A systematic approach for multi-objective lightweight and stiffness optimization of a car body

Optimization for the car body under the condition of guaranteeing vehicle overall mechanical performance remains a key automotive engineering design challenge currently. The present study first attempts to group the car body components into safety components (SCs) and non-safety components (NSCs) based on their correlation with crashworthiness safety and then focuses on the potential of NSCs, which compromise a group of thin-walled plate parts that basically have little impact on overall vehicle crashworthiness, for multi-objective lightweight and stiffness optimization. To be more specific, the finite element (FE) models of significant vehicle performance, including the static-dynamic stiffness of the car body and the frontal and side crashworthiness of the vehicle, were first separately established and validated against experimental outcomes. On this basis, SCs closely related to vehicle crashworthiness safety, including frontal safety components (FSCs) and side safety components (SSCs), were figured out through crashworthiness analyses. As a result, the initial NSCs (INSCs) were also determined by filtering out all the SCs from the car body. Subsequently, sensitivity analysis (SA) was employed to screen the INSCs for the final NSCs (FNSCs) for multi-objective lightweight and stiffness optimization, considering minimizing the total mass while maximizing both the static global torsional stiffness and the dynamic first-order torsional frequency of the car body as three optimization objectives. Radial basis function (RBF), multi-objective particle swam optimization (MOPSO) algorithm and modified grey relational analysis (MGRA) were then separately utilized for constructing meta-models, solving optimization process, and identifying the best trade-off design. In addition, different optimization strategies were compared. According to the optimized outcomes, the car body is dramatically lightweight optimized by 7.92 kg; meanwhile, the static-dynamic stiffness of the car body is slightly improved and the overall vehicle crashworthiness is basically guaranteed. Hence, the proposed systematic approach gains insight on reasonable and efficient multi-objective optimization for the car body.