Experimental investigation of the compressive behavior of epoxy nanocomposites reinforced with straight and helical carbon nanotubes

This paper is aimed at an experimental investigation of the effect of straight and helical carbon nanotubes on the compressive behavior of epoxy nanocomposites. The epoxy nanocomposites are fabricated with varying levels of SCNT and HCNT, each with two different fabrication techniques viz. high shear mixing and ultrasonication. In samples made using high shear mixing, the compressive strength is found to actually decrease, due to poor dispersion of the CNTs, resulting in voids and clumps, which can adversely affect the strength. Ultrasonic homogenization is found to better disperse the CNTs within the epoxy resin with nearly a 10-fold decrease in the heterogeneity size. Compression tests conducted on the ultrasonically homogenized CNT-epoxy nanocomposites indicate a modest increase in the compressive strength. The best increase of 5% is obtained with 1% SCNT. On the other hand, the HCNT samples show a higher post-peak residual stress suggesting an improved mode II/III fracture toughness. The high shear mixed samples exhibit a bulging deformation with no clear evidence of shear localization. On the other hand, the ultrasonic homogenization (UH) samples bulge and eventually show a clear localized shear band, likely due to a smaller heterogeneity size. Some samples with relatively poor dispersion exhibit an axial splitting failure and a comparatively low compressive strength. In addition, it is demonstrated that using acetone as a solvent during dispersion can affect the curing kinetics, which results in a nanocomposite with a rubbery consistency with low stiffness and strength, but high deformability.