DYNAMIC ANALYSIS OF RAIL WHEEL STRUCTURE DUE TO DEFECTS

Abstract

The railway is the major transport facility in India. With the increase in globalization, there is a need to increase the load bearing capacity and speed. The increase in performance of railway vehicle needs proper maintenance and detection of defects in time. To avoid accidents and derailment, there is a requirement to have proper understanding of the causes of defects and failure. Any defect or imperfection on any component may cause instability and discomfort and even can leads to derailment. Railway is the most energy efficient, safe, and economic overland movers of passengers and heavy freight. Rail wheels are the basic components of railway vehicles, which is not only provide the support to the entire vehicle but also guides the train and carry the heavy load. Generally, due to braking or jamming of brakes the wheel skids over rails and material removal took place from the tread. This frequent skidding removes large amount of metal from the surface known as wheel-flat defect. In this work, the wheel with a flat defect is modeled. The analysis has been performed for finding natural frequency and dynamic stress of the wheel surface and the effects of the contact force for both types of wheelflat defect. The wheel-rail is modeled as a mass-spring-damper system to simulate the basic wheel–rail dynamics. The nonlinear behaviour is analyzed and instantaneous dependence of contact stresses on several structural and dynamic parameters. Railway wheel fails due to fatigue for long run. When the wheelflat defect occurs on the wheel, creates high stresses and high impact forces. The model of the wheel with ―flat‖ defect has been analyzed using FEA and a subsurface crack in the vicinity of the defect is studied. The wheelflat is modeled on the wheel circumference in the ABAQUS software. The study of wheelflat is done by obtaining the contact forces and stresses around the wheel flat especially taking the material both elastic and elastic-plastic. Due to rolling contact fatigue the subsurface crack propagates and removes large material from the tread. The subsurface crack can originate in the vicinity due to presence of cavity or inclusion may leads to fatal accidents, in absence of early detection of flat detection. Stress intensity factor has been obtained for the crack propagation due to subsurface crack by taking wheel material as elastic. The above work is extended to the analysis of wheelflat and a subsurface crack in the beneath is studied using FEA by considering Elastic-Plastic Material. In this study, wheel material is taken as Elastic-plastic and the factor for crack propagation i.e. J-Integral factor has been obtained. Generally, wheel fails due to fatigue for long run. The stress generated is repeated for large number of cycles, which leads to fatigue. The conventional wheels have been designed for large number of load cycle but are overweight. For long run wheel, wear occurs and the fatigue causes catastrophic failure. In this work, the response surface method is being used to find out the fatigue life equation by taking load and dimension of wheel as variable. The natural frequency is taken as a factor for fatigue life. An ANOVA analysis has been done and formulation of function for natural frequency is obtained. An objective function has been formulated for minimization of mass of railway wheel considering the strength and geometrical constraint. Railway wheelset is directly influenced by vehicle dynamics. The mathematical model for single railway wheelset is employed to research the nonlinear dynamics of the railway wheelset. Here, during this process the concentration is on creep forces and suspension parameters, which are nonlinear. For finding stability of the wheelset, an elaborate research on the lateral stability and yaw stability of one wheelset has been performed. The whole analysis is done numerically and the critical velocity is find out for tangent track case. For this analysis, Indian railway parameters of freight wagon are taken and stability of empty wagon is studied. The results using Hertzian-Kalker Model (HKM) are compared with the Heuristic Creep Model (HCM)analysis. The average speed of wagon is 40-50 km/hr for empty wagons, which is facing huge hunting problem. The numerical model is consisted of a whole wagon with two conventional three-piece bogie running on wheelsets. The wheel-rail contact is considered with a nonlinear Heuristic Creep Model (HCM)for both single point and two point contact. Coulomb friction model is also considered for contact between the truck and bolster. The present study concentrates on the critical hunting, which is mainly depending on primary and secondary suspension parameters. A numerical study is done using MATLAB to obtain optimum parameters for increasing critical speed so as to stabilize wagon for both increased speed and at loaded vehicle.