| With the progress of the automotive industry and the improvement of the competitive pressure of the automobile market,in order to enhance the brand effect of the company and keep the updating speed of the product,it is no longer satisfied with the design and production cycle just by the traditional vehicle test methods.The test means which combine CAE technology and indoor test rig can effectively reduce research and development costs and shorten the production cycle,getting widely used in automotive enterprises and universities.As a vital component in vehicle,sub-frame can not only reduce vibration and noise,but also bear the body deformation.In order to ensure its reliability,fatigue test is an indispensable part in production design.Compared to the test rig,the actual road tests are more accurate,as a results,the sub-frame test rig must ensure that the force characteristics of the sub-frame on the test rig are consistent with the actual vehicle,so that the test rig able to simulate road test.This paper is based on a cooperation project: the development of front sub-frame test rig and research of its fatigue life.A car front sub-frame is selected as the research object,then optimized and designed fixture of the sub-frame fatigue test rig,and corresponding experimental verification is carried out.The contents of study are as follows:(1)Establish the finite element model of the sub-frame and BIW system.The geometric model of the front sub-frame and BIW are introduced,and the finite element model is built through pre-processing and element checking.The static test of the sub-frame and BIW system is carried out.According to the test conditions,the model is restrained and loaded.Compared with the simulation results and test results,it is found that most of points stress error values are within 20%,and the simulation models basically meet the accuracy requirements.(2)The multi-objective optimization of the test rig for the sub-frame.Based on the system identification,and the sequential quadratic programming algorithm,the sizes of test rig fixtures section are selected as the design variable,meanwhile,the static simulation stress values of the sub-frame and BIW system are taken as the objective in the process of fixture optimization.After 236 iterations,the optimal fixtures size of the test rig were obtained.(3)Static test of the sub-frame test rig.In order to verify the accuracy of optimization,carrying on static test of the sub-frame test rig,the results of test are compared with subframe and BIW experiment.It is found that majority of the strain stress value error is less than 10%,achieving our design target.At the same time,the FEA results are compared with the test results,both of which are sub-frame and test rig system,the results show that the error among most of them are less than 20%,meeting the simulation requirements.(4)The fatigue life analysis of the sub-frame and fatigue life test.According to the load spectrum provided by the enterprise,the S-N curve fitting according to the material characteristics of QSTE420 TM,the fatigue life of sub-frame is analyzed.The minimum fatigue life of the sub-frame is 283 cycles,which amounts to 98201 kilometers.Due to the limitation of the S-N curve of the material and the parameter setting of the weld in fatigue analysis,there will be error in the analysis process.The fatigue life test of the sub-frame was carried out based on the sub-frame fixture we optimizing.The test results show that most of the crack regions are reflected in the fatigue life calculation. |
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