Improving energy dissipation and damage resistance of CFRP laminates using alumina nanoparticles

In this paper, the effect of a toughened epoxy matrix on the damage evolution, energy dissipation, and permanent indentation of composite laminates under out-of-plane (transverse) loading is presented experimentally. The epoxy matrix was toughened by 3% alumina nanoparticles with sizes less than 200 nm. A quasi-static indentation test was exploited to characterise the damage modes and evaluate the dissipation of energy of the composite laminate. The dissipated energy was evaluated as the enclosed area between the loading and unloading curves, while the damage resistance was expressed as the number of delaminations and their size. The results showed that epoxy toughened by alumina nanoparticles, showed an improvement in the damage threshold load by 27.3% and higher ultimate load under indentation. Regarding the damage resistance, the toughened laminates showed lower number of delaminated interfaces and lower projected delamination area than untoughened laminates. This is due to the localised damage under the indenter, the matrix cracks at low indentation energy and fibre breakages occur at high indentation energy.