Simulation of contact-fatigue damage to rails in a welded rail joint area

Abstract

Introduction. The aim is to study the formation and accumulation of contact-fatigue damage in a welded rail joint area and to determine the degree of influence of the presence and deformation behaviour of the rail tread surface on an electrically welded joint on the occurrence and development of contact-fatigue damage, including the number of cycles to crack formation, which determines the service life of the welded joint.Materials and methods. In order to simulate the accumulation of contact-fatigue damage in the material surface under cyclical stress the authors take an approach that considers the peak values of the maximum shear stresses as an accumulation criterion. The following stages have been implemented as part of the given approach: determine the distribution of the probability density of wheel load on the rails; solve the contact problem of a rolling wheel considering the rail shape change in the collapse area; simulate the damage accumulation process.Results. The collapse of the rail material in a welded rail joint area causes, on the one hand, an additional dynamic load that increases the contact and internal stresses, and on the other hand, increases the contact area due to the flattening of the rail head, which reduces contact stresses. Depending on the depth of collapse, initial damage, nature of loading, the accumulation of contact-fatigue damage can both accelerate and slow down.Discussion and conclusion. It is confirmed that need for heat treatment to eliminate zones of reduced hardness in welded rail joint areas resulting in saddling, cracks and spalling. Reducing the weakened zone to the size of the contact spot will practically prevent the formation of impulse irregularities, and their formation upon contact would eliminate additional dynamic load. The problem may be solved by intensifying local heat treatment after welding, bandoning separate local heat treatment of rails after welding, and combining accelerated cooling of rail heads with the general welding process.

Keywords

• rail joint
• dynamic load
• contact problem
• contact-fatigue damage