Carbon Fiber Composite Chassis Components, Opportunities and Challenges

Abstract

Using lightweight components to reduce vehicle mass is one of the tactics available to vehicle manufacturers to reduce CO2 emissions. Carbon fibre reinforced polymer composite with its high strength to density ratio is one of the potential materials to reduce component mass. The lessons learned from three research and development projects on automotive chassis structural components designed, manufactured and tested using carbon fibre composites provides insights into the opportunities for mass reduction and the cost, manufacturing and analysis challenges that combine to limit the applicability of carbon fibre composites in high volume automotive use. Projects investigated three structural cassis components, the Focus rear suspension tie blade knuckle, the F-150 front suspension lower control arm, and the Fusion (Mondeo) front subframe. All the projects developed, analysed, manufactured and tested carbon fibre composite replacement components that fit the package and met equivalent performance requirements to the production parts. Then the designs and manufacturing plans informed the cost estimates for these components at high automotive volumes. The tie blade knuckle chose thermoplastic resin while the front lower control arm and subframe investigated thermoset resin carbon fibre composites. Carbon fibre reinforced polymer composites offer the opportunity of approximately a 30% mass reduction compared to a steel component. This mass savings is less than anticipated. Due to the high constituent material costs of both the carbon fibre and the high performance resin, the complex manufacturing processes, and the final assembly processes the resultant "weight buy" exceeds an additional $35 USD of variable cost per kilogram of mass saved compared to the production steel component. All three of the components investigated require multi material solutions that include both random chopped and oriented continuous carbon fibre composites plus steel reinforcements at high point load areas such as the bolted connections. Also, the predictive CAE tools are not yet fully mature for carbon fibre composites leading to lower confidence initial designs.