The Fatigue Life Prediction Of Car Body Structure Based On Real Road Spectrum

When a car is running,because of the influence caused by uneven pavement and pavement itself in defects and other factors,the body structure is affected and leaded to failure by alternating load.As an important bearing part,the performance fatigue durability of the body structure is an important aspect of the safety performance of vehicle.At present,although the research on the durability of the body based on real vehicle road spectrum started earlier in the foreign country,foreign road conditions and the driving habits of users are different from the domestic,the durability cases may not be suitble for Chinese users.The research on the durability of the body based on real vehicle road spectrum is less and started late in domestic.Therefore,it is urgent to establish a durabiltiy development system of automobile body structure adapted to China road and driving habits of users.Based on the durability development work of a own-brand car,the paper carries out the research on the durability of automobile body based on real vehicle road spectrum,proposes a development system from the durability condition,road spectrum acquisition,material testing,structural analysis to whole vehicle durability experiment.It has important guidance and reference siginificance to promote the competitiveness of independent brand product merchantability and reliability.Based on whole vehicle and suspension parameters a multiple dof vibration model of whole vehicle is established,through frequency response analysis between suspension and body forces,it is obtained that the sprung mass,suspension stiffness and damping parameters are the main factors influencing suspension force.Then,based on whole vehicle and suspension parameters of one independent brand car,a complete vehicle dynamic model is established.Both front and rear suspension model are calibrated by simulation and experiment of K&C performance,the complete vehicle dynamic model is calibrated by simulation and experiment comparison of vehicle handing stability and bump ride comfort performance.The dynamic model is driving on the D class random road,it is to analysis the influence law of suspension and body force when the suspension stiffness,shock absorber damper and sprung mass change.It is concluded that these parameters have important influence on body and suspension force again.The dynamic load of body and suspension is the main factor influencing the fatigue life of car body,and it can provide important ideas for the anti fatigue performance of the vehicle body by analyzing the law of the influence of the parameters of the whole vehicle and the suspension.Based on road spectrum collection,the paper makes the research on damage equivalent relation between user road and proving ground test,and makes the research on caculation method of load spectrum based on multi-body dynamic model.First of all,it is to collect the national road spectrum sampling and proving ground road spectrum,to compare the acceleration variation of frequency distribution and damage statistical.The study shows that the proving ground road spectrum and user road spectrum is high correlation and quite equivalent damage.It introduces the pretreatment technology which include to filter original load spectrum,deburing,drift correction of data gathered.Based on wheel six component input,a fixed body and half constraint body dynamic load calculation model are estabished to study the load spectrum calculation.Studies shows that the calculation method of the two solutions is almost identical to the load distribution characteristics,and the joint force between body and suspension body by half body constraint method is less burr and relatively optimal.Finally,the half body constraint method is verified high accuracy by comparing simulation with test of some classic driving condition,it could provide accurate and reliable load input for the next durability simulation of automobile body structure.A fine body finite element model is established,and calibrated by simulation and test of the inherent characteristics of body structure.First of all,the method of building finite element of body is introduced,because of complicated geometric characteristics of BIW,to deal with detailed holes,rounded corners,ribs,fillet weld,spot weld,edge,viscose connection and bolt connection details.Based on the above method,the finite element method of large body about three hundrad sixty thousand element is completed.Then,through the tests of the mode bend stiffness and torsional stiffness test of body,comparing test result with simulation,the comprasion error is with five percent.So,the accuracy of the finite element model of body is high enough to be used for prediction of fatigue life.In view of the complex working condition and load,the life prediction and optimization of body structure and spot weld are carried out.First of all,it introduce the method of multiaxial fatigue analysis and analysis flow,and carries out the testing of fatigue performance of vehicle body materails,and to prepare for the fatigue life analysis.According to the characteristics of vehicle body motion and load input,the method of inertia release is selected and combined with load spectrum to predict the fatigue life of body structure.The prediction results show that the joint area of front subframe and the body has lowest fatigue life but meet the request.At the same time,the fatigue life of body spot weld around the rear left shock absorber is the lowest,just meet the request of low margin.Therefore,under the constraint local mount stiffness and stress,the local topology optimization is carried out to get new distribution of spot weld in order to improve the fatigue life of spot life,and obtain better effect.Finally,in order to verify the optimization of the body to meet the durability requirements,the proving ground and indoor bench test is put into practice.First of all,the proving ground durability test is introduced,and the method of the bench test by loading iteration from the road spectrum to bench load spectrum.The above two test results show that the fatigue life of automobile can meet the design target.The paper establishes a development system from the road spectrum collection,load calculation,material durability testing,body structure fatigue prediction method,proving ground and bench test to verify the integration of the fatigue life,and provides the feasible and practical value for the design of fatigue durability of the vehicle in the process of development.