Fatigue Life Prediction And Structure Optimization Of Heavy-haul Frog

Heavy-haul railway in our country was based on the development of ordinary railway,on which the train caused seriously damage to turnout structure.Now switches cannot meet requirements of existing or under construction heavy-haul railway lines in China.As the significant turning area of rail vehicles,failure problems of heavy frog were notable.In this thesis,it was not only studied the heavy-haul frog at different section by finite element simulation and structure optimization,but also the optimization effects of heavy-haul frog fatigue performance by different types of wing rail or switch,and different material strength.The fatigue performance of heavy-haul frog was analyzed by three methods of fatigue life analysis,strain fatigue analysis and crack propagation life analysis,combined experimental researches with finite element simulations.The wing rail was structural optimized to improve the fatigue life of heavy-haul frog.Low carbon alloy steel can obtain uniform bainite organization after heat treatment process of slow cooling from 870 ℃and tempering at 300 ℃.The fatigue fracture mechanism of test materials was surface crack initiation,which was typical ductile fracture with its fractures showed characteristic dimples and fatigue striations.The standard 75 kg/m-12 heavy frog,only at the point rail top width of 10 mm and 20 mm were two-point contact between the wheel and rails,while at the other point rail top widths were one-point contact.The maximum contact stress showed the biggest value in the 20 mm section and the smallest value in the 55 mm section.The fatigue life distribution of fatigue life analysis and the stress distribution of static analysis showed same regular pattern at same cross section.The maximum stress point and minimum life points were located near the contact spot.The strain fatigue life were higher than the stress fatigue life on all sections.Optimization of the wing rail by cutting work side 5 mm and moving 5 mm to the point rail and elevating its top surface,made the contact sections of rail top surface width of 10 mm,20 mm,30 mm,40 mm at two-point contact.The optimization effectively reduced the maximum stress at the rail top surface width of 20 mm and 40 mm contact sections,and the maximum stress at 40 mm was below the yield strength.The optimization can reduce the maximum contact stress and prolong the fatigue life of the heavy frog,which applied to 75 kg/m wing rail but not to 60 kg/m wing rail.And the optimization applied to different materials and different switch types.The plastic toughness can be increased by properly decreasing yield point,tensile strength and yield ratio,thus the maximum contact stress and minimum life of different cross-section for frog tended to converge,otherwise tended to disperse.The fatigue properties of bainite steel can be improved by reducing yield ratio with changing the content of C and ratio of trace elements.