Railway Wheel Tread Research Articles

A finite element thermomechanical analysis of the development of wheel polygonal wear

Polygonal wear is a type of damage commonly observed on the railway wheel tread. It induces wheel-rail impacts and consequent train/track components failure. This study presents a finite element (FE) thermomechanical wheel-rail contact model, which is able to cope with the three possible generation and development mechanisms of polygonal wear: initial defects, thermal effect, and structural dynamics. The polygonal wear-induced impact contact and further development of wear are simulated. The simulated elastic contact solutions are verified against the program CONTACT. Different material properties (elastic, elasto-plastic and elasto-plastic-thermo, i.e. with thermal softening) and initial polygonal profiles are then applied to the FE model to investigate the influence of wheel/rail material and wear amplitude on wheel-rail contact stress and wear development. The simulations indicate that the wheel-rail impact-induced temperature may reach up to 362 ℃ at the contact interface, and the high temperature at the contact area influences wheel-rail contact stress and wear depth.

Influence of Axle Weight and Frequency on the Tribological Properties of Laser-Repaired 316L Stainless Steel Coatings in Railway Wheel Tread Braking

The impact of the complex braking environment on the service performance of the repair fusion cladding was studied, which is of great significance to improve the ability of the train wheel track system to resist the extremely harsh environment. In this paper, a 316L stainless steel coating was prepared using laser fusion cladding repair technology for the local damage location of the train wheel tread. The MS-HT1000 high-temperature wear tester was used for the experiment. Then, the influence of different braking conditions on the friction and wear performance of the repaired specimens at room temperature and high temperature was analyzed. The results showed that the microstructure of the laser-repaired 316L stainless steel coating was dendritic and eutectic, and its physical phase was mainly composed of austenite, Fe-Cr, and carbides. The wear rate increases with the rise in the shaft weight load, indicating that the higher the contact load, the more severe the wear. In contrast, the influence of the friction coefficient in a room temperature environment is less variable. With an increase in the braking frequency, the wear of the specimen firstly rises and then decreases, and when the frequency is 1 Hz, the value of the wear rate at room temperature is the largest, and the wear surface appears as more peeling layers, and a large amount of wear debris is randomly distributed, which manifests as the wear mechanism being characterized by abrasive wear and adhesive wear. Therefore, different factors affect the wear level of the material differently, with the axle weight load having the greatest influence. The relevant results help to provide corresponding theoretical references for the optimization of parameters under the braking condition of the wheel tread, which ensures the normal operation of the braking system when driving.

Influence of railway wheel tread damage on wheel–rail impact loads and the durability of wheelsets

Dynamic wheel–rail contact forces induced by a severe form of wheel tread damage have been measured by a wheel impact load detector during full-scale field tests at different vehicle speeds. Based on laser scanning, the measured three-dimensional damage geometry is employed in simulations of dynamic vehicle–track interaction to calibrate and verify a simulation model. The relation between the magnitude of the impact load and various operational parameters, such as vehicle speed, lateral position of wheel–rail contact, track stiffness and position of impact within a sleeper bay, is investigated. The calibrated model is later employed in simulations featuring other forms of tread damage; their effects on impact load and subsequent fatigue impact on bearings, wheel webs and subsurface initiated rolling contact fatigue of the wheel tread are assessed. The results quantify the effects of wheel tread defects and are valuable in a shift towards condition-based maintenance of running gear, and for general assessment of the severity of different types of railway wheel tread damage.

High-temperature tribological properties of coatings repaired by laser additive manufacturing on railway wheel tread damage

Heavy-duty train wheels can easily cause local damage. Laser additive manufacturing technology has obvious advantages in repairing local damage to train wheels. The high temperature sliding condition caused by tread braking is a severe test for the coating of damaged wheels repaired by laser additive. In this study, three self-fluxing alloy powders, Fe-, Ni-, and Co-based, which are the most widely used in laser cladding, were selected as repair materials. The sliding friction wear performance at high temperatures was evaluated with an HT-1000 ball-disk wear tester, and the wear mechanisms of the repair area, substrate, and counterpart surfaces of the specimens were analyzed. The results show that the microstructure of the coating after the surface damage of the wheel is repaired by laser additive is mainly composed of dendritic structure and eutectic structure. Compared with the base material, the hardness of Fe-, Ni-, and Co-based alloy cladding coatings is significantly improved. At the same time, the wear resistance of the repaired wheel steel samples was improved to different degrees. The wear mechanism of the repaired area of the Fe-based alloy sample is mainly adhesive wear, and the wear mechanism of the repaired area of the Ni-based alloy sample is adhesive wear and oxidation wear. However, the surface of the wear scar of the Co-based alloy repaired sample is relatively smooth, the damage is slight, and the friction reduction effect is the best.

