Study On Axial Crashworthiness Of Aluminum Alloy Thin-walled Tubes With Rectangular Unequal Multi-cell Cross Sections

As a crucial part in vehicle BIW,the front beam tends to absorb crashing energy by crushing deformation when frontal impact occurs,so as to protect the powertrain and passengers in a car.Traditional front beams are invariably metal thin-walled tubes with rectangular cross-sections.However,researches point out that,when subjected to axial crushing compression,rectangular thin-walled tubes with complex cross-profile exhibit better energy absorbing performance than plain ones.Therefore,complex cross-sectional tubes(e.g.multi-cell tubes)have attracted attention from increasing number of scholars.This paper provides an investigation on axial crashworthiness of aluminum alloy thin-walled tubes with five types of rectangular cross-sections,namely single-,doubleand triple-cell columns and 2x2,3x3 sectional tubes.Moreover,this paper offers optimization designs for tubes with complex sections(triple-cell and 3x3 sectional columns).Firstly,crushing deformation and energy absorption mechanisms of metal columns under axial loading are analyzed.Based on existing theory,a formula for predicting mean crushing force of rectangular unequal triple-cell tube is derived.Then,the quasi-static axial crushing finite element analyses(FEA)are conducted on tubes of normal and multi-cell profiles respectively.In addition,in order to initially explore structural parameters’ influences on crashworthiness,thicknesses and internal layout parameters of triple-cell,2x2 and 3x3 sectional tubes are selected for parameter analysis.The forth,on the basis of parameter analysis,triple-cell tube and 3x3 sectional tube are chosen as optimization models.Three wall thickness parameters and one layout parameter for triple-cell tube,two wall thickness parameters and one layout parameter for 3x3 sectional tube,totally 4 and 3 structural parameters are selected as variables;mean crushing force(MCF)and specific energy absorption(SEA)are optimization objectives,and the optimal results are obtained from Pareto frontier.Finally,robust optimization is conducted and robust solution is acquired.The comparison among results from theoretical prediction,FEA and experiments,on the one hand,validates accuracy and reliability of FEA models and newly derived prediction formula;on the other hand,shows that triple-cell tube and 3x3 sectional tube have better crashworthiness than others.Through structural parameter analysis and the establishment of surrogate model,it has been found that wall thickness and layout of internal ribs have noteworthy influence on structural crashworthiness.In addition,the optimal results of deterministic optimization show that the optimized triple-cell and 3x3 sectional tubes have better thicknesses distribution and internal layout,therefore,crashworthiness has been significantly improved compared with initial design.Nevertheless,the robustness of deterministic optimization remains at a relatively low level due to the deviation of manufacture and material properties.Finally,the robust optimization design has been conducted on triple-cell and 3x3 sectional tubes.It can be noticed that robust results show increase of robustness with tiny sacrifice of crashworthiness.