The effect of carbon nanotubes on the fracture toughness and fatigue performance of a thermosetting epoxy polymer

Abstract

Multi-walled carbon nanotubes, with a typical length of 140 lm and a diameter of 120 nm, have been used to modify an anhydride-cured epoxy polymer. The modulus, fracture energy and the fatigue performance of the modified polymers have been investigated. Microscopy showed that these long nanotubes were agglomerated, and that increasing the nanotube content increased the severity of the agglomeration. The addition of nanotubes increased the modulus of the epoxy, but the glass transition temperature was unaffected. The measured fracture energy was also increased, from 133 to 223 J/m 2 with the addition of 0.5 wt% of nanotubes. The addition of the carbon nanotubes also resulted in an increase in the fatigue performance. The threshold strain-energy release-rate, G th , increased from 24 J/m 2 for the unmodified material to 73 J/m 2 for the epoxy with 0.5 wt% of nanotubes. Electron microscopy of the fracture surfaces showed clear evidence of nanotube debonding and pull-out, plus void growth around the nanotubes, in both the fracture and fatigue tests. The modelling study showed that the modified Halpin-Tsai equation can fit very well with the measured values of the Young's modulus, when the orientation and agglomeration of the nanotubes are considered. The fracture energy of the nanotube-modified epoxies was predicted, by considering the contributions of the toughening mechanisms of nanotube debonding, nanotube pull-out and plastic void growth of the epoxy. This indicated that debonding and pull-out contribute to the toughening effect, but the contribution of void growth is not significant. There was excellent agreement between the predictions and the experimental results.

Multiscale Characterization of Nanoengineered Fiber-Reinforced Composites: Effect of Carbon Nanotubes on the Out-of-Plane Mechanical Behavior

“…A clear reduction in the KIC with the incorporation of CNTs was obtained, contrary to other studies [9,11,26]. An analysis of the fracture surfaces, as summarized in Figure 1, indicates a smooth fracture surface for the neat resin (a) and a rougher surface of the CNT reinforced resins, as shown in (b).…”

“…The reduced moduli, obtained by nanoindentation and the results of the tensile and shear tests, show no significant changes (less than 3% of variation) with CNT incorporation. Despite the fact that several articles [6][7][8][9][10][11]26] indicated an enhancement of the mechanical properties of polymeric resins by the incorporation of CNTs, it should be noted that the epoxy resin used in this work has a high stiffness compared to other related research studies. This is in agreement with previous studies by Ci and Bai [6] who concluded that the resin stiffness decreases the potential positive effect of CNTs.…”

Graphene nanoplatelet-modified epoxy: effect of aspect ratio and surface functionality on mechanical properties and toughening mechanisms

“…For both the HalpinTsai and Mori-Tanaka models, the aspect ratio is the factor that has the most significant effect on the composite modulus predicted. The models can be modified to take into account the reduction in aspect ratio [53], however the introduction of such constants tend to be strictly systematic and changes depending on the system used. The Halpin-Tsai and Mori-Tanaka "parallel" models were relatively close in value, however there were more deviations in the "random" arrangement as the concentration is increased.…”

“…The measured values of G i ranged from 4 to 70 J/m 2 , comparable to other fibre reinforced polymers. For the current study, a value of G i = 25 J/m 2 was used [53]. For the platelet pull-out mechanism:…”

Fluoride determination in carbon nanotubes by ion selective electrode

“…[1][2][3][4][5] The properties of CNTs could be chemically modified by addition of halogens, as fluorine. [6][7][8][9] Some authors have reported that the functionalization of CNTs with fluorine significantly changes their electrical, mechanical and optical properties.…”