Fuzzy Logic-Based Identification of Railway Wheelset Conicity Using Multiple Model Approach

The deterioration of railway wheel tread causes unexpected breakdowns with increasing risk of operational failure leading to higher maintenance costs. The timely detection of wheel faults, such as wheel flats and false flanges, leading to varying conicity levels, helps network operators schedule maintenance before a fault occurs in reality. This study proposes a multiple model-based novel technique for the detection of railway wheelset conicity. The proposed idea is based on an indirect method to identify the actual conicity condition by analyzing the lateral acceleration of the wheelset. It in fact incorporates a combination of multiple Kalman filters, tuned on a particular conicity level, and a fuzzy logic identification system. The difference between the actual conicity and its estimated version from the filters is calculated, which provides the foundation for further processing. After preprocessing the residuals, a fuzzy inference system is used that identifies the actual conicity of the wheelset by assessing the normalized rms values from the residuals of each filter. The proposed idea was validated by simulation studies to endorse its efficacy.

Railway wheel tread damage and axle bending stress – Instrumented wheelset measurements and numerical simulations

ABSTRACT A combination of instrumented wheelset measurements and numerical simulations of axle bending stresses is used to investigate the consequences of evolving rolling contact fatigue (RCF) damage on a passenger train wheelset. In a field test campaign, stresses have been monitored using a wheelset with four strain gauges mounted on the axle, while the evolution of wheel tread damage (out-of-roundness) has been measured on regular occasions. The strain signals are post-processed in real time and stress variations are computed. Based on a convolution integral approach, the measured wheel out-of-roundness has been used as input to numerical simulations of vertical dynamic wheelset–track interaction and axle stresses. Simulated and measured axle stresses are compared for cases involving combinations of low or high levels of rail roughness and the measured levels of RCF damage. The study enhances the understanding of how wheel tread damage and track quality influence axle stress amplitudes.

ANALYSIS OF RAIL-WHEEL INTERACTION IN CURVES WITH SMALL RADII

Purpose. The authors goal is to point out that the new geometric design of the curves of tramways is recommended, furthermore the introduction of a new parameter too. This new parameter is the Creepage Index (CI), which takes into consideration the values of wheel creep from the optimal rolling radii difference on every wheelset in the bogie. Methodology. The several types of railprofiles and railway wheel tread profile geometres have been analised with a special softver and compared with standards, TSIs and BOStrab. Findings. The result of the analisys is that the mechanical conformity of rail/wheel interaction (running characteristic) in tramway tracks are unfavourable and new regulations are necessary to reduce the rail/wheel wear and corrugation especially in curves with small radii. Originality. In the EU the Technical Specifications for Interoperability (TSI) are in force, which regulate the parameters of running behaviour for the international and national public railways. However, the regulation does not apply to domestic tramways. In the course of the analysis, the author propose to introduce a system of regulation, which based on the mechanical suitability of the rail/wheel interaction. This is especially justified, because for example the regulation of German light rails (BOStrab) only requires the geometric dimensions of the wheel and the groove of the rail and their limits. Practical value. The author developed new geometric design and limit systems of narrow curves and straight tracks and a new test parameter, which shows degree of coherence for running characteristic of the given curve and vehicle, from the aspect of infrastructure, in case of all wheelsets of bogie. This CI (Creepage Index) parameter takes into account all wheel creep values resulting from the variations (+, –) of the optimum rolling radius difference. This results the tightening of bogie design principles and for running characteristic reasons, it requires the continous flange running of the outer wheel in narrow curves.

In-Service Detection and Quantification of Railway Wheel Flat by the Reflective Optical Position Sensor.

Railway wheel tread flat is one of the main faults of railway wheels, which brings great harm to the safety of vehicle operation. In order to detect wheel flats dynamically and quantitatively when trains are running at high speed, a new wheel flat detection system based on the self-developed reflective optical position sensor is demonstrated in this paper. In this system, two sensors were mounted along each rail to measure the wheel-rail impact force of the entire circumference by detecting the displacement of the collimated laser spot. In order to establish a quantitative relationship between the sensor signal and the wheel flat length, a vehicle-track coupling dynamics analysis model was developed using the finite element method and multi-body dynamics method. The effects of train speed, load, wheel flat lengths, as well as the impact positions on impact forces were simulated and evaluated, and the measured data can be normalized according to the simulation results. The system was assessed through simulation and laboratory investigation, and real field tests were conducted to certify its validity and correctness. The system can determine the position of the flat wheel and can realize the quantification of the detected wheel flat, which has extensive application prospects.

