Multidisciplinary design optimization of a zero-emission vehicle chassis considering crashworthiness and hydroformability

This research used multidisciplinary design optimization to optimize the ladder frame chassis of a zero-emission vehicle by simultaneously considering three objective functions: (a) chassis mass, (b) deceleration during collision, and (c) manufacturability of a part in hydroforming. Additionally, design constraints were placed on torsional and bending stiffness, maximum von-Mises stress, and the natural frequency in torsion and bending. Optimization was completed in a three-phase approach: phase one used a simplified chassis model to conduct topology optimization with genetic algorithms; phase two was conducted to determine an optimum cross-sectional type and shape; and phase three incorporated results from phases one and two, into a high-fidelity, three-dimensional chassis model, for gradient-based optimization. Results from all phases of the design optimization indicated that improvements could be made over the baseline configuration. Through examination of Pareto frontiers in phase three, distinct trade-offs were identified between all objective functions: a 5 per cent reduction in chassis mass was required to maximize hydroformability; to minimize mass required a 90 per cent increase in deceleration; and minimization of deceleration required an 18 per cent decrease in hydroformability. Tri-objective optimization was used to generate a three-dimensional Pareto frontier ‘surface’ to show the impact of one objective function on all others simultaneously.