Parisa Hosseini Tehrani

Curved tracks and certain conditions may result in two-point contact, in which the rail experiences a multiaxial stress state. The initiation and propagation of subsurface cracks follow this. Studying these cracks is crucial for railway safety. In this work, a validated finite element model of the rail and wheel, developed using the weight function method and half-space modeling, is applied to study the three modes of stress intensity factors (SIFs). The equivalent SIF is also extracted to assess 3D subsurface elliptical cracks. The principle of LEFM is applied to obtain the variation of SIFs of subsurface cracks along their fronts. In the rail, three areas have been selected for analysis. Two of these areas are located in the head, and one is located in the web of the rail. The objective of this study is twofold. First, the SIFs of subsurface cracks will be assessed under two-point contact conditions. Second, the lateral load resulting from the effect of passage in a curve, in conjunction with a vertical load, will be examined. Different subsurface crack arrangements and angles are compared to determine the critical state. The outcomes indicated that 45-degree and horizontal cracks have higher stress intensity factors. In the gauge area, the nearly horizontal subsurface crack exhibits the largest equivalent stress intensity factor compared to all other conditions. This makes the zone more susceptible to failure in the curved tracks.

Dynamic modeling of wheel-rail interaction is significant in accurate fatigue analysis of railways. Both location and magnitude of the contact stresses in the contact area must be evaluated accurately and efficiently via computational tools. In curved railway tracks, the distribution of the force exerted on the wheel is complex as it is multiaxial rather than uniaxial; thus, a more comprehensive computational model is required. In this work, a numerical procedure is developed to investigate the fatigue crack initiation on the curved tracks. The Universal Mechanism software is used to specify the spectrum of axial wheel force as input to a three-dimensional explicit finite element model to obtain the resulting stresses at the wheel-rail contact region. A critical element with the maximum von Mises stress value is treated as the element where the fatigue crack is most probably to be initiated. In this element, the critical plane method is used to determine the orientation of the crack initiation. The effect of the radius and slip ratio on the exact site of fatigue crack initiation is established in this approach, and the contact point influence on the fatigue crack initiation parameter is investigated. The proposed model successfully predicts a practical wheel-rail dynamic response to cyclic loading, applying the geometry of the curved track.

The roughness effects on the wheel-rail contact problem is an essential topic. In this paper, a new analytical-numerical model has considered assessing the specifications of a rough surface contact problem. The new model includes asperities and strain hardening effects together. Consideration of these assumptions is more realistic in comparison to similar simplified works. In this work, the effects of material properties variation on a contact problem realize. Besides, considering the strain hardening effects, the contact results for wheel-rail material are obtained. The contact characteristics variations versus separation, such as contact force, contact stiffness, and contact area, are shown in semilogarithmic diagrams considering different surface roughnesses and hardening parameters. The new model results show the significant influence of the assumed hypothesis on the contact characteristics.

Wheel-rail contact in railway engineering is an important topic. Due to different materials and surface roughness of wheel and rail, the contact characteristics can alter significantly. This article aims to investigate the effects of surface roughness and asperities on the contact parameters such as contact area, contact force, and contact stiffness. The lateral contacts between asperities are assumed to be the general contact condition. Azimuthal and contact angles distributions are assumed to be spherical harmonic distribution. This assumption is compatible with the asperity distribution on the wheel and the rail surfaces. Besides, a new combined model is developed to cover the stick-slip and the plasticity effects in contacting asperities. The results of the presented model offer very good estimations for the asperities contact characteristics, especially at the small-contact area and separation where high-contact pressure and plastic deformation usually exist.

One of the main reasons for mechanical failures in railway structures is attributed to the propagation of defects and cracks. Exact prediction of crack growth in rails and wheels may lead to solutions to reduce damages, improve efficiency and facilit

In this task, a numerical study is utilized to determine the residual stress of the flash butt joint in the UIC60 rail. To accurately predict critical locations of tensile residual stress, the influence of phase transformation is considered in the simulation. To reduce the possibility of failure in the welded rail, the most effective parameters of the flash butt welding during and after the process are optimized to decrease critical tensile residual stresses in the weldment. To this end, a coupled procedure by considering the imperialist competitive algorithm (ICA) in Matlab and process modeling in the Python code of Abaqus software is performed. In this procedure, time duration and heat input at each step and upsetting force are considered as welding machine parameters, and the cooling rate is assumed as post welding factor. Using the effectiveness of the ICA method, in nonlinear and huge multi parameters and steps problems, the optimum values of considered factors in terms of reducing the tensile residual stress in butt joint are obtained. The optimum values and effectiveness of each controlling parameter on the maximum and the pattern of tensile residual stress to diminish the failure of the butt welded rail under service loads are discussed.

Continuously welded rails are widely used in the Iran railway network, which are generally built using the flash-butt welding process. To accurately model the flash-butt welding process, thermal analysis, and prediction of the welding residual stresses, the influence of upsetting force on the total electrical resistance and a material model with consideration of the influence of temperature on the material properties are included in the numerical modeling. In this paper, numerical and experimental studies, including the finite element method, thermography, metallography, and hardness testing are performed to determine the characteristics of the welded UIC60 rail. By studying the fractured flash-butt welded UIC60 rails, it is shown that the location of the crack initiation and the rail failure in the web and heat affected zone of the welded rails was similar as compared to the maximum tensile residual stress calculated by numerical simulation. According to the numerical and experimental results, it is shown that four key parameters – such as the maximum temperature during the welding process, the total welding time, the upsetting time, and the upsetting force – control the size, microstructure, and the hardness profile of the heat affected zone which directly affects the characteristics and quality of welding.