MUR Blog - 2019 Altair Carbon Rim Simulations

Each year, SAE-Australasia organises a student design competition wherein, a team of student’s present a formula-style race car, that they conceived, designed and manufactured during the past year. During this endeavour, the students gain real-world applicable experience, in teambuilding, organisational management, self-discipline and car design. All of which they need for a prospective career in the automotive sector, as well as other engineering fields.

As one of the first competitors, Melbourne University Racing (MUR) has a long and successful history in the F-SAE- Australasia competition. In 2019, the team prioritizes more points in the dynamic events, which has been identified as an area of most improvement. While 2018 was a momentous year for the team, with MUR’s first electric vehicle competing alongside its combustion car, the pursuit for more competition points drove the team to reduce the mass of the 2019 cars.

The team partnered up with Altair and their HyperWorks package to design a new Carbon Fiber wheel. The suite of engineering tools, particularly the Hyperlaminate and Optistruct functionalities, facilitated rapid optimisation of composite parts that keep manufacturing in mind the way through, resulting in a complete design that is ready for layup.

HyperMeshWorkspace Figure 1: HyperMesh Workspace

MUR18C

Figure 2: MUR18C

Team

MUR is a student-run team comprising of over 100 members, all contributing to the various subsystems found on the MUR19 competition car. The team is structured into design, integration and management. Design engineers are dedicated to a system, then integration engineers take care of the vehicle subsystems, leading their respective designers. Management has the responsibility for the overall vehicle design and running of the team in non-technical aspects.

Challenge

The aim was to decrease the unsprung mass of the car, by manufacturing the wheel rim’s out of composite materials. The reason for this was the large competition points gain from decreasing vehicle mass, and further gains are realized for decreasing unsprung and rotational mass. Completing this within imposed competition rules, team capabilities, resource and time constraints means the design iteration needed to be quick, as to allow adequate brainstorming, manufacturing and testing time.

Solution

Several steps were taken by the design engineer to reach the conclusion in HyperWorks. First, hand calculations were performed on the barrel and end disc of the largest half-barrel found in the rim package. After this was done, a CAD model and FEA setup were undertaken in HyperMesh, to replicate the hand calculation’s model with fewer assumptions, primarily the Bernoulli-Euler beam theory and Roark’s circular loading theories, along with the isotropic material assumption for hand calculations. After satisfactory validation of hand calculations, the design engineer understood the ballpark stresses and deflections to expect when the true wheel CAD was used.

FEAHandCalcVerified

Figure 3: Hand calculation’s model, used to verify FEA model against hand calculations

Next is the optimisation of the ply layups, on the final wheel shape. A free size optimisation sweep was conducted, which results in the best shapes for each angle ply, considering the loading conditions, for minimum compliance with mass, deflection and fatigue constraint. The fatigue life of the rim is also analysed in HyperMesh for 3 years of life. Following a clean-up of the shapes, a size optimisation was performed to find the optimal thickness of each angled ply, along with keeping within 10% of the optimised stiffness found in the free size optimisation and minimizing mass. Finally, a shuffle optimisation is used to find the best stack up sequence for the carbon-fiber plies.

FEAModelForcesVerified

Figure 4: FEA model with forces and RBE3 elements to transmit the forces

FEAResultsHyperGraph

Figure 5: FEA results in HyperGraph. This result is used in optimisation to reduce the mass of the wheel

This final design achieved the goals of the lightest wheel along with designing for manufacture in mind. The details of the laminate can be readily used by the manufacturing team to lay up the wheels on a mould.

Results

The optimisation will be paired with the competition analysis done on the recent FSAE-Australasia event, in order to gain the most points possible, not just the lightest design. With this in mind, the following figure shows that any decrease in the amount of Carbon Fiber used for the wheel’s package, the more competition points the car will earn, even considering the cost of materials and manufacturing.

CompPointsVsCarbonLayers

Figure 5: Plot of the increase in Competition points versus the number of layers of Carbon Fiber used for the 4 wheels. The cross-over point was found to be around 23 layers of Carbon Fiber, of which there is no gain in competing with Carbon Fiber wheels

Next Steps

The design is currently nearing completion, meaning the manufacturing process is ramping up. Due to the design process conducted in Optistruct, the layers are ready to be cut by the team from Carbon Fiber ply, and the mould will be sent off to be machined. This will allow the two half rims of each wheel to be manufactured and assembled, as designed, assuring design fidelity.

Author:

JoelMillar

Joel Millar

Junior, 2019