Design teams need to understand the loads their race cars experience on the track. Many raceways focus on track uniformity, so the loads experienced by cars are generally well understood.
For Baja off-road racing, however, loads can be drastically different for each race due to the track’s varying terrain and obstacles.
“Some races are wet, others are bone dry. You’re going up and down hills for hours. The engine’s hot, the driveline’s hot, the vehicle’s hot and you’re driving on the track with a hundred other cars. People can hit you, spin out and become obstacles themselves. Surviving this race is about driver skill, but it’s also about how well your car can survive a variety of loads,” says Colton Johnson, system simulation engineer at Rochester Institute of Technology’s student Baja team (RIT Baja).
Johnson explains that the teams that understand their car’s loads are consistently ranked at the top. He should know: His simulations played a part in helping RIT Baja win the top spot in two of the SAE Baja races in 2018. As for his simulation-savvy competition — they weren’t far behind, with RIT Baja winning the North American title by just 2 points out of a season total of 3,000.
To stay on top, RIT Baja needs fast and cost-effective ways to test its car to reduce the vehicle’s weight. Empirical testing is often too expensive and time-consuming for the team of students.
Johnson says the best way to understand the car’s loads is through the free simulation software provided by ANSYS’ student team sponsorship.
Understanding the Fatigue Failure of Off-road Vehicles
To compete effectively, RIT Baja needed quick answers to assess why many of its old parts were failing.
“When I joined, I was fortunate to inherit the task of developing driveline simulations,” says Johnson. “We wanted to mitigate failure due to fatigue and vibration because in prior years it caused some lightweight components to break. Our knowledge of simulation and analysis is growing rapidly, allowing us to tackle and diagnose items that were holding us back.”
RIT Baja turned to ANSYS Mechanical to perform the modal and structural simulations needed to assess the high stress areas in the car. The team found that the areas of high stress overlapped the areas where the parts were failing.
“Using the same simulation parameters, I assessed how our new designs would perform,” says Johnson. “The stress concentrations in the newly designed system were outside of our areas of concern and the components with these concentrations were well equipped to handle the loading.”
Since the stress concentrations are no longer an issue, RIT Baja can reduce the size of other components while maintaining safety.
“As a result,” Johnson continues, “this year’s car is lighter and strong enough to survive all of our races. The components we studied with ANSYS have surpassed their expected life and keep us in the competition.”
Finding Unknown Load Cases from Simulation and Part Failures
Simulations also help RIT Baja diagnose the loads that are causing failures. These loads would otherwise be difficult or impossible to identify.
For example, RIT Baja can analyze a buckled shock mount and determine the load that caused the issue. Once the load is better understood, RIT Baja can optimize the part to survive that load.
“We perform static structural simulations with different loads,” says Johnson. “We then use ANSYS’ eigenvalue buckling tool to find out which loads cause that type of failure.”
After all, it’s better to learn about the load during testing — so you can address it — than to have a broken car on race day. But if a car does break on race day, you want to know why so it doesn’t happen again.
Simulations Can Help Teams Design Light, Strong Cars
Lighter cars are faster and more efficient. RIT Baja aims to make its car as light as possible while maintaining a good factor of safety.
RIT Baja does this is by performing simulations to ensure the torsional and impact rigidity of the car’s frame.
“Our frame designer allows for deflection tolerances that are based on expected load cases and drop scenarios,” says Johnson. “We then develop simulations as a group to validate the frame. “
“The goal is to have the frame keep its shape and rigidity based on these inputs,” he adds. “We aim to make it as light as possible without causing the frame to affect the rest of the vehicle’s performance.”
Currently, RIT Baja’s simulations have helped it improve its frame to the point that it can now reliably survive intense drop tests without failure.
To see how your student team can optimize its designs, try out ANSYS’ Free Student Software or apply for a student team sponsorship. If you are looking for technical help, join the ANSYS student community.