Study On Crack Propagation Life Of Heavy Haul Freight Car Coupler Knuckle

Since the reform and opening-up,China’s heavy haul railway has developed rapidly,and the weight of train formation has increased from 3500 tons to 10,000 tons,20,000 tons and30,000 tons.The coupler knuckle,as the main force transmission part of the coupler,bears most of the longitudinal load.With the increase of the traction weight,its service conditions gradually deteriorate,reducing the service life of the coupler knuckle and increasing the probability of cracks.Therefore,combining with the actual application conditions of the knuckle,this thesis studies the crack propagation life of the knuckle,which provides a theoretical basis for extending the service life of the knuckle and formulating a reasonable maintenance cycle.Firstly,taking the actual measured load of the 10,000 tons train on the Shenhua line as an example,this thesis carried out a study on the method for compiling the longitudinal load spectrum of the coupler.Taking the actual line conditions and the marshalling form of the train as input,a simulation of the longitudinal load of 10,000 tons of couplers was carried out and a load spectrum was compiled.Based on the equal damage principle,the total damage under the load spectrum is compared with the measured results of the line,and the reliability of the simulation results of coupler longitudinal load and the simulation model of train longitudinal dynamics is verified.On this basis,the simulation of the longitudinal load of the 20,000 tons marshalling coupler on the Shenhua line was carried out and the corresponding load spectrum is compiled to provide load input for the fatigue bench test and crack propagation simulation of the coupler.Secondly,a statistical analysis was carried out on the failure mode of the coupler knuckle,and it was found that the crack rate of the traction platform under the knuckle was as high as68%.The finite element model of the assembly coupler consistent with the line form was used for simulation,and there is a large difference between simulation and the result of investigation and research.Therefore,the coupler knuckle stress test and coupler force analysis were carried out to modify the simulation model.Meanwhile,the modified single coupler finite element model was more consistent with the survey results and the test results.Hence,the single coupler finite element model was used as the basis for crack propagation calculations.Thirdly,based on the sub-model of the coupler knuckle with three-dimensional cracks,the relationship between the length of the crack and the running mileage of the different parts of the coupler knuckle was calculated.The critical safety dimensions of the bottom traction platform and S-plane cracks are 55 mm and 90 mm respectively,and the corresponding crack propagation life is 480,000 km and 528,000 km respectively.In order to verify the reliability of the simulation results,this thesis performed the fatigue crack growth test of the coupler knuckle,and compared the simulation results with the test results.As shown by the results,the safe running mileage of the bottom traction platform and the S-plane is between 95%～99%and 99%～99.9% of the survival rate of test fracture respectively,and the crack variation rule calculated by simulation is close to the test average value,and the simulation results have a high reliability.Finally,from the two aspects of optimizing the load distribution of traction platform and reducing the stress concentration,the method of reducing the height of the bottom traction platform,increasing the fillet of the root of the traction platform,and increasing the wall thickness of the S-plane is used to improve the structure of the coupler knuckle.After the improvement,the crack propagation life of the bottom traction platform and the S-plane is increased by 17.1% and 23.7% respectively.