Fatigue Analysis of Railway Wheels Under Combined Thermal and Mechanical Loads

Abstract

Nowadays, the railway vehicles are widely used in many countries as one of the most important transportation systems. Nucleation and growth of fatigue cracks in railway wheels stem from different factors such as wheel-rail rolling contact, thermal loads between wheel-rail and wheel-brake block created in braking process, presence of structural defects in wheel material, and so forth. Also, increasing speed and axle loads of wheels aggravates these factors. These cracks can reduce wheel life and even in severe cases derailment may occur. Therefore, the thermo-mechanical fatigue problem of wheels is a very important issue as is doing an accurate mechanical and thermal analysis of the investigation and estimation of fatigue life of wheels, and also, the prediction of crack behavior under thermo-mechanical loads is necessary. In this article, stress fields created by combined thermal and mechanical loads in railway wheels is investigated. Thermal stresses are usually created as a result of frictional heating produced by applying brake shoes on the wheel tread and also as a result of the occurrence of slip between wheel and rail at the braking stage. The obtained results confirm the important effects of thermal loads on stress fields and fatigue life of wheels. In this article, thermal loads are determined by modeling the contact of the rail-wheel and two brake blocks and by identifying heat partition factors and friction coefficient between these components. One of the other advantages of the presented work is modeling of wheel rotation, while in many of the similar investigations either this rolling is not modeled or its effect is simplified as translating pressure distribution along the rail-wheel contact region. The use of a 3D FE analysis for determination of rail-wheel contact pressure instead of Hertz contact theory is also noteworthy.