Design and Optimization of Carbon-Fiber Chassis Panels

Each year, the Virginia Tech (VT) Formula SAE (FSAE) team creates a high performance car to compete against 120 teams from around the world in a series of dynamic events evaluating acceleration, maneuverability, and handling. In an effort to improve upon the VT 2013 car, the torsional stiffness of the chassis was increased. Increasing the torsional stiffness of the chassis allows the suspension to be more precisely tuned, resulting in a better overall performance. An investigation was conducted into methods for improving the chassis stiffness, and it was determined that many state-of-the-art vehicles from go-karts to super cars incorporate strength-bearing, tailored advanced composite materials in their structure. Examples of components that use composites in vehicles include sandwich structures in load-bearing panels, layups in the skin of vehicles for aesthetic purposes and carbon-fiber frame tubes. The VT FSAE car already includes untailored carbon-fiber panels on the bottom and sides of the structure for packaging and aerodynamic purposes. By integrating and optimizing these carbon-fiber panels, the torsional stiffness and therefore overall performance of the structure may be increased.

This thesis explores composite testing, optimization methods, experimental and computational analysis of the chassis, and results. The fiber orientation of the panels may be optimized because carbon-fiber composite materials are generally anisotropic. Therefore the composite materials can be tailored to maximize the stiffness, resulting in the optimum stiffness per added weight. A good measure for testing stiffness per added weight is through measuring natural frequencies because natural frequency is proportional to stiffness per unit mass. A computer program was developed in MATLAB to optimize the composite configuration, and uses an objective function involving the first three natural frequencies of the original steel space frame chassis and the first three natural frequencies of the steel chassis augmented with three composite panels. The composite material properties were determined using specimen tensile testing and checked with finite elements. The natural frequencies of the half-scale chassis were determined experimentally, compared to the simulated version, and varied by less than seven percent. The optimization of the full-scale model determined that eight layers of optimized, integrated carbon-fiber composite panels will increase the first, second, and third natural frequencies by sixteen, twenty-six, and six percent, respectively. Natural frequency increases of these amounts show that by using tailored, load-bearing composite panels in the structure, the torsional stiffness of the structure increases, resulting in easier suspension tuning and better performance at the VT FSAE competitions.