Jieling Xiao

Comparison of calculation methods for wheel–switch rail normal and tangential contact

Wheel–rail contact is more complex in railway a turnout than in ordinary track and, thus, necessitates an advanced model to simulate dynamic interaction and predict rail wear. The main aim of the present work is to assess the application of several wheel–rail rolling contact models in railway turnout. For normal contact problems, wheel–rail contact models based on four different methods are compared: Hertz theory, the semi-Hertzian method, CONTACT, and the finite element method. The assessment is based on the results of contact patch shape and size and contact pressure for several wheelset lateral displacements. The load is set to a constant and equal to static wheel load. Calculations are performed at the section of switch rail head with width 35 mm in CN60-1100-1:18 turnout; both standard and worn rail profiles are accounted for. For tangential contact problems, four corresponding methods are assessed, based on the calculation of creep forces, distribution of the stick/slide region and computational efficiency: Shen–Hedrick–Elkins theory, FASTSIM, improved FASTSIM based on semi-Hertzian method, and CONTACT. It is found that the normal contact problems solved by the semi-Hertzian method and CONTACT correlate well with the finite element method, and the tangential contact problems solved by improved FASTSIM and CONTACT are quite favorable. The conclusions of this work can provide some guidance for contact model selection in the dynamic simulation and wear prediction of railway turnout.

Bridge-Rail Interaction for Continuous Welded Rail on Cable-Stayed Bridge due to Temperature Change

Continuous welded rail (CWR) has been used in high-speed railways in China. The bridge-rail interaction caused by temperature change when CWR is paved on cable-stayed bridges is studied in this paper. A bridge-rail interaction model is first established using the finite element method. Based on the formulated model, the variation pattern of the force and displacement of rail and bridge-rail relative displacement due to temperature change is studied. The additional temperature forces experienced by stay cables and main towers are obtained, and the influence of the stiffness and temperature change of stay cables and main towers on the additional temperature force of rail is studied. Two simplified algorithms are proposed to facilitate the analysis of bridge-rail interaction. Results show that the distribution patterns of the additional temperature force and displacement of rail on the cable-stayed bridge are the same as those on a common bridge, and the forces experienced by stay cables and main towers are within the safety limit of bridge components. The stiffness variation of stay cables has more influence on the bridge-rail interaction than that of main towers. The distribution patterns of the forces and displacements obtained by the simplified algorithms are similar with those obtained by the FEM. The simplified algorithms can be used for the design of CWR laid on cable-stayed bridges.

Dynamic Response of Wheel-Rail Interaction at Rail Weld in High-Speed Railway

As a main part of continuously welded rail track, rail weld widely exists in high-speed railway. However, short-wave irregularities can easily initiate and develop in rail weld due to the limitation of welding technology and thus rail weld has been a main high-frequency excitation and is responsible for deterioration of track components. This work reports a 3D finite element model of wheel-rail rolling contact which can simulate dynamic wheel-rail interaction at arbitrary contact geometry up to 400 km/h. This model is employed to investigate dynamic response of wheel-rail interaction at theoretical and measured rail weld, including wheel-rail force and axle-box acceleration. These simulation results, combined with Quality Index (QI) method, are used to develop a quantitative expression, which can be easily applied for evaluating rail weld deterioration based on measured rail profiles and axle-box acceleration.

Image Detection System and its Application for Dynamic Wheel/Rail Contact in High Speed Railway

Dynamic wheel/rail contact is the core connecting link between vehicle and track under high speed running condition. Based on optical technology, photoelectric technology, digital image processing techniques and software engineering, a image detection system for dynamic wheel/rail contact is developed. This system is used to get the distribution law of wheel/rail contact points on rail head and wheel tread under high speed running condition. High-speed cameras are placed at the rail’s inside and outside. When the train passes the test zone at high-speed, the wheel/rail dynamic contact image can be obtained. A complete wheel/rail contact space trace and contact state are also obtained through process of image feature recognition. The system consists of such hardware as camera imaging and optical unit, image acquisition and storage devices, lighting sources, trigger unit and a image processing software. There is a key step in image acquisition and processing. Image with distortion is restored by the distortion correction function for distortion-free images. Then according to the markers information of calibration parameter, inside and outside part of the corrected image is stitched to form a complete image of wheel/rail contact. This system is verified by laboratory test assembly and field measurement. It can accurately collect clear wheel/rail contact image and qualitatively present the wheel/rail contact state. It can also provide the wheel and rail contour curve and the wheel/rail normal distance of each section. This has provided data support and visual reference for the further study on wheel/rail contact state of high-speed railway.Copyright