaminar fracture toughness of carbon fiber/epoxy composites with the addition of multiwalled carbon nanotubes by spraying technique

This work reports the effect of multiwalled carbon nanotubes on mixed-mode I/II interlaminar fracture toughness (G(I/IIC)) of unidirectional carbon fiber/epoxy composite laminates made by prepregs. The carbon fiber/epoxy laminates were fabricated in an autoclave with a previous deposition of different multiwalled carbon nanotube contents at their middle plane interface by spraying technique. Mixed-mode bending tests were conducted on carbon fiber/epoxy laminate specimens under different mixed-mode ratios. The results of mixed-mode bending tests showed that the addition of multiwalled carbon nanotubes can effectively improve the G(I/IIC) of carbon fiber/epoxy laminates. With a 0.2 wt.% multiwalled carbon nanotubes content in carbon fiber/epoxy laminates, the G(I/IIC) under mixed-mode ratios of 0.2, 0.5 and 0.8 increased by 25%, 12% and 19%, respectively. These results were explained in terms of the damage mechanisms observed at the fracture surfaces of tested specimens by scanning electron microscopy.