Study On Rail Corrugation

Rail corrugation is one of the most serious problems in railway engineering. The phenomena of rail corrugation has been observed and studied for over 100 years. Although much progress on the recognition of the mechanisms of initial corrugation formation and development has been made with theoretical and experimental methods, the studies on corrugation have not explained the mechanism of its initial formation perfectly, and have not formulated a united and validated mathematical model to explain the initial formation mechanism and the factors affecting the evolution of rail corrugation so far. With increases of train speed, axle load, traffic density and the introduction of new vehicles, etc., the phenomenon of rail corrugation shows a tendency to increase. Therefore a great deal of money is spent every year by railway transportation companies on the maintenance and replacement of corrugated and broken rails. The railway transportation security is directly endangered. Rail corrugation causes fierce vibrations of the structures of both railway vehicle and track, noise, discomfort for passengers and residents living near the tracks, damage for goods and reduction of the use life of structural parts. Therefore studies on rail corrugation are very important from the practical and cognitive points of view.Supported by the Natural Science Foundation Committee of China (Nos. 59935100, 50375129 and 50575188), the Foundation of Ph.D. Student Education of Education Ministry of China (No.20020613001) and the Special Foundation for Excellent Ph.D. Thesis, the main research work in the present dissertation involves:(1) The studies on rail corrugation in the past and now in the world are reviewed. The significance and research orientation of rail corrugation are indicated.(2) A rail corrugation calculation model due to wear mechanism is established, which considers a combination of Kalker's non-Hertzian rolling contact theory to be modified, a rail material wear model and a vertical and lateral coupling dynamics of half a passenger car and a curved track. A corresponding numerical program is developed. The corrugation model is more completed and complicated as compared with other ones appeared in published papers. The developednumerical program can consider a feedback process not only between the rail wear and the transient coupling dynamics of one wheel and the curved track, but also between the rail wear and the transient coupling dynamics of four wheels of a same bogie and the curved track. The effect of rail defects on the formation and development of rail corrugation is investigated in detail. A lot of numerical results are obtained. Theses results help understand the mechanism of corrugation initiation and development and settle the corrugation problem. The corrugation model is validated by experiment using a full-scale test facility. The test results are in good agreement with the numerical results.(3) Most of previous stress analyses of rolling contact assumed a constant normal pressure. The current work presents a two-dimensional elastic-plastic finite element model of non-steady state rolling contact. The general cyclic material behavior including cyclic strain ratcheting and stress relaxation that occur under rolling contact is taken into account. The effects of different conditions of pure rolling contact, full slip and partial slip rolling contact and multiple step loading on residual stresses and strains are considered. The developments of rolling contact stresses, strains and deformations are obtained for repeated rolling contact. The results indicate that studies of rolling contact fatigue and the initiation and development mechanism of surface corrugation or ripple should take non-steady state and cyclic strain ratcheting effect into consideration.(4) A rail corrugation calculation model due to plastic deformation is established, which considers a combination of Carter's two-dimensional rolling contact theory, the elastic-plastic finite element model of non-steady state rolling contact and a vertical dynamics model of one quarter of a car coupled with a curved track. The model involves a concept of feedback between the uneven running surface plastic deformation and the contact vibration of wheel and track. The ratcheting effect of rail material under repeated rolling contact and the effect of residual deformation accumulation on corrugation are considered. The formation and development of rail corrugation due to plastic deformation under non-steady state loading are studied. The influence of a scratch on rail on the initiation and evolution of the plastic deformation induced rail corrugation is investigated. The evolution rule of an initial corrugation with an increase of car passage is analyzed. Detailed material performances under the trough and crestsuch as stresses, strains and plastic flow rate are obtained.(5) According to field survey and statistical analysis of the number of damage rails, the phenomena of rail squashing and cracks in rail joint region are one of the main problems in heavy haul lines and mountainous lines in China. The rail joint is always an origin of the initiation and development of rail corrugation. In this thesis, three-dimensional nonlinear finite element dynamic analysis code ANSYS/LS-DYNA3D is used to establish an elastic-plastic finite element model of three-dimensional contact and impact of wheel and rail. Mutibody contact problem is taken into consideration in the model. The wheel-rail contact-impact process during the wheel running over the rail gap is simulated. The distribution of stresses and strains in the jointed rail head are given. The influences of axle load, train speed, yield stress and tangent modulus of rail material on the stresses and strains are investigated in detail. The study would provide a method and useful datum for further research on the mechanism of impacting damage on railhead at jointed rails and improving the rail joint mode.