Effect of filler waviness and orientation on the damping behavior of CNF-reinforced epoxy composites

An ever increasing demand for material performance coupled with recent advances in the production and availability of nanoscale materials has led to a significant interest in the use of nanoscale fillers to augment and tailor material performance in nanocomposites. Specifically, the use of high aspect ratio fillers, such as carbon nanotubes and carbon nanofibers (CNF) to augment the viscoelastic performance of nanocomposites has been the focus of many studies. Previous study has shown the use of high aspect ratio fillers to significantly enhance the damping capacity at low frequencies by more than 100 %, relative to the neat epoxy. 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 both the effect of the random filler orientation and the effect of filler waviness in examining the viscoelastic response of CNF-reinforced nanocomposites. Using a fundamental approach, this study employs experimental, analytical, and numerical modeling techniques to characterize the amount of strain energy transferred to the filler and the matrix, and to indirectly estimate the effective loss factor of the filler. Utilizing experimental investigation coupled with parametric inquiries using strain energy methods relative to both filler orientation and waviness, this study provides fundamental insight into the effect of imperfect geometries and random filler distributions seen in nanocomposites utilizing high aspect ratio fillers, such as CNF.