Reducing the Diameter of Freight Vehicle Wheels – The Suitability of Q/D as a Control for Wheel-Rail Contact Stress

High wheel-rail contact stress is related to rail damage mechanisms such as gross plastic flow. Such high contact stresses are often generated by freight vehicles which have comparatively high axleloads. On railways in Great Britain (GB) a limit is placed on the ratio of static wheel load (Q) to wheel diameter (D) as a proxy to control contact stress related damage. However, there is increasing interest in the use of smaller diameter wheels on freight vehicles, in order to prolong wheelset life (smaller scrap diameter) and increase capacity within the GB’s constrained structure gauge. GB Railway Group Standards [1] limit Q/D to 0.13 kN/mm. However it is known that a number of freight wagons already operate above this limit, either due to derogations granted against the standard, or as a result of being introduced prior to the standard’s universal application (‘Grandfather Rights’). At least one vehicle type is known to operate with a Q/D ratio of up to 0.165 kN/mm. This paper presents the results of an investigation into the contact stress state of the GB network. This formed part of a larger study [2] undertaken with a view to allowing a reduction in wheel diameters for freight vehicles. The research was conducted as part of the industry’s R&D programme managed by the Rail Safety and Standards Board (RSSB)

Track loading limits and cross-acceptance of vehicle approvals

The requirements for track loading limits are one of the main barriers to simple cross-acceptance of vehicles where rolling stock that is already operating successfully in one (or more) networks has to be retested before it can be approved for operation on another network. DynoTRAIN Work Package 4 studied this area in order to determine whether the additional requirements were justified, or if the process could be made much cheaper and simpler without increasing the risk of track deterioration for the networks. The review of national requirements identified modified criteria and limit values for track forces in some member states; however, these can be obtained from additional analysis of the normal test results with no new tests required. The influence of design rail inclination has also been found not to be significant, provided a realistic range of wheel–rail contact conditions are included in the tests. For line speeds greater than or equal to 160 km/h, the current standards for track construction across the member states appear to be similar. On lower speed lines in some countries, a ‘weaker’ track condition may require a lower limit on one of the vehicle assessment parameters. Track dynamics modelling has shown that the vehicle assessment parameters used in international standards are suitable for use in cross-acceptance for track forces. The use of multiple regression analysis allows the estimated maximum value for relevant parameters to be evaluated for different target conditions and then compared with the appropriate limit value, or with values for existing, comparable vehicles. Guidance has also been provided on the relevant parameters to consider when developing operating controls for different types of track deterioration

Development and Validation of a Wheel Wear and Rolling Contact Fatigue Damage Model

This paper summaries the development of a damage model to predict the deterioration rates of the wheel tread in terms of wear and rolling contact fatigue (RCF) damage. The model uses a description of a fleet’s route diagram to characterise the duty cycle of the vehicle in terms of curve radius, cant deficiency and traction/braking performance. Using this duty cycle a large number of vehicle dynamics simulations are automatically conducted to calculate wheel-rail contact forces and predict the formation of wear and RCF damage, using a combination of the Archard and frictional energy-based (Tγ) damage models. The damage models have been validated using observation data (wear rates and maximum observed RCF damage) acquired from a range of vehicle fleets in Great Britain (GB). Results from the validation of the model are presented along with a review of the wheel turning and observation data. A piece-wise linear regression is fitted to the wear and RCF parameters predicted from the model to determine the damage rates for each wheelset type on the vehicle. These damage rates are used within the recently developed Wheelset Management Model (WMM) to describe how the attributes of the wheel (i.e. wheel diameter, profile shape and tread damage) deteriorate over time and trigger a maintenance or renewal activity when the condition of the wheel matches a particular limiting value. This work formed part of the rail industry research programme managed by the Rail Safety and Standards Board (RSSB), and funded by the Department for Transport, to increase the rolling stock functionality of the Vehicle Track Interaction Strategic Model (VTISM) tool