An experimental and numerical investigation of highly strong and tough epoxy based nanocomposite by addition of MWCNTs: Tensile and mode I fracture tests

The present study investigates, through experimental and numerical approaches, the incorporation effect of different weight concentrations of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of epoxy. Tensile and mode I fracture tests were performed to investigate the effect of the addition of MWCNTs on Young's modulus, Ultimate Tensile Strength (UTS), critical stress intensity factor (KIC) and critical strain energy release rate (GIC). Different carbon nanotubes (CNTs) contents were employed to compare the effect of the resulting microstructures (well-dispersed and agglomerated CNTs) on the mechanical properties. Field Emission Scanning Electron Microscopy (FESEM) and Scanning Electron Microscopy (SEM) were used for microstructural analysis and fractography. Experimental results showed that UTS was improved (28%) by incorporation of MWCNTs while the KIC and GIC were substantially increased by 192% and 614%, respectively. CNT pullout and crack bridging were the main contributing mechanisms in toughening the epoxy at low CNT contents (0.1 and 0.25 wt%). In contrast, a combination of crack bridging and crack branching was responsible for the resin toughening in the case of 0.5 wt% loading. The significant increase for KIC and GIC demonstrated the excellent performance of the dispersion approach used in this study. Finite Element modelling was used to provide a more robust analysis of the effect of CNT incorporation in tension tests and of the toughening mechanism of the nanocomposites in mode-I fracture tests.