Multi-objective Optimization For The Aluminum Vehicle Door Based On The Equal Stiffness

Recently, the light-weight design of vehicle becomes a hotspot in research work.Light-weight of vehicle can reduce the fuel consumption, improve the fuelefficiency and cut down the emission. Vehicle door, as important closures of thevehicle BIW, requires sufficient stiffness and appropriate vibration and relevantdurability. At present, there are three approaches to reduce the weight of the door:shape optimization, light-weight materials substitution and the advanced formingtechnology. Aluminum alloy is one of the common materials served as light-weightsubstitution. Under the premise of the good performance, the door achieves highmass reduction by replacing the steel with aluminum alloy as the raw materials.This work outlines a procedure to substitute the steel with aluminum alloy for thevehicle door design based on the analysis of the low er and upper torsion, verticalsag and natural frequency. The door parts are optimized through sensitivity analysis.The approximation model is established through experiment and surface responsemethod. The lightweight design method for the lightweight ma terial substitution isproposed based on the equivalent stiffness. The aim of this work is to have anoptimized design of the vehicle door though the replacement of the aluminum alloyas the material, providing the good performance of the door. The context of thepaper includes:(1)The finite element model is established in this dissertation, then the originalresponse of the lower and upper torsion, vertical sag and natural frequency areanalyzed by finite element (FE) model in corporation with the verification of therelevant physical experiment. According the sensitivity analysis of the lower andupper torsion, vertical sag and natural frequency,17parts are sequenced anddiscussed respectively. Due to the limitations of direct sensitivity, all parts aresequenced and discussed again in the light of the relative sensitivity value.According to the above analysis and the door structure,9parts are finally selectedfor the lightweight design.(2)The approximate expression is adopted to replace the door mat erial from steelto aluminum alloy based on the equivalent stiffness. Coefficient of light-weight η,is calculated. The substituted aluminum alloy door is re-analyzed in terms of thelower and upper torsion, vertical sag and natural frequency. (3)Latin square experimental design is used to sample different values form thelower and upper torsion, vertical sag and the first-order modal. According tosamples, the second order response surface models which contain9variables areestablished by the least squa re method. After accuracy testing, the approximationmodel can be used to replace the finite model for the optimization.(4)The aluminum alloy door is optimized by the multi-objective geneticalgorithm when the door weight and the sag displacement are the targets as well asthe replacement of the lower and upper torsion and first-order modal are theboundary conditions. Then the non-Pareto optimal set is established. According thestructure and forming technology, an appropriate solution is selected from th e set.Finally, the optimization results are verified to satisfy the relative standard via thefour working condition FE analysis.