Numerical Study Of Wheel-rail Rolling Contact

In the railway system,the train is supported and guided by wheel-rail rolling contact.Its traction and braking depends on the frictional force transmitted by wheel-rail interface.Therefore,the relationship between wheel and rail is the core of railway research,influencing the safety and quality of train operation,the generation of frictional wheel-rail noise and damage evolution of wheel-rail interface.Modeling the wheel-rail rolling contact behavior is one of the basic scientific problems within wheel-rail relationship research.In order to achieve low resistance of wheel-rail rolling contact,it chooses material of high stiffness,leading to small contact patch and high stress distribution.Up to now,it is a big challenge to capture wheel-rail rolling contact behavior by experiment technique.Developing accurate and reliable rolling contact mechanics model by analytical or numerical method is therefore the core of this problem.This dissertation firstly reviewed the establishment and development of wheel-rail rolling contact model,which was divided into three parts including the classical rolling contact theory,fast algorithms towards vehicle-track dynamics and wheel-rail damage modeling,and complicated problem study of wheel-rail rolling contact based on FE method.However,with the continuous development of high-speed railway,heavy haul railway and metro line,there is still some deficiencies for the mentioned three aspects,which motivates the author to finish this dissertation.Kalker's variational method and numerical code CONTACT is the most authoritative theory applied to steady rolling contact.However,there is still a difference between Kalker's theory and actual operational environment such as the conformal or curved rolling contact.In Chapter 2,it expanded and extended Kalker's variational method to 3D asymmetric and curved wheel-rail rolling contact,and coded corresponding numerical program CURVE.It analyzed the influence of 3D asymmetric geometry and curved surface characteristics on wheel-rail rolling contact,and provided a solid theoretical foundation for high efficient modeling of vehicle-track dynamics and wheel-rail rolling contact.Although Kalker's variational method can obtain accurate solution of wheel-rail rolling contact,it needs iteration.Such iteration nature limits high improvement of computational efficiency,and it needs to develop a more efficient simplified model.In Chapter 3,it compared the accuracy of several classical simplified models,and found the best non-elliptical adaptation approach for FASTSIM and Fa Strip applied to non-Hertzian rolling contact.For solving the accuracy problem of existed simplified algorithms on normal contact solution and its effect on traction bound,Chapter 4 proposed a new non-Hertzian normal contact model named INFCON,combined with Fa Strip and Ayasse-Chollet's local ellipse method for tangential contact.The validity and effectiveness of this model was validated by Kalker's CONTACT and compared against other simplified algorithms.It further proposed a strategy of hybrid contact modeling and suggested two geometric indexes for unify existed simplified algorithms to achieve higher efficient contact modeling.In order to drop basic assumptions of classical contact theory,Chapter 5 established a3 D vibration-rolling contact model of wheel-rail interaction using explicit FE method.This chapter described in detail the modeling approach,consideration of arbitrary geometrical irregularity,solving algorithm and post-process procedure.With this model,it solved quasi-static rolling contact solution under smoothed wheel-rail interface,and the model was validated via Kalker's CONTACT.It further applied this model to simulation of wheel-rail rolling contact on corrugated rail,and investigated the influence of varying friction coefficient on development of rail corrugation.For expanding the application of the FE model on wheel-rail rolling contact-impact behavior in presence of rail weld,it determined the quantitative relation among irregularity's geometrical gradient,wheel-rail impact force and axle box acceleration.It proposed two approaches for evaluating rail weld,with one for dynamic monitor based on axle box acceleration and the other for static detection based on geometry gradient measurement.These two approaches can provide an effective measure for the railway management on ensuring safety operation of high-speed train and reasonable maintenance of track.The three rolling contact models developed in this dissertation can fully cover the application field of wheel-rail rolling contact mechanics,providing an accurate and suitable numerical method for curved contact,vehicle-track coupled dynamics,interface damage prediction,dynamic wheel-rail contact mechanics and impact.