Strain dependent visco-elastic response of CNF's reinforced epoxy composites

Recent advances in the production and availability of nanoscale materials has led to a significant interest in the use of nanoscale fillers in order to augment and tailor material performance in nanostructured composites. A specific area of interest is the use of high aspect ratio fillers, such as carbon nanotubes (CNT) and carbon nanofibers (CNF) to augment the damping capacity of nanostructured composites. Previous work has shown the use of high aspect ratio fillers to significantly enhance the damping capacity at low frequency by more than 100%; however, the enhancement achieved has been predicated on strain levels in the composite. Our previous studies have indicated a strong strain dependent response in the nanostructured composites utilizing CNF to augment damping capacity. This is due, in part, to the random distribution of fiber orientations seen in the nanostructured composites. The random distribution of filler orientations is thereby relative to the load applied to the composite that results in a critical shear stress thresholds being surpassed at the nano scale, allowing the filler to slip relative to the matrix, resulting in frictional energy dissipation as heat and thereby inducing damping to the high aspect ratio filler nanostructured composite. In light of the promise this technology holds for use in engineered applications requiring specific damping performance, there remains a fundamental lack in understanding of the precise mechanisms and thereby a lack of ability to accurately predict material performance, which is limiting application of the technology. This study looks at the effect of the random filler orientation of CNF included composites and examines the viscoelastic response of the composite specifically investigating the effect of filler orientation relative to the loading direction and the effect of filler waviness. Furthermore, this study looks at the strain dependent nature of the viscoelastic response and develops an analytical modeling tool to look at the effect of the strain dependent viscoelastic response seen in previous studies with the aim of achieving a better fundamental understanding of the effect of filler orientation and the associated strain dependent nature of the viscoelastic response seen in high aspect ratio nano - filled composites.