Smart cure cycle for reducing the thermal residual stress of a co-cured E-glass/carbon/epoxy composite structure for a vanadium redox flow battery

Abstract

The vanadium redox flow battery (VRFB) is considered as one of the most promising energy storage system in the future. It is composed of two endplates and a stack which consists of flow frame (FF), electrode, bipolar plate (BP) and membrane. Because the electrolytes flowing in the stack are sulfuric-acid-based solutions, prevention of leakage is important. The unified structure of the FF and the BP manufactured by co-curing E-glass/epoxy and carbon/epoxy composites not only prevents leakage, but also simplifies assembling process. However, large thermal residual stress is induced due to the difference of coefficients of thermal expansion between E-glass/epoxy and carbon/epoxy composites. In this work, smart cure cycle was developed to reduce the thermal residual stress of the co-cured E-glass/carbon/epoxy structure for VRFB. The deformations of structure fabricated using smart cure cycle were investigated with respect to the degree of cure and post-cure process using the viscoelastic properties of composite materials during post-cure process. In addition, the thermal residual stress and actual bonding temperature were calculated. Using the experimental results of degree of cure and actual bonding temperature, a finite element analysis was performed to verify the stress of the co-cured FF BP structure as a function of the cure cycles.