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AUTOMOTIVE & MOTORSPORT
Simulation speeds rollcage design process The need for speed is what racing is all about. However, before cars even make it onto the tracks, the teams, vehicle fabricators and component manufacturers must ensure that the vehicles are safe – and adhere to the strict regulations set forth by the appropriate governing bodies. Just ask Brett Longhurst, owner and Managing Director of Bremar Automotion. Based in Carrum Downs, Victoria, his company provides simulation, testing, validation, and design optimisation services to customers across many industries, including automotive and motorsport. In particular, Bremar is accredited by the Fédération Internationale de l’Automobile (FIA) the world governing body for motorsport, to certify vehicles’ rollcages using finite element analysis (FEA). This accreditation enables the company to independently certify rollcages for competition use both here in Australia and internationally.
Life savers Rollcages protect occupants from being injured in roll-overs and other accidents that sometimes occur in the heat of competition. They can vary greatly in design, depending on the level of racing and the type of racecar. For example, a rollcage for the Australian V8 Supercar Series – based around General Motors and Ford production cars – is very different from a rollcage built for off-road racing vehicles. Depending upon the type of vehicle and race category, there are also different requirements on which bars, materials and types of reinforcement are used. “The rollcage regulations that we work to generally depend on the vehicle weight,” says Longhurst. He adds that the grade of material often governs the complexity of rollcage design. For instance, a cage made out of lower-grade steel will usually require thicker material and more tubes, which generally leads to a heavier structure. A higher-grade steel such as chromoly, however, has a much higher strength, so the tubes can be thinner to reduce the overall weight of the rollcage structure, but would come at a greater cost for materials and fabrication time.
Bremar Automotion created this rollcage design concept and CAD overlay for a Side By Side (SxS) off-road race buggy.
AMT DEC 2021
“Like any engineering design, the factors affecting product development, such as weight, strength and cost, are always playing off each other and have conflicting impacts on the design,” continues Longhurst.
Design and certification When customers approach Bremar Automotion about developing a new rollcage, the first step in product development is often to perform a 3D scan of the vehicle and/or its interior to determine where the rollcage will be placed. The Bremar team then packages specified vehicle sub-systems and components within a CAD model – including information on the driver and steering wheel, among others – and provides an initial rollcage design and tube sizing. In some cases, a mock-up of the rollcage is created with plastic tubing to ensure that the driver can get into and out of the car, that there’s sufficient head clearance, and that the rollcage is not impeding the driver’s ability to steer or reach vehicle controls. It’s often difficult to judge these ergonomic factors in CAD, so a physical mock-up in the vehicle is often the simplest and most accurate way for the driver and team to confirm it meets the requirements. Once the team is satisfied with the design, a drawing of the rollcage is submitted to the governing body for the racing category. “Before we go through the process of doing the analysis and building the rollcage, we want to get confirmation that it is actually compliant with all other aspects of the regulations,” says Longhurst. Once the governing body provides in-principle support for the design, Bremar creates FEA models of the rollcage, applies the various load cases, and assesses the results against the required acceptance criteria. If the rollcage doesn’t initially meet the requirements, the analyst can easily alter the design by thickening a tube or placing a bar in a different location and rerunning the simulation. Once the design has been approved, the rollcage is built by the customer or manufacturer. If there are any changes made during the build process, Bremar updates the simulation models and does another round of FEA to ensure that the final as-built structure is still compliant with all the requirements before issuing a certification report.
