Abstract: In order to achieve the precise optimization of the front floor composite layup of the body-in-white as well as the level of structural lightweighting,a multilevel combination optimization and design method based on the body-in-white is proposed,which adopts a partitioned carbon fiber composite flooring strategy to individually design the layup of the front floor of the carbon fiber composite material. A finite element model of an electric vehicle body-in-white is established to verify the correctness of the model. Through the mechanical property test of carbon fiber composite materials,the mechanical parameters of the T700/WP-R2300 resin-based fiber-reinforced materials are determined. The super-layer free size optimisation,ply block cutting and ply block size optimisation methods are used to determine the ply thickness,ply block shape and ply layer number of the carbon fiber composite front floor,and the ply lay-up sequence is adjusted through ply sequence optimisation,and is placed in the body-in-white to carry out simulation verification. The results show that the static bending stiffness and static torsional stiffness of the carbon fiber composite front floor after paving design are 198.69 % and 153.59 % higher than those of the original steel floor,and the effect of lightweighting is remarkable. The optimized carbon fiber composite front floor reduces weight by 45.33 %. At the same time,the static bending and torsional stiffness of the body-in-white are increased by 1.82 % and 1.96 % respectively,and the first-order bending and torsional frequencies are increased by 3.05 % and 3.72 % respectively,and the static stiffness and low-order modal performance are significantly enhanced.

Key words: body-in-white static performance, carbon fiber composite front floor, multilevel optimization approach, layup sequence optimization, lightweight design