Research On Fatigue Test Method And Key Technology Of Railway Freight Car Body

The fatigue reliability research of key components has been greatly improved by the support of simulation and testing methods with the development of heavy haul and fast technology in railway rolling stocks,which has become an effective support for the development of new freight wagons,however,the physical full scale freight wagon structural fatigue method,at present,has been mainly used in evaluation of the simulations and on-track dynamics tests for the limit of immature theory,complicated testing method,high testing cost and lack of testing facilities.In addition,the practical result of the popularly used nominal stress method shall obviously affected by the appearance of non-consistent stress calculation or stress testing and the subjective selection of the S-N curve,therefore,the intensive study in theory&method and testing&simulation aimed at the effectiveness of car body fatigue life evaluation shall surely make great contribution to the development of heavy haul and fast technology in railway industry.The full scale freight car fatigue and vibration test rig in China has become the foundation and precondition of car body full scale fatigue testing research and a good way for the development of new fatigue simulation methods.Based on the said background,the paper presents the car body fatigue testing method and key technologies,as well as introduction of large system simulation and the latest structural stress method,aimed at solving the fatigue life prediction problem of car body,and the relevant works are detailed as follows:(1)Research on fatigue test method of full scale railway freight car body has been carried out.Through analyzing the dynamic equation of running conditions of car body on actual tracks,researches on the basic principle of realizing track simulation on test rig are carried out.On the basis of this principle,on the one hand,data compression method of multi-channel constant amplitude domain was introduced for the researches on acceleration test on car body fatigue;on the other hand,selective researches on track simulation target are carried out;thus drive signals of actuator can be calculated through iteration with the car body acceleration speed signal as target.Under the premise of consistent fatigue damages on the location to be evaluated,this method can better simulate the time domain process and car body damaging process more appropriately,compared with the traditional body bolster acceleration speed integrative approach.(2)Through researches on fatigue test method of full scale railway freight car body,test procedure requirements of car body fatigue test are put forwards,and key technologies involved in the tests are discussed.Through the dynamic response test of C70E gondola wagon,researches on data processing,data compression and drive documents,finally the fatigue test on C70E car body is completed.The test results are consistent with the actual operation situations of C70E wagons,thus can verify the rationality and applicability of the car body fatigue test method.(3)Considering the limits of test sample,number of measuring points and costs on actual tests,firstly researches on wagon(loaded with bulk cargos)modeling are carried out based on large system simulation modeling method,according to the mechanical characteristics of the fatigue test rig.And the flexible body modeling method of gondola wagon loaded with bulk cargos is put forward.Then considering the consistency of boundary conditions between simulation and actual tests,the simulated model of fatigue test rig frame is introduced into the simulation calculations,and forms multi-body rigid-flexible coupling dynamics theoretical model.The modifications of dynamic parameters of the system are completed with the drive documents as simulated model inputs,through comparisons between simulations and tests.Through these researches,the vibration conditions of the fatigue test rig are consists with simulation of the stress states of car body and test results.Therefore,it’s obvious that the system simulation model with the combination of rigid fatigue test rig frame and the flexible car body is more suitable for bench test simulations and can provide more accurate loadings for carrying out fatigue evaluation on the car body.(4)Researches on car body fatigue simulations are carried out in two parts.In the first part,test drive documents from Beijing to Chengdu are selected as inputs for bench simulation model.Center plate load,side bearer load and coupler load are extracted.Uni-dimensional spectrum is formed using rain-flow counting.Then fatigue evaluation on critical welds is carried out using structural stress method.(5)In the second part,with respect to fatigue problems if car body weld defects,I(r)l/m equation is deduced,and life estimation method including defects is established.The typical welded structure with defects and draft-bolster structure with defects are used to carry out tests and comparison calculations.Simulations results of both parts are consistent with respective test results.Researches on this method lay solid foundation for further realizing the integration of structural stress method and virtual car body fatigue test rig in the future.The service of the car body fatigue and complete wagon vibration test rig provides the requisite condition for further investigations in the field,meanwhile,the relevant researches in car body fatigue test method and virtual simulation method proposed the core theory for car body fatigue evaluation test,identified the rationality of the simulations,and realized the communications between physical test and simulations.The further investigation in structural stress evaluation method made proper compensation to welding structural fatigue method and improved the accuracy of fatigue calculations.In conclusion,the research in this paper starts from the physical engineering activities,with the guidance of proper theory,by the integration of physical test and simulations,to achieve a series of useful reference,which shall certainly provide good examples for the development of new rolling stocks and establishment of perfect fatigue reliability evaluation system.