Crashworthiness Design Of Front Longitudinal Beam Based On The Crushing Deformation Theory Of Thin-walled Structures With Top-hat Section

Rapid development of automobile industry in improving human life at the same time brought such as traffic accidents,environmental pollution,energy crisis and other serious social problems.Car crash safety has gotten attention of the whole society due to the relation with the life safety of occupants and pedestrians.It is well know that front longitudinal beam(FLB)is the most significant deformable part and energy absorption under vehicle frontal impact loading.In other words,the quality of the vehicle crash acceleration response and the size of the crew capsule invasion amount are determined by the energy absorption and deformation mode of FLB,especially in the front high speed crash conditions.Due to stricter safety regulations,the crashworthiness design problem of FLB has been the new research hotspot.As the important energy absorption of car body,thin-walled structures with top-hat section(TWS-TH)are widely used in car crash safety due to the quality of high strength and good energy absorption effect,light weight,etc.In car collision accident,thin-walled structures undergo complex force and show complex form of deformation of crushing.The bending crushing and axial crushing are two typical forms of deformation of TWB.Therefore,analyzing bending crushing and axial crushing deformation mechanism of TWS-TH,establishing corresponding theory prediction model of energy absorption,exploring reasonable deformation order and the condition of stability conditions have been theoretical basis of crashworthines s design of FLB.The main research works in this thesis are:(1)An improved quasi-static bending crushing and axial crushing theory model of TWS-TH was proposed,and the corresponding energy absorption formulation were derived based on the Kecman crushing theory of TWS and Wierzbicki super folding element(SE)theory.The theory model proposed in this paper can solve the problems of bending crushing and axial crushing energy absorption of TWS-TH which have same thickness and material,same thickness an d different material,different thickness and same material,different thickness and material.The accuracy and generality of theory model are verified by the way of combining experiment and simulation.(2)Analyzing the yield criterion of bending crushing and axial crushing.Then,establishing simplified model of TWS-TH.Obtaining the condition of bending crushing and axial crushing of TWS-TH under combined loading of compression and bending by analyzing the stress distribution.(3)First,establishing typical variable cross-section finite element model of TWS-TH,exploring the influence regulation of different variable cross-section angle and excessive surface radius has on resistance to bending of cross-section TWS-TH by the way of simulation.Than exploring the influence regulation of the cross section parameters of flange width,width of section and height of section have on deformation stability of cross-section TWS-TH.Finally,the reasonable design range of each structure parameters were obtained while TWS happened reasonable deformation order and stable collapse.(4)Establishing initial simple mode of FLB with top-hat based on the research achievements in the fourth chapter and its initial impact performance was analyzed.The surrogate model has been built by means of experimental design and the initial crashworthiness optimization design has been executed by the multi-objective method and the initial optimization model was obtained.Finally,the second optimization model was obtained based on the s tructural feature design of initial optimization model.The crashworthiness design methods of this chapter was verified by comparing the collision performance of three kinds of structure state of FLB.