Anders Ekberg

Anisotropy and rolling contact fatigue of railway wheels

Abstract Modes of rolling contact fatigue failure are described and categorized for railway wheel treads and rims. The overall strength and endurance of railway wheels is investigated with special focus on material anisotropy and fatigue characteristics. An improved metallurgical design of the wheel material is proposed and tested. A procedure for defect-tolerant design of the wheel, addressing anisotropic fatigue properties, is outlined.

Fatigue initiation in railway wheels—a numerical study of the influence of defects

Stresses around a material defect in the rim of a railway wheel are studied during sequences of over-rolling contacts using elasto-plastic finite element analysis. Results in the form of animations show a complex evolution of the stress field. Based on multi-parametric studies, conclusions of practical interest to railway engineers are drawn. Insights into the physical process have been gained.

Rolling contact fatigue of railway wheels—a parametric study

Abstract With the increase of speeds and axle-loads in railway transportation, the fatigue life of the wheels has become an important issue with respect to economy and safety. A deeper understanding of the fatigue mechanisms and a better prediction of lifetimes should be of interest to both manufacturers and operators. In this paper, a refined equivalent-stress criterion is developed and is implemented in a previously described fatigue life model (A. Ekberg, H. Bjarnehed and R. Lunden, A fatigue life model for general rolling contact with application to wheel/rail damage. Fatigue Fract. Eng. Mater. Struct. 18 (10) (1995) 1189–1199). The influence of some important parameters on the fatigue life is evaluated using the improved model. The parameters varied are vertical wheel load, diameter of wheel, radius of railhead, residual stresses, and longitudinal and transverse contact stresses. The validity of the model and the consequences of the results are discussed. Finally, the possibility of using simplified equivalent-stress criteria in order to decrease the required computational efforts is discussed.

Prediction of Dynamic Train-Track Interaction and Subsequent Material Deterioration in the Presence of Insulated Rail Joints

Numerical analysis of high-frequency dynamic train–track interaction is combined with the analysis of material deterioration in terms of rolling contact fatigue (RCF) and plastic deformations to analyze the influence of insulated rail joints. These joints form local rail irregularities and lead to a local change of dynamic track stiffness. Dynamic responses at wheel passes are evaluated. Further, related plastic deformations at the joint and increased RCF impact along a stretch of the track adjacent to the joint are predicted.

Influence of Short-Pitch Wheel/Rail Corrugation on Rolling Contact Fatigue of Railway Wheels

Abstract A numerical procedure to integrate simulation of high-frequency dynamic train-track interaction and prediction of rolling contact fatigue (RCF) impact is presented. Features of the included models and possibilities of applications are outlined. The influence of short-pitch rail corrugation and wheel out-of-roundness (OOR) on RCF of a high-speed passenger train is investigated. It is shown how the corrugation and the OOR will have a profound effect in that levels of wheel and rail irregularities that have been measured in the field may be sufficient to generate subsurface-initiated RCF. In particular, the high-frequency content of the contact forces is of importance. Errors induced by neglecting such high-frequency components in measurements and/or simulations are investigated by comparing RCF indices based on contact forces that have been low-pass filtered with various cut-off frequencies. To avoid cracking due to RCF, a maximum roughness level in the wavelength interval up to 10 cm is sought. To limit the effects of corrugation, grinding practices have been altered leading to a significant decrease in RCF.

Effects of imperfections on fatigue initiation in railway wheels

Abstract The paper begins with a description of three observed types of fatigue failure. It continues with a discussion on fatigue mechanisms and numerical modelling of rolling contact fatigue, especially in the presence of material defects. Based on this discussion, the main mechanisms behind the three types of failure are analysed from a mechanical point of view. Finally, practical implications of the results in this paper are discussed and some suggestions of means of preventing fatigue failure of railway wheels are put forward. Future research areas are indicated.

Numerical Study of the Mechanical Deterioration of Insulated Rail Joints

Abstract Numerical simulations are performed to study plastic deformation and fatigue impact of an insulated joint. The simulations feature a sophisticated constitutive model capable of capturing ratcheting under multi-axial loading conditions. Calculation results are presented in the form of effective strain magnitudes, plastic zone sizes, and multi-axial low cycle fatigue parameters. The simulation results indicate that the main damage mechanism at insulated joints is ratcheting and not low cycle fatigue. A parametric study quantifies effects of increased vertical and longitudinal load magnitudes, as well as the effect of an increased insulating gap. In particular, longitudinal loading is indicated as being severely deteriorating for the rail in the vicinity of the joint. Finally, the effect of rail edge bevelling is assessed and found to be small for the case studied.

Fretting fatigue of railway axles—a Review of predictive methods and an outline of a finite element model

Abstract The primary aim of this study is to investigate possibilities and difficulties in a computer-based prediction of fretting fatigue of railway wheel-axle assemblies. The study sets out with a review of predictive models of fretting fatigue with an emphasis on computer-based numerical methods of relevance to wheel-axle assemblies. Based on the review, a finite element (FE)-based numerical framework to predict fretting fatigue of wheel-axle assemblies is outlined. The benefits and drawbacks of the approach are discussed.

Wheel Tread Damage: A Numerical Study of Railway Wheel Tread Plasticity Under Thermomechanical Loading

A numerical study is presented where the impact of simultaneous thermal and mechanical loading on a railway wheel tread, as imposed by braking and rolling contact, is reported. A comparison is made of two-dimensional (2D) and 3D finite-element simulations of the thermomechanical problem featuring a material model that accounts for thermal expansion and plastic deformations. It is found that 2D simulations give unrealistic predictions of plastic deformations. The 3D simulations demonstrate a significant influence of the thermal loading also in cases of rather moderate temperature increases. In particular, the combination of thermal loading and high traction is found to be very detrimental.

Predicting crack growth and risks of rail breaks due to wheel flat impacts in heavy haul operations

Abstract The risk for rail breaks is investigated from mechanical and statistical points of view with particular focus on the influence of impact loads from flatted wheels. For a presumed rail head crack geometry and rail temperature, the stochastic relation between the crack position along the rail and the wheel flat impact position results in a risk of fracture. In addition to the analysis of the risk for final fracture, rail crack growth is also studied. In particular, the contribution of wheel flat impacts on crack growth rates is quantified. The study takes the form of a dynamic load analysis that evaluates rail bending moments due to wheel flat impact. Then, a fracture mechanics analysis is employed to establish stress intensity factors for rail head cracks under bending and temperature loading. These analyses are then combined to give risks of rail breaks and to quantify crack growth rates for varying operational conditions.