Wear and Rolling Contact Fatigue (RCF) on wheels and rails are influenced by relative motions between the studied rail and wheel pair, and therefore influenced by train dynamics. Wear and RCF assessments using a train dynamics approach provide more accurate and comprehensive results comparing with conventional assessments that often do not consider train dynamics. In addition, considering material property differences, currently available rail wear maps are not able to accurately describe the wear performance of materials that have significantly different properties. This paper presented a method for rail/wheel wear and RCF assessments using 3D train dynamics models. The use of train models allows the consideration of coupler forces, traction, and brakes during the assessment. Wear assessments were conducted by using an in-house rail wear map model developed from the twin disc wear machine at the Centre for Railway Engineering (CRE). The new rail wear map was developed by using the AS 60 rail material (hardness 340 HB). The results indicated that the methods proposed in this paper could be used for rail/wheel wear and RCF assessments. Traction/braking forces and coupler lateral forces had evident influences on wear and RCF assessment. Different wear maps were also shown to have significant influences on the wear rate results.

A methodology that combines simulations of long-term mechanical degradation including maintenance interventions with an assessment of the associated socio-economic impact is proposed. This development responds to an urgent need within the railway sector to enable the evaluation of maintenance strategies from a LCC perspective. The functionality of the methodology is demonstrated in an investigation of rail grinding strategies for a curve on the Swedish Iron-ore line. The results indicate a reduction in LCC of 50% when using a harder rail material (R400HT) combined with annual rail grinding as compared to a softer rail material (R350LHT) and two grinding campaigns per year.

In this work, the authors present a detailed ’train-track’ interaction model of a long freight train operation topredict long-term rail surface damage. In addition to vehicles and track, intermediate maintenance actions inthe form of cyclic grinding passes have also been modelled according to EN standards to effectively representthe evolving wheel-rail interface. The influence of longitudinal train dynamics in the form of traction, braking,gradients, etc are also accounted in the method to reflect their effect on damage evolution. The two-stepmethodology consists of modules each modelling longitudinal train dynamics and long-term rail surface damagerespectively. The multi-disciplinary integrated numerical framework comprising of train, real operational casesand track attributes has been built based on principles of vehicle dynamics, tribology, and fatigue analysis. Themodel has been demonstrated for a heavy haul freight train operation on a 120 km long track section in thenorth of Sweden for which the results have been presented. Also, additional scenarios that can be expected ina real time operation with varying traction/braking, gradients etc have been considered. In the end, thisintegrated numerical framework comprising of 4 T’s namely train, track, tractive strategies, and trackmaintenance can be tuned into a digital twin to guide infrastructure managers regarding the condition of railassets as a function of tonnage passage. This can in turn facilitate predictive maintenance of track depending ontraffic and operation.

Track damage due to progressively increasing tonnage, especially due to longer and heavier freight trains, is one of the major problems faced in the European rail sector. In this context, to stay competitive, optimal track maintenance practices, track-friendly vehicles and safe operations of long freight trains assume prominence.

This PhD thesis studies long freight train operations and the long-term rail surface damage that they cause, to build a computer simulation-based framework for maintenance planning and assessment of running safety. 

The framework is formulated with four parts: long freight train operations, vehicle dynamics, