Fossil fuel remains the predominant energy source for the transportation sector around the world [1]. Ever stricter global emissions laws as well as increasing consumer awareness to sustainability and the environmental impact of vehicle emissions [2] has driven the advancement of alternative energy sources for vehicles, with electric vehicles (EVs) being at the forefront of this movement. Solar electric cars represent an advancement over regular EVs, utilising photovoltaic cells to generate electricity from solar irradiance. This electricity is used to charge the vehicle’s battery, providing a supplementary source of energy. Current work on solar cars is largely focused on racing and technology development applications [3]. Due to the relative inefficiency of current solar panel technology as a means of energy conversion [4], it is critical to find efficiency gains in other areas of the solar car. A primary method for this is weight reduction, as a lower mass vehicle requires less energy to move. Fibre-reinforced plastics are already well-known for their applications in the automotive industry, primarily due to their superior strength – weight ratio when compared with traditional materials such as steel and aluminium [5–8]. There has been a major shift towards using fibre reinforced composites in solar car components in recent years all over the world [9–11]. As wheels have an additional inertia component (rotational) when compared with other parts of the car, they are a key area for optimisation. Weight reduction of wheels not only offers decreased energy consumption, but also improved suspension response and vehicle handling characteristics.
Czypionka and Kienhöfer [12] developed and validated an FE model of a composite car wheel using ANSYS ACP. A prototype wheel was manufactured, and a dynamic cornering fatigue test was conducted. This test applied the static equivalent of a cornering-induced bending load to the wheel, with strain gauges used to measure the resulting deflection. The authors found a good correlation between FEA results and the physical testing, validating their model. Following final layup optimization, the authors achieved a theoretical weight reduction of 18% over an identical aluminium wheel. Wang et al. [13] conducted a detailed design optimization and analysis of a hybrid wheel using a CFRP rim and aluminium disc. A multi-objective optimization algorithm was employed to optimize layup thickness, sequence, and angle. A prototype wheel was constructed and physically validated using a radial fatigue test and a 13o impact test. Importantly, the optimization scheme reduced the Tsai-Wu failure indices by between 14.4 and 25.8% compared with the initial layup, clearly highlighting the benefits of the optimization process. Research into composite wheels in the aerospace industry has also been conducted. Wacker et al. [14] developed a wheel concept for the nose wheel on an Airbus A320 aircraft. Whilst other studies have focused on developing a wheel with minimal components, in this study the authors use four composite pieces manufactured using hand layup of prepreg fabrics to create a wheel that can be disassembled for ease of maintenance. To accomplish this, the authors designed and physically validated a bolted joint that was used to connect the parts of the wheel. Overall, a theoretical weight reduction of 27% was achieved, however, no physical prototype was constructed. Rondina et al. [15] investigated the automated manufacturing of composite wheels using high-pressure resin transfer moulding (HP RTM). The authors found a reduction in manufacturing time compared with an autoclave method and validated the mechanical performance of the HP RTM material system.
Composite wheels are also becoming commercially available on passenger vehicles. The first company to market with such as wheel was Koenigsegg [16]. Their patented ‘Aircore’ technology uses hollow spokes to achieve a 5kg weight reduction per wheel compared with the standard aluminium wheel. Additionally, Australian-based Carbon Revolution [17] designed and produced a carbon fibre wheel using resin transfer moulding that is used by global vehicle manufacturers including Ford, Ferrari and Renault. Likely due to the proprietary technology used, there is limited technical details available about either the Koenigsegg or Carbon Revolution wheels. Porsche [18] also developed a carbon fibre wheel for the 911 Turbo model. This wheel utilized a combination of hand layup and radial braiding to create a preform that was later impregnated with resin and cured. The finished wheel achieved a weight reduction of 2.15kg per wheel over the standard forged aluminium wheel and 20% higher rigidity at the time of cracking. However, at a price of $17,600USD per set [19] these wheels are significantly more expensive than steel or aluminium wheels.
Manufacturing of current commercially available carbon fibre wheels is labour intensive, contributing to their high price. For example, Koenigsegg relies on hand layup of prepreg fabrics to construct their wheels [20]. Efforts have been made to automate the production of composite wheels. In particular, Carbon Revolution use automated manufacturing processes to create dry fibre preforms that are subsequently placed in a mould and impregnated with resin in an injection process [21]. An alternative automation strategy is the use of Automated Fibre Placement (AFP). This technique uses the selective placement of narrow carbon or glass fibre tapes to construct a composite laminate. Popularised in the aerospace industry, AFP improves productivity whilst providing high accuracy and quality as well as reduced wastage [22]. Hence, AFP has the potential to produce wheels at a lower cost and faster rate than currently used processes.
This study demonstrates the analysis and design of a carbon fibre reinforced composite wheel for the Sunswift 7 solar racing car made using a hybrid approach by combining AFP and hand layup techniques. This prototype design aimed to evaluate the feasibility of incorporating AFP into the wheel production process and simultaneously demonstrate the thick laminate with selective reinforcement manufacturing capability of automated fibre placement. A detailed analysis is carried out using ANSYS ACP PrepPost. The wheel geometry is optimised to reduce deflection from vehicular loads. VERICUT Composite Programming/Simulation (VCP/VCS) software was used to check manufacturability of the optimised design with AFP. The manufactured wheel is tested for deflection and strain and compared with the predicted results. The manufactured wheel weight was 3352g and provides a valuable insight into thick laminate manufacturing and the integration of AFP into car wheel design.