Adam Bevan

The Influence of Wheel/Rail Contact Conditions on the Microstructure and Hardness of Railway Wheels

The susceptibility of railway wheels to wear and rolling contact fatigue damage is influenced by the properties of the wheel material. These are influenced by the steel composition, wheel manufacturing process, and thermal and mechanical loading during operation. The in-service properties therefore vary with depth below the surface and with position across the wheel tread. This paper discusses the stress history at the wheel/rail contact (derived from dynamic simulations) and observed variations in hardness and microstructure. It is shown that the hardness of an “in-service” wheel rim varies significantly, with three distinct effects. The underlying hardness trend with depth can be related to microstructural changes during manufacturing (proeutectoid ferrite fraction and pearlite lamellae spacing). The near-surface layer exhibits plastic flow and microstructural shear, especially in regions which experience high tangential forces when curving, with consequentially higher hardness values. Between 1 mm and 7 mm depth, the wheel/rail contacts cause stresses exceeding the material yield stress, leading to work hardening, without a macroscopic change in microstructure. These changes in material properties through the depth of the wheel rim would tend to increase the likelihood of crack initiation on wheels toward the end of their life. This correlates with observations from several train fleets.

Wheel surface damage: relating the position and angle of forces to the observed damage patterns

A new method of presenting simulated wheel/rail forces and relating these to the observed wheel damage has been developed. This indicates a good correlation between the predicted forces and the regions of the wheel where damage is observed in practice. There is also a good correlation between the angle of the predicted forces and the observed cracks. The angle evidence suggests that the dominant rolling contact fatigue cracks on the field side of the wheel tread are initiated by the occasional high forces when the opposite wheel is running in flange contact on sharp curves. Cracks may then be propagated by more frequent lower forces on moderate curves.

Optimisation of wheelset maintenance using whole-system cost modelling

The maintenance and renewal activities of wheelsets account for a large proportion of the whole-life costs for railway rolling stock. These activities are influenced by a large number of factors including depot constraints, wheel surface damage, fleet availability and vehicle design. If these factors are not managed efficiently it can have significant implications on a vehicle’s service provision, track damage, environmental and whole-life costs. Therefore, the development of an effective wheelset management tool will support the optimisation of maintenance and renewal regimes, thereby increasing wheelset life and reducing costs. Further development of the Vehicle Track Interaction Strategic Model has enhanced the rolling stock modelling capabilities of the tool through the development of the Wheelset Management Model (WMM). This model aims to assist in the strategic planning of wheelset maintenance and renewal activities and thereby allowing users to examine the benefits and cost impact of a range of different scenarios to optimise wheelset management strategies. This paper describes the capabilities of the WMM and illustrates how the model can be used to optimise a fleet’s maintenance strategy through the application of a realistic industry case study. The implications of different wheelset maintenance regimes on wheelset life and costs were examined. Finally, the paper presents how the tools can be used to investigate whole-system costs and demonstrate the impact of wheelset maintenance on track costs.

Use of railway wheel wear and damage predictions tools to improve maintenance efficiency through the use of economic tyre turning

This paper investigates the wear rate and pattern for wheels turned with thin flanges using economic tyre turning. Economic tyre turning refers to the process of turning wheels to a profile that has the same tread shape but a thinner flange than the design case profile, allowing less material to be removed from the wheel diameter during re-profiling. Modern wheel lathes are typically capable of turning such profiles but the GB railway group standards do not currently permit their use. The paper demonstrates how the wheel profile damage model (WPDM) can be used, with a good degree of accuracy, to predict both the magnitude of wheel wear and the worn profile shape of the design and economic tyre turning re-profiled wheels for service mileages exceeding 100,000 miles. The WPDM simulations were run for two typical electric multiple units (one suburban and one intercity train fleet) and a two-axle freight wagon. Additionally, it discusses the calibration methodology used to adjust the wear coefficients contained within the Archard wear model to improve the accuracy of the WPDM simulation results for specific routes and vehicle types. Furthermore, this paper presents the findings of a trial of economic tyre turning on a fleet of intercity trains. The analysis is extended to predict the effect of using economic tyre turning on rail rolling contact fatigue for typical routes and operating conditions using a series of vehicle dynamic simulations. The analysis considers new 56E1 and 60E2 rails together with a selection of worn wheel. The research provides valuable evidence to support a future change to the standards which will allow train operators/maintainers to implement economic tyre turning policies.

