Simulating Dynamic Vehicle Maneuvers Using Finite Elements For Use In Design Of Integrated Composite Structure

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Virginia Tech

Formula SAE (FSAE) chassis systems are increasing being manufactured with integrated composite structures in an effort to increase the performance of the system while decreasing weight. The increased use of composite structures requires more details of the loading conditions and evaluation metrics than the mild steel structures they are replacing. The prototypical FSAE steel space frame chassis designs are heavily structured around the mandated safety rules that doubled as mostly satisfactory structures for vehicle loads. The use of composite structures and the directionality of their material properties has created a need for more detailed loading scenarios to evaluate their ability to transfer load.

This thesis presents a framework for evaluating the chassis structure not only through the standard static twist analysis, but increased use of modal analysis and dynamic vehicle maneuvers using an attached suspension. The suspension joints and springs/dampers are modeled using Abaqus Connector Elements, allowing for the use of complex kinematic degrees of freedom definitions required to accurately model the suspension behavior. The elements used to represent the joints and springs are detailed as well as their superiority over traditional multi-point constraints in this context.

The use of modal analysis is used for a more direct comparison of not only the efficiency of stiffness in the chassis alone, but also how the chassis interacts with the suspension. The natural frequencies from the modal analysis along with the static twist distribution along the chassis are presented as a replacement for the static torsional stiffness performance metric.

By using dynamic vehicle maneuvers the chassis-suspension structure can be evaluated based on loads developed during the typical use of the FSAE vehicle. The dynamic nature of the analysis also allows for the inclusion of mass in the loading profile as well as the load variation with time that can be hard to achieve with static analysis. The framework for a bump event as well as a constant-speed-constant-radius turn are presented. The bump analysis is designed to evaluate the system's response to straight line dynamic events, while the turning maneuver evaluates the lateral components of the suspension load transfer capabilities. For the turn analysis both a spring/damper tire model using connector elements and a rolling tire model are presented. Intermediate checks on suspension and chassis behavior are evaluated to verify the modeling techniques; while the maneuver results are evaluated based on trends and overall motion rather than magnitudes due to lack of data at the time of the analysis.

FSAE, Finite Elements, Vehicle Maneuvers, Composites