Investigation of the spring-in phenomenon of carbon nanofiber reinforced glass fiber/polyester composites during vacuum assisted resin transfer molding

Process-induced residual stress arises in polymer composites as a result of resin shrinkage during the cure cycle. When a shell-like composite part is de-molded, the residual stress results in the change of dimensions such as the spring-in phenomenon, in which the enclosed angle of a curved composite part becomes smaller than its original modeled angle due to the process-induced residual stress. To have good precision in such composite parts, the dimensional instability of the enclosed angles must be controlled and/or compensated. In this research, 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, hence, may be useful in improving the dimensional stability of polymer composites. This thesis presents an integrated experimental and numerical research on the effect of CNF on the dimensional stability of the composite parts manufactured using VARTM. The experimental results showed that by adding CNF into the polyester resin, the spring-in angles of the L-shaped composite parts were considerably restrained and the FEA simulation results showed good agreement when compared with experimental results, which validated that the FEA model is able to determine the spring-in angles with an acceptable range of deviation.