Temperature-dependent wear of tread-braked railway wheels

The paper describes the results of brake dynamometer experiments conducted to evaluate the influence of the tread temperature caused by tread braking on the wear rate of railway wheel tread. Employing a full-scale tread brake dynamometer composed of a brake block, a wheel, and a railwheel, wheel-rail rolling contact was imposed on the wheel tread surface heated under several braking scenarios. In dynamometer tests simulating the braking patterns of an actual vehicle exposed to unexpected hollow tread wear, no tread wear was observed after repetitive station stop braking, whereas tread wear was observed only for the rolling contact region after repetitive holding braking for load cases in which the internal tread temperature reached 300 °C. The wear rate of the rolling contact region was determined for various temperatures by performing experiments in which rolling contact was imposed at a constant tread temperature. The wear rate of the wheel tread increased rapidly with temperature at the tread surface for internal temperatures of 200 °C–300 °C. The wear volume obtained in the experiment was converted and generalized to determine the temperature dependence of the wear rate of the wheel tread as a function of the travel distance. The surface temperature of the tread and the internal temperature distribution were computed by FEM. The maximum temperature on the tread surface was estimated to range from 240 °C to 380 °C. The hollow wear of tread-braked railway wheels is primarily attributed to plastic deformation of the tread surface caused by hot rolling, i.e., rolling under a softened state with an increased temperature of the wheel steel on the tread surface. Verification of thermally activated process using Arrhenius equation confirms this conclusion.

Инновационные технологии машиностроения, обеспечивающие повышение долговечности железнодорожных колес и рельсов

In the paper it is shown that railway wheels and rails life depends considerably upon wear-resistance of their tread working surfaces. There is presented an innovation technology of a railway wheel tread electromechanical processing allowing the increase of its life. The innovation technology of railway wheel working tread electromechanical processing allowing its life increase is shown. The innovation technology for rail working tread allowing its life increase is given.

A methodology to predict thermomechanical cracking of railway wheel treads: From experiments to numerical predictions

In the present study, thermomechanical cracking of railway wheel treads is studied by full-scale brake rig tests and finite element simulations. The main goal of the paper is to perform thermomechanical rolling contact fatigue life predictions. The wheel tread material is subjected to simultaneous mechanical and thermal loads due to rolling contact and stop braking, respectively. Full-scale tests featuring three series of repeated stop braking cases have been performed in a brake rig featuring a tread braked wheel that is in rolling contact with a so-called rail-wheel. The brake rig test conditions have been simulated numerically using the finite element method where the effect of “hot bands” on the tread is accounted for as indicated by the experimental findings. Stresses induced by temperature from braking as well as tractive rolling contact loading on the tread are considered. The mechanical response of the wheel material ER7 is obtained from a plastic Chaboche material model calibrated against data from cyclic experiments at room temperature and up to 625°C. Finally, a strategy for prediction of fatigue life with respect to ratchetting failure is discussed.

The competitive role of wear and RCF: Full scale experimental assessment of artificial and natural defects in railway wheel treads

Assessments of the severity of wheels tread defects under rolling contact fatigue conditions are in general very uncertain when based on theoretical concepts supported only by small scale material characterization and without the possibility of a full scale validation. In real service conditions, the tread surface and subsurface defects are subject to a number of variable mechanical loading conditions given by the combination of vertical and lateral loads and wheelset steering. The present paper describes some interesting experiences from recent RCF tests performed by Lucchini RS on its full scale roller rig (named “BU300”) on two very high speed railway wheelsets coming from revenue trafic. The test rig was used in order to reproduce running conditions very near to normal service conditions. A concept for test acceleration was applied: the ratio curve distance/straight distance was increased, since curves are more critical to RCF compared to straight running. Firstly, the scope of the test was to monitor the behavior of defects in order to evaluate the impact on the safe integrity and to reduce RCF damage by considering two different steel grades: ER8 (EN13262) and Superlos® developed by LucchiniRS. Secondly the results of the tests provided interesting information regarding rate of crack propagation.Depending on the crack depth from the tread surface and the wear rate obtained, an important basis for describing the competitive role of RCF and wear is offered. In addition some considerations on preventive wheel reprofiling (skimming) strategies are proposed that can reduce RCF impact on wheel life. The accumulated results are also valuable since they can be used as a basis for the validation of RCF models. Finally this work confirms the ability of the roller rig to reproduce equivalent service running conditions that can generate RCF cracks similar to those found in service.

