A Study On Crashworthiness Of The Front Longitudinal Beam Based On Plate Strain Rate And Precision Of Spot Weld Model

In2011, the output of Chinese auto industry has broken though18,400,000, whichtakes the first place in the world. Therefore, safety of vehicles has become one of the keyfactors to the further development of traffic transportation and auto industry in China. Inorder to prevent traffic accidents, more and more countries take the measures to enhancevehicle crashworthiness by initiating auto safety laws and New Car AssessmentProgramme (NCAP).This thesis is mainly to improve crashworthiness of front longitudinal beam throughanalysis of the influence of spot-weld models simulation types and the plate strain rate onthe simulation results. So we can improve the accuracy in the simulations ofcrashworthiness of front longitudinal beam, which can provide the reliable parameters fordesign of front longitudinal beam..Base on the literature study on frontal longitudinal beam crashworthiness, it isintroduced for the research status at home and abroad with impact test and simulationanalysis method. A summary was presented for the car frontal crash laws and regulations.The frontal impact involving multiple components and systems. A brief introduction wasdone for the front of the car crash finite element theory and algorithm. In this papercomprehensive application of finite element analysis and sled test was identified. In orderto ensure the accuracy of longitudinal beam simulation，the simulation analysis of frontlongitudinal beam crash utilizes finite element method via suitable definition of theparameter of critical time step, hourglass modes, grid spacing, and friction force of mainand subordinate node, and the material property, including material constitutive relations,contact issues handling and so on.Use a variety of spot-weld model for establishment of longitudinal beam and crashtrolley models, which was used to study the different categories of spot-weld model usedin the longitudinal beam. According to the analysis of5kinds of welding simulationmethod, and the comparison of the characteristics between model and actual test results,the deformable beam element model is a good spot-weld simulation model.Through static and dynamic tensile test, the stress strain curves under the differentstrain rate were generated, and then the effect of crash simulation on longitudinal beamwas investigated under different strain rates in combination with the material curve and simulation results. Based on the results, the simulation analysis has to be conducted bysetting different CP values according to the actual conditions and material properties.For the problem of pull-out failure of spot weld of longitudinal beam at front crash,it can be solved by considering of the strain rate and spot-weld simulation. A optimizationof spot-weld layout of longitudinal beam was conducted using the experimental designmethod, which lead to good effect on the result. The analysis indicate that the differentspot-weld layout have a great influence on longitudinal deformation and energyabsorbing. Too big and small layout of spot-weld are not conducive to the longitudinaldeformation and energy absorption.