Process induced residual stress arises in polymer composites as a result of resin shrinkage during cure cycle. When a shell-like composite part is demolded, these residual stresses result in change of dimensions such as spring-in, which is a phenomenon that the enclosed angles of the composite part are reduced due to process-induced residual stress. To have good precision in the composite part, the dimensional instability of enclosed angles must be controlled and/or compensated. The traditional approach is to estimate the spring-in and consequently correct the mold geometry to counterbalance the predicted dimensional instability. The success of such mold design practice relies on the past experience or by costly trial and error approach. In this paper, we present a new approach to reduce the spring-in by using Carbon Nanofibers (CNF). CNF have remarkable physical and mechanical properties and have excellent dimensional stability and hence may be useful in improving the dimensional stability of polymer composites. In this experimental study, we dispersed different fractions of CNF into fiberglass/polyester composite parts with corner angles and compared their spring-in angles after the composite parts were demolded. The results show that the CNF can effectively restrain the undesired deformation and improve the dimensional stability of polymer composites during manufacturing process.
Plasma coating of carbon nanofibers for enhanced dispersion and interfacial bonding in polymer composites