Judicious Selection of Available Rail Steels to Reduce Life Cycle Costs

The rate of rail degradation and hence its expected life is not uniform throughout any railway network and is governed by a combination of track, traffic and operating characteristics in addition to the metallurgical attributes of the rail steel. Consequently, it is suggested that any route or network is not a single linear asset but is a compilation of individual segments with different track characteristics, degradation rates and expected life spans. Thus, the choice of rail steel grade to maximise life (and minimise life-cycle costs) needs to combine knowledge of the metallurgical attributes of the available rail steels with the conditions prevailing at the wheel–rail and vehicle–track interfaces, whilst also considering the economic costs and benefits of the different options. This paper focuses on the classification of the susceptibility to rail degradation in various parts of a mixed-traffic network using vehicle dynamics simulation. The metallurgical attributes of the currently available rail steels are summarised along with an assessment of the life-cycle costs and wider economic implications associated with selection of a rail steel which provides improved resistance to the key degradation mechanisms of rolling contact fatigue and wear. Overall, the proposed methodology, which incorporates engineering, metallurgical and economic assessments, provides guidance on the circumstances in which the introduction of alternative rail steels make sense (or not) from an economic perspective.

Prediction of RCF Damage on Underground Metro Lines

London Underground (LUL) is one of the largest metro networks in the world and carried nearly 1.5 billion passengers in 2015. This increasing passenger demand leads to higher axle loads and shorter headways in the railway operations. However, this has a detrimental impact on the damage generated at the wheel-rail interface. In spite of the advances in rolling stock and track engineering, new developments in material manufacturing methods and rail inspection technology, cracking in rails still remains a major concern for infrastructure managers in terms of safety and maintenance costs. In this study, field data from two metro lines on the LUL network was analysed to identify the distribution and severity of the different damage types. Detailed vehicle dynamics route simulations were conducted for the lines and the calculated wheel-rail forces were investigated to assess the applicability current models for the prediction of rail damage on metro lines. These models include the Whole Life Rail Model (WLRM), previously developed for Great Britain (GB) main line tracks, and Shakedown theory. The influence of key factors such as curve radius, different friction conditions, track irregularities and wheel-rail profiles on the wheel-rail contact interface have been evaluated and compared with outputs from simulations on mainline routes. The study found that the contact patch energy (Tγ) and the interaction between wear and RCF in rails were highly influenced by the characteristics of metro tracks. It was also shown that both the Tγ and Shakedown methods can provide successful prediction of damage susceptibility of rails. However, in order to increase the accuracy of damage predictions and to ascertain the severity of different damage types, the duty conditions which are observed by the rail and the changes in contact conditions resulting from the successive vehicle passes should be considered in the modelling.

Use of NDT Inspection Data to Improve Rail Damage Prediction Models

Infrastructure managers (IMs) endeavour to eliminate rail defects at an early stage since they impact on safety and quality of operation and increase system costs. London Underground (LUL) uses several non-destructive testing (NDT) techniques in rail inspection to detect the emerging defects and monitor the growth of previously recorded defects. This task mainly aims to prioritise maintenance and renewal activities and record their completion. However, when the high traffic demand and limited maintenance periods are considered, these requirements bring additional pressures to the maintenance team. To optimise maintenance planning, sufficient and reliable field data along with accurate damage prediction are required. Recent developments in NDT technology has seen the introduction of devices to measure crack depth which is a key parameter in the assessment of crack severity and rail life. Therefore, contrary to previous research which mainly utilised observations of rail surface condition, the use of new NDT techniques can support the development and validation of new rail damage models which will help to improve maintenance planning and move to condition-based maintenance strategy.