Multi-objective Optimization Methods In TheLight-weight Design Of The Auto-body Structure

The lightweight technology of auto body has been the automobile industry's difficult and hot because the more and more strict regulations require of the car emissions, fuel consumption, crash safety, and so on.Usually there are three ways to get the lightweight automobile body structure, through body structure optimized design and innovative design,the development and application of light weight and high strength body material, and using advanced body manufacturing technology. Due to the comprehensive advantages in the performance of the strength, toughness, impact resistance, recycling and cost, high strength steel and advanced processing technology has become the most important way of lightweight design body structure.High-strength steel body structure design is a multi-disciplinary and multi-objective optimization process including stamping, impact safety, structural strength, mode and stiffness, NVH and aerodynamic performance requirements and other aspects.According to the needs of lightweight body structure designs, the paper carried on the elaboration to the multi-objective optimization theory, including the experimental design, agent model, modern optimization algorithms, and the quality engineering. In this thesis, the research work include the following three aspects:1)Through the analysis of the body structural feature, the front and side collision deformation characteristic, and the collision force and energy power flow distribution studied,it proposed the automobile body structure high strength steel plate distribution plan,and enables the high strength steel plate quality proportion up to 54%, the domestic leading level.2) It also proposed the processes and methods of the multi-objective optimization in the body structure design. To match the automobile body front part structure's material and the geometry size after the application of high strength steels, first the finite element model of the body in white and the 40% offset frontal impact model were established; second, the property indexes such as the torsional stiffness of entire body in white, the maximum impact force and the mean force, the collision energy absorption and the minimum mass were considered in the optimization model at the same time, then used the non-inferiority hierarchical genetic algorithm (NSGA-Ⅱ) to carry out 6σreliability optimization design based on the high-precision response surface approximation model;at last, using Monte Carlo simulation technology to evaluate the robustness performance of the result. The optimization results improved the vehicle's collision safety performance, the deformation mode of the front side parts is more reasonable, and the acceleration response in the rear door sill is also improved.3)The comparison between experiment and simulation of the Body-In-White and 40% ODB offset-crash show that the finite element model meet the requirement of engineering design.The simulation results of 40% offset crash results also shows that all collision response target had been obviously improved after material upgrades and structure improvements.Light-weight coefficient had decreased from 5.23 to 4.67, which is the domestic leading level.