Thermal cracking of railway wheels: Towards experimental validation

Thermal cracking of railway wheel treads is investigated using a combined experimental and numerical approach. Results from controlled brake rig tests of repeated stop braking cycles for a railway wheel in rolling contact with a so-called railwheel are presented. Test conditions are then numerically analysed using finite element (FE) simulations that account for the thermomechanical loading of the wheel tread. For the studied stop braking case, thermal cracks are found in the wheel tread after few brake cycles. Results from thermal imaging reveal a frictionally excited thermoelastic instability phenomenon called “banding” where the contact between brake block and wheel occurs only over a fraction of the block width. This condition results in locally high temperatures. The numerical analysis assesses ratcheting response of the wheel tread material under operational conditions corresponding to two types of banding patterns and also a case of uniform heating. Fatigue life predictions are estimated from the evaluated ratcheting response using a simplified accumulation rule. Predicted lives are found to be in reasonable agreement with experimental results.

Development of Test Stand Prototype for Rail Vehicles Brake Components Testing

The paper deals with the new RAILBCOT test stand building reasons explanation. A project features definition is described. There is possible to perform the railway wheel tread profiles wear research under the rail vehicle in operation conditions simulation. This simulation is possible to execute on the test bench. An important feature of the research is the equivalent conicity change analysis. The paper outlines the stand operation principles a main structure components design and components parameters specification, the tests control, data acquisition and data assessment.

Influence of Short Thermal Cracks on the Material Behaviour of a Railway Wheel Subjected to Repeated Rolling

An analysis of whether and how the occurrence of shallow (radial) thermal cracks promotes additional plastic deformation of a mechanically loaded wheel tread is carried out. The study employs numerical simulations of a 2D slice of an elastoplastic railway wheel tread containing thermal (radial) cracks. The cracked wheel material is subjected to repeated passes of a frictional rolling contact load. The effect of the existing thermal cracks on bulk deformation and subsequent rolling contact promoted growth is quantified. Results indicate that thermal cracks of a depth of 0.1 mm have a negligible effect, whereas 1.0 mm cracks significantly decrease the bulk resistance of the wheel material. Further, it is shown how the magnitude of stress, strain and deformation depends on the direction of applied traction.

Thermal cracking of a railway wheel tread due to tread braking–critical crack sizes and in fluence of repeated thermal cycles

A numerical study of tread cracking due to thermal loading induced by tread braking is carried out. The analysis features a computationally efficient approach combining two-dimensional finite-element simulations with an analytical evaluation of resulting stress intensity factors. The analysis identifies critical sizes for when existing surface cracks are prone to propagate under thermal loading and resulting crack lengths after propagation. The results imply that fully functional brake systems are not likely to induce thermal crack propagation under normal stop braking, but that with pre-existing defects, a severe drag braking due to malfunctioning brakes may cause very deep cracking. Furthermore, the analysis concludes the cracking to be a static phenomenon related to the most severe brake cycle, i.e. later brake cycles of similar or lower severity will not cause any significant propagation of existing cracks. Additional three-dimensional finite-element simulations are used to validate the model, and they indicate two-dimensional results to be on the conservative side. This paper originated from the 2011 IHHA Conference.

Railway wheel and rail head profiles development based on the geometric characteristics shapes

Abstract The proposed contribution deals with the methods for the railway wheel and rail head profiles development on the base of the intended shape of wheelset/track contact geometric characteristics. The profiles creation method through arcs radii profile variation is explained, as well as the emphasis is directed to the “Iterative method for a railway wheel tread profile design”. This method is explained in a more detailed way in the article. The base for the creation of new profiles with the help of the first method is an interactive attitude based on the modification of the original shape which is defined by section of a railway wheel profile, with interconnected and exactly defined arcs radii. It is possible to change them, according to shape needs of the final geometrical characteristics. The base of the iterative method, which is of the highest importance in this article, is to develop a new profile under given conditions – a prescribed shape of the contact points distribution and the shape of Delta-r function. The newly developed wheel profile in the couple with given rail profile will have the requested chosen characteristics shapes. This method can be after modification used for a design of rail profile in accordance to the wheel profile.

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.

Study on Rolling Contact Behaviors of Three Kinds of Railway Wheel Treads

The rolling contact behaviors between LMA, S1002 and XP55 wheelset and track in static rolling contact are analyzed using the rolling contact theory of three-dimensional elastic bodies with non-Hertz form and numerical program of CONTACT. The numerical results indicate that three kinds of wheel treads have different difference of rolling radius and equivalent taper. The rolling contact behaviors between three kinds of wheel treads and CHN60 rail have obvious difference. The comprehensive analysis indicates that the matching effect of LAM wheel tread and CHN60 rail is relatively superior. Furthermore, it is suggested that new wheel tread should be designed and optimized for the high-speed railway.

305 フラットはく離損傷機構解明のための接触応力場解析(機械材料・材料加工I)

305 フラットはく離損傷機構解明のための接触応力場解析(機械材料・材料加工I)