Research On The Effect Of Wheel Polygon On The Fatigue Crack Initiation Life Of W1-type Fastening Clip Used In The High-speed Railway

With the increase of traffic density of high-speed railway,the improvement of train running speed and the aging of vehicle track components,the phenomenon of wheel polygon is not uncommon,which will cause the strong wheel-rail impact,seriously affecting the service life of the components of vehicles and rails.In recent years,some lines have appeared the phenomenon of fracture failure of the fastening clip caused by wheel polygon.As a key component of the fastening system,the fastening clip plays an important role in adjusting the rail direction and providing longitudinal resistance.Once the fastening clip fails,it will cause serious consequences.In order to study the fatigue properties of W1-type fastening clip under the influence of wheel polygon,firstly,three conditions were proposed on the basis of the fatigue test specification of the fastening clip,which were conducted in the indoor fatigue test of W1-type fastening clip on the fatigue test machine.Secondly,according to the design drawings and physical installation of the fatigue test,the finite element model of the fatigue test was established to extract the stress/strain spectrum of the nodes of the maximal stress places of the W1-type fastening clip under three conditions,on which the fatigue life was calculated by using the uniaxial and multi-axis fatigue criteria respectively.Then the most accurate and reliable fatigue criterion was selected by comparing with the fatigue test life.Finally,a dynamic model of vehicle-rail vertical coupling including wheel polygon was established to obtain the vertical acceleration and the vertical movement of the rail,which were used as inputs to the finite element model of W1-type fastening clip of WJ-8 fastening system.Then the stress/strain spectrum of W1-type fastening clip was obtained from the model,which was used to analyze the fatigue characteristics of the clip.The main conclusions were as follows:(1)The deflection kept unchanged and only the dynamic displacement range increased of W1-type fastening clip(condition 1),the clip failed when the fatigue cycle count was257,712,and the fracture position was near the back bend of the outer arm of the clip;the dynamic displacement range maintained unchanged and the deflection increased of W1-type fastening clip(condition 2),the clip failed when the fatigue cycle count was 1,147,152,and the fracture position was near the middle limb;the deflection and dynamic displacement range of W1-type fastening clip simultaneously increased(condition 3),the clip failed when the fatigue cycle count was 215,441,and the fracture position was near the posterior bend of the outer arm of the clip.(2)Using uniaxial and multi-axis fatigue life criteria to calculate the fatigue life of W1-type fastening clip,compared with the fatigue test life,it was found that the calculation results of the FS criterion were close to the fatigue test results: the fatigue life of condition 1 was233,151,the fatigue life of condition 2 was 1,010,644,and the fatigue life of condition 3 was187,899,and the fracture position was very close to the fatigue test.(3)Using the FS criterion to analyze the fatigue spectrum of W1-type fastening clip obtained by vertical displacement of the rail,the fatigue life of the clip was much greater than5 million,which was difficult to explain the premature fracture failure phenomenon of the clip due to the wheel polygon.(4)Using the FS criterion to analyze the fatigue spectrum of W1-type fastening clip obtained by vertical acceleration and displacement of the rail,the fatigue life of the clip decreased sharply with the increase of the amplitude of the wheel polygon.When the amplitude of wheel polygon was less than 0.010 mm,the fatigue life of the W1-type fastening clip was much greater than 5 million;when the amplitude of wheel polygon was 0.015 mm,the fatigue life of the clip was 1.092 million;and when the amplitude was increased to 0.020 mm,the fatigue life of the clip dropped sharply to 365,049.(5)The angle of fracture plane of the W1-type fastening clip at the amplitude of 0.015 mm was different from the amplitude of 0.020 mm.When the amplitude of wheel polygon was 0.015 mm,the θ angle and the φ angle were 99,178;while the θ angle and the φ angle were 105,178 when the amplitude of wheel polygon was 0.020 mm.