Abstract: Aiming at the lightweight design of car body structure in concept design phase, a hierarchy iteration optimization scheme is proposed which can realize multi-material structure design of car body. In the optimization scheme, the design variables include the topology connection beside panel thickness and material as usual, for meeting the requirements of ‘putting the right material on the right position’. In the first layer of hierarchy iteration optimization, with topology connection as design variable, graphic decomposition and NSGA-II are adopted to conduct multi-objective optimization on the topology structure in car body assembling, maximizing the bending and torsional stiffness and the first-order natural frequency of car body. In the second layer, multi-objective optimization is performed on panel thickness and material, minimizing the mass of car body and material cost. Finally, fuzzy set-based scoring formulae are used to select the comprehensively optimum solution, achieving the light-weight design of car body structure with cost consideration

Key words: lightweighting, multi-material, graphic decomposition, hierarchy iteration optimization