Investigation on fatigue life of Rail-Wheel assembly using Finite Element Analysis
In recent years, the axle loads on railway cars is increasing due to increased transport of the goods and faster infrastructural growth. The rail wheels are subjected to high contact stresses of alternating magnitude due to rolling action of the wheels under these loads. The rail wheels should be able to sustain these variable loading for reasonably infinite life. Accidents due to fracture of rail wheels affects the safety of railway facility. Therefore more attention is paid to the quality of rail-wheel. The rail wheels are found to fail predominantly due to fatigue under these variable loadings whereas other modes of failure are damage to railway bogie, suspension failure and in some cases derailment of the vehicle. After all the advancements in design, materials and non-destructive inspection, the fatigue propagation and failure due to damage of railway components remains an important issue for safety engineering in railways. In this work, an attempt is made to investigate the occurrence of stresses in rail-wheel assembly due to high contact loads at the assembly points. The study involves the determination of equivalent stress (von-Mises), strain, safety factor using finite element method on ANSYS® 2016. An appropriate understanding of these mechanisms needs in depth knowledge of physical interactions between rail and wheel. The rail wheel assembly is assumed to operate under the designed load. The Goodman mean stress correction theory is used to obtain results. The results on the fatigue life are presented which are assumed to depend on these factors.
A model for rolling contact failure
Abstract Rolling contact stress and failure analyses were conducted for the Hadfield steel (manganese steel) and the Bainitic alloy (J7). The first alloy is used in diamond crossings and frogs in the railroad industry while the second alloy is a candidate for such applications. A series of fatigue experiments were conducted on these alloys to establish the damage parameters. The proposed fatigue damage parameter incorporated the role of both shear and normal stress ranges on the `critical' plane upon surveying all planes at a material point. Maximum local plastic strains, accumulated strains, and three-dimensional residual stresses were computed under pure rolling conditions for p o / k (Hertzian pressure normalized by yield stress in shear) values in the range 4.0 to 8.0 using a semi-analytical approach. A multiaxial stress–strain plasticity model developed by the authors was used in the calculations of the contact stress and strain fields. The advantage of this model over the previous models is that it predicts the correct trends in the material ratchetting rate and non-proportional loading response. For life prediction, a new combined ratchetting–multiaxial fatigue damage model was presented. The damage at different depths below the surface was interrogated with this model to determine the location where failure will originate. The results show that the Bainitic alloy exhibits longer lives under the same Hertzian pressure and for both materials the life is finite when the normalized pressure, p o / k ratio, exceeded 4.0.
Analysis of internal cracks in railway wheels under experimentally determined pressure distributions
Abstract In recent years much effort has been devoted to the definition of design approaches of railway systems based on the analysis of the system itself and on accurate knowledge of its effective working conditions. In this paper, the attention is focused on railway wheels. This latter component is subjected to different types of damage: sub-surface crack propagation is considered. The prediction of the evolution of this process depends on the knowledge of the stress intensity factors concerning modes I, II and III, which are dependant both on the total load acting on the wheel and on how the load is transmitted through the wheel/rail interface. However, until now the solutions commonly used consider a theoretical (Hertzian) pressure distribution, even if, due to wear or to the dynamic phenomena, the actual contact patch can be strongly different for most of the lifespan of the wheel. An approach is developed with the aim to solve the case of an internally cracked wheel subjected to an arbitrary contact patch and pressure distribution. It is based on Boussinesq's formulae and utilises a three-dimensional finite element model of the part of the wheel close to the crack to calculate the stress intensity factors along a curvilinear crack front. Pressure distributions experimentally determined by means of a technique based on the reflection of high-frequency ultrasonic waves from the wheel–rail interface were applied to internal cracks in wheels: the results were critically compared with the those obtained by considering Hertzian pressure distributions, the aim being the assessment of the influence of the contact conditions in respect of damage cause by internal crack propagation.