Predictions of Energy Absorption of Aligned Carbon Nanotube/Epoxy Composites

The potential of aligned CNT/epoxy nanocomposites towards energy absorption applications was demonstrated using finite element modeling. For that, two cases studies were carried out: (1) prediction of crack resistance characteristics of epoxy reinforced with aligned double-walled CNTs (DWCNTs), and (2) prediction of rate-dependent compressive response of epoxy filled with aligned single-walled CNTs (SWCNTs). It was found that reinforcing epoxy with CNTs can significantly reduce the crack driving force in epoxy and increase strains to failure as a result of the damage propagation at the CNT–epoxy interphase. Particularly, enhancements of shear stiffness, shear strength and mode II fracture energy of CNT–epoxy interphases via CNT functionalization and minor increases of low sp³-bond densities in the interwall phase of DWCNTs were shown to increase the crack resistance of the nanocomposite. Furthermore, it was found that the linear and nonlinear compressive deformations and thus the energy absorption characteristics of epoxies can be significantly affected by the presence of CNTs. Specifically, the initial stiffness was increased and the post-yield behaviour of the nanocomposite showed enhanced strain stiffening, both with increasing CNT loading and increasing CNT aspect ratio. Additionally, a combined effect of aspect ratio and volume fraction on energy absorption characteristics was found. This suggests that the average aspect ratio of CNTs should be carefully selected in order to maximise the energy absorption for the given CNT volume fraction.