| High-speed turnout is the key railway equipment to ensure the safety and stability of train operation.Because of the large scale and fast speed of high-speed railway construction in China,the research on fatigue cracks of turnouts is insufficient,which results in the centralization of vertical cracks of straight-switch rails at high-speed turnouts of early-opened high-speed railway lines,intensifies the interaction between vehicles and turnouts,shortens the service life of rail components,and increases the maintenance investment.In this paper,the mechanism of longitudinal horizontal fatigue cracks in straight-tip rail is revealed by the systematic study of wheel-rail stress analysis,fatigue crack initiation and fatigue crack propagation.The main work and conclusions are as follows:1.Based on the theory of static analysis,the mechanical properties of straight-tip rail under various working conditions were systematically studied,and the mechanism of fatigue crack was revealed from the point of view of stress and strain.In this paper,the finite element analysis model will be established by using the measured profile data in situ,and the static performance analysis will be carried out by using linear reduction integral.The ideal linear hardening elastic-plastic model is used for the constitutive relationship of materials.The results show that,compared with the original design profile,after excessive grinding of working edge arc of turnout straight-tip rail,the contact points between straight-tip rail and wheel with fatigue cracks measured in situ move towards non-working edge,the contact stress amplitude of contact spot increases obviously,and the internal stress,plastic stress and shear stress amplitude of straight-tip rail increase somewhat.It is concluded that the increase of equivalent stress and horizontal shear stress in the range of 2-10 mm below the top surface of non-working side rail of straight-switch rail results in the initiation and propagation of longitudinal horizontal cracks of straight-switch rail.2.Based on the theory of fatigue analysis,the fatigue performance of rail heat treatment materials under train cyclic load was studied,and the fatigue life was predicted.The local stress-strain method is used to analyze the fatigue model.Brown Miller criterion is used to judge the fatigue crack.Mean stress formula is used to modify the fatigue model.Medians(steels)method is used to estimate the fatigue parameters.Miner linear cumulative damage theory is used to analyze the influencing factors of longitudinal fatigue crack initiation of straight-tip rail.The results show that the fatigue life decreases firstly and then increases with the increase of section width of straight-switch rail of heat treatment material.Compared with the original design profile,the crack initiation life of turnout straight-switch rail decreases after excessive arc grinding,so the excessive grinding should be avoided as far as possible in turnout area.3.Based on the theory of fracture mechanics,the fatigue crack growth of straight-tip rail under train cyclic loading is studied,and the relationship between fatigue crack growth period and crack depth is studied.Pairs formula is used in the fracture analysis model.The stress intensity factors of all crack front joints are calculated by reading the stress analysis results.The influence factors of longitudinal fatigue crack growth of straight-tip rail are analyzed.The results show that the angle,length and location of the initial crack will affect the crack growth rate in the process of fatigue crack growth analysis.Horizontal cracks on non-working side present ?-? type composite cracks.When the tip width of the straight-tip rail is small,the maximum contact stress is concentrated on the non-working side,which increases the possibility of fatigue cracks on the non-working side of the straight-tip rail.4.Based on the analysis of the influencing factors of fatigue crack initiation and propagation of straight-tip rail,different optimization control measures are put forward,and the feasibility and treatment effect of different schemes are studied.The fatigue crack development of straight-tip rail can be effectively reduced by reducing the friction coefficient of wheel-rail contact surface.For the design section,the non-working side reverse R=5mm arc scheme is recommended to prevent the crack of non-working side of switch rail;for the non-injured and injured section on site,the switch rail profile grinding scheme is recommended to repair the switch rail;for the switch rail with more serious damage on site,it is suggested that the downtrack be carried out to avoid further deterioration of the disease and endanger the safety of driving according to wheel-rail contact stress analysis. |
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