Study On The Residual Life Of Couples For Railway Heavy Load Vehicles

China's heavy haul railway transportation has been developing continuously in the past 40 years since the reform and opening up: the weight of train formation has increased from 3500 tons to 10,000 tons,20,000 tons and 30,000 tons.With the increase of traction weight and running speed of trains,the longitudinal load of trains increases continuously.As a key component of transmitting longitudinal force,fatigue cracks are common in the main load-bearing structures(hook tongue and hook body)of couplers during operation.In this paper,the residual life of the coupler of heavy haul freight cars after cracks occur is studied,which provides a method reference for the maintenance rules,structural design and safety evaluation of the coupler.Firstly,through the full investigation of Shenhua railway line,freight car type and marshalling,coupler retardation system and maintenance technology,the data of repair failure and replacement record of coupler in HMIS(H Management Information System)system are obtained.On the basis of statistics and analysis,the main failure form of coupler is identified as crack caused by structural fatigue failure.The location and cause of crack rate are also discussed.Secondly,according to the actual stress situation of coupler,the material non-linearity and contact non-linearity finite element model considering the assembly relationship of coupler is established.Quasi-static calculation results show that the stress of the coupler body and the root of the coupler tongue traction platform is larger,which coincides with the position where the crack frequency of coupler is higher in actual use.The calculation results show that the strain zone of coupler tongue simulated by finite element method coincides with the actual compression zone of couple The rationality and validity of the simulation model are proved.At the same time,based on the results of the structure and stress nephogram of the traction platform,the reason why the stress at the root of the traction platform on the hook body is larger than that at the bottom of the traction platform is analyzed,which indicates that the manufacturing technology and structure of the coupler have certain room for improvement.Then,according to the measured longitudinal load time history of the coupler on Shenhuang Line(Daliuta-Shenchi South-Huanghua Port)of 10,000-ton marshalling train,the load spectrum of the coupler in grade 19 of finite element simulation and bench test is compiled by means of rain flow counting and average force correction.The crack initiation life of the coupler is calculated by local stress-strain method,and the 16 H coupler tongue(corresponding to type 17 coupler body)is calculated.)The crack initiation life of the roots of the upper traction platform is the shortest,which is about 1.36 million kilometers.Considering the casting defects of the coupler and the accidental damage during service,the determination of the crack initiation life of the coupler should be conservatively corrected according to the actual situation in the field.Finally,based on the theory of fracture mechanics,the crack propagation process and residual life of hook tongue and hook body are simulated.Based on the maximum tensile stress as the principle of determining the direction of crack propagation,the multi-load stress intensity factor averaging theory is used to introduce the 19-stage load spectrum of coupler,and the corresponding relationship between the crack propagation of coupler tongue and coupler body and the service mileage is established.The minimum allowable dimensions of unstable propagation of the root crack of the traction platform under coupler tongue and the root crack of the traction platform under coupler body within 400,000 km are determined,which are 17.44 mm and 5 mm,respectively.The influence of load and material fracture toughness on crack propagation and structural instability is studied.When the load increases to 1500 kN or the material fracture toughness is lower than 3100 MPa.?mm,the residual life of the structure will be seriously reduced.The method of evaluating the residual life of couplers of railway freight cars proposed in this paper provides a theoretical basis and engineering application basis for the maintenance regulations,structural design and safety evaluation of couplers.