Modelling of the carbon nanotube bridging effect on the toughening of polymers and experimental verification

The effect of aligned and randomly oriented carbon nanotube (CNT), with respect to the crack growth plane, on the fracture toughness of polymers is modelled in this paper using the Elastic Plastic Fracture Mechanics. According to a critical length, two dominant toughening mechanisms for CNT-modified polymers are presented, i.e. CNT pull-out and CNT rupture. The model is then used to identify the effect of CNTs geometrical and mechanical properties on the enhancement of fracture toughness in CNT-modified polymers. The key CNT properties are the CNT radius, average length, ultimate strength, elongation before failure, interfacial shear strength between CNTs and the polymer and nanotube volume fraction. Finally, experimental results are compared with the model predictions. The correlation shows that processing of long, aligned CNTs remains the main barrier in achieving major fracture toughness enhancement.