Development of the light weight carbon composite tie bar

Abstract

Stacks of energy conversion systems, such as proton exchange membrane fuel cells (PEMFCs), are composed of several hundreds of components, and they are compacted with tie bars to decrease electrical contact resistance and prevent the leakage of fuels. Since the sealing performance deteriorates over long operation times due to creep deformation of the stack, it is important to maintain a consistent clamping force under the creep deformation of the stack for long-term reliability. In this work, a light weight carbon composite tie bar was developed to replace the conventional steel tie bar. This new composite tie bar can achieve high elastic strain and provides a consistent compaction pressure to the stack over long operation time. To form the complex thread shape of the tie bar without compromising its tensile strength, different types of material were adopted for the thread and rod parts. A carbon fiber mat was used for the thread part because it has a higher drapability compared to other types of carbon fiber, such as unidirectional (UD) or the fabric type. The UD and fabric were adopted for the rod part for their high strength and elongation. Based on the tension test of the fabricated tie bar specimens, an optimum configuration of the carbon composite tie bar has been suggested.