Abstract:
This paper describes the design, FEA, and verification processes undertaken by Lawrence Livermore National Laboratory (LLNL) and Kaiser Aluminum for a prototype electric vehicle's CALSTART Running Chassis. The goal was to use lightweight aluminum extrusions for the vehicle’s load-bearing structure while maintaining structural integrity and crashworthiness. Leveraging its traditional mission in finite-element code technology for weapons design and safety, LLNL collaborated with Kaiser Aluminum on this study. The work focused on component-level studies, including the effects of rail geometry, size, and thickness on crash energy absorption. Using the DYNA3D finite-element code, the team numerically reproduced the experimental finding that crush energy absorbed by tubes varies with thickness raised to the power of 1.6 to 1.8. This provided the confidence to study the crashworthiness of a complete aluminum spaceframe.
The analyses explored various design iterations for frontal impact at moderate and high speeds. The study examined the performance of the spaceframe itself, as well as the additive effects of the powertrain cradle, motor, and suspension. A major challenge identified was the lengthy powertrain assembly, which could impede a smooth crash pulse. This was addressed in design iterations, such as "Design M," which forced the powertrain into motion earlier during a crash to minimize high G-forces transferred to the cabin, resulting in a significantly improved crash pulse compared to "Design K". The paper also details the development of the finite-element model using PTC ProEngineer and TrueGrid, which prepared the mesh for the DYNA3D code. Additionally, FEA was used to simulate and verify roof crush analysis according to FMVSS 216 standards, ensuring the proper extrusion thicknesses were chosen for the roof structure. The analysis showed that the roof could easily surpass the requirement of withstanding a force of 1.5 times the vehicle's curb weight. The use of FEA allowed for efficient evaluation of numerous design permutations and crash scenarios, demonstrating its critical role in optimizing the vehicle's safety features.
