Study On Derailment Theory Of Switch Aera In Small Number Turnouts Based On Wheel-Rail Relationship

Since turnouts are weak points of the railway lines,wheel/rail relationship in the turnouts is more complicated than the section line,which makes the safety concern of the turnout area more aware of.In particular,the small number turnout is more serious than the turnout in the section line and high speed railway,because of its laying conditions and maintenance status.The vehicle derailment accidents occur more frequently at small number turnouts.In this paper,on the basis of reviwing the research status of vehicle derailment theory,the rail/wheel contact model and theory of derailment at the switch area of small number turnout is studied.The main contributions of this paper are as follows:1.Study on the wheel/rail contact relation in the switch area.Through the analysis of switch rail head plane cutting process,the relationship between design parameters such as the plane line and the cutting path of the switch rail head is derived.The calculation method of the three-dimensional profile of switch rail and the composite profile of the switch rail and stock rail is established.Accuracy of the method proposed in this paper is verified by comparison with the commonly used profile interpolation approach.For the complex wheel/rail contact state of the switch area,by dividing the switch area into different sections,all possible situations of wheel/rail contact in the switch area are described in detail.On the basis of the trace method,the problem of multi-point contact solving in the switch area is solved by dividing the region of the wheel.Based on the above results,geometry calculation program of wheel/rail contact in the switch area is developed,which can be used in both static and quasi-static analysis of the contact state between wheel and rail,and can be used as a submodulus in wheel/rail dynamics system simulation.2.Study on the theory of derailment under quasi-static condition.In this paper,the 3D wheelset derailment analyzing model has been established,and the calculation framework of thresholds for derailment coefficient and wheel load reduction coefficient are derived.Theoretically and experimentally,the difference of the calculation results based on different contact model such as Shen-Hedrick-Elkins creep model,Polach creep model and Fastsim simplified creep model were compared.Finally,Shen-Hedrick-Elkins creep model is chosen.The influence on the threshold of derailment coefficient and wheel load reduction of attack angle,friction coefficient,maximum wheel/rail contact angle and static wheel weight was investigated with the framework.3.Study on the limit value of running safety in the switch area under quasi-static condition.This paper analyzed the geometrical contact relationship in the process of derailment at different sections of the switch area with the framework derived above.It is found out that,there may be two climbing processes during the derailment of the wheel in the switch area.And according to the results of the contact geometry,the safety limits of derailment of the switch area for 2d and 3d conditions are studied.4.Study on dynamic derailment behavior of wheelset in Switch AreaThe model of elastic positioning wheelset for dynamic derailment analysis in switch area has been established.The method of solving the vertical relative displacement of wheel-rail is used to solve the normal elastic compression of wheel-rail,so that the judgment of wheel-rail contact and separation state is realized,which is more suitable for the simulation analysis of wheelset dynamic derailment.The dynamic derailment behavior of the wheelset passing through the switch is simulated.The results show that,when the wheelset facing move in deverging line,the wheel can easily climb the switch rail within the range of 5mm ~ 20 mm width of the switch rail.While when the wheelset trailing move in deverging line,the process of climbing rail is completed on the stock rail.As a result,the risk of derailment when wheelset facing move in deverging line is significantly higher than that of wheelset trailing move in deverging line,special attention should be given to prevent derailment occurs when the wheelset facing move in deverging line in the switch.5.The technology of improving safety at switch area of small number turnoutThe threshold of running safety at switch area in small number turnout is compared with the current staqndard for threshold of running safety in China.It shows that,the current limit of vehicle safety evaluation index in our country is not suitable within the range of 5mm ~ 15 mm width of the switch rail in switch area.Considering that it is unrealistic to set a special evaluation index limit for switch area in small number turnout,the technical route to enhance the traffic safety at switch area of small number turnout is established from two aspects,and the N0.5 turnout is taken as an example to carry out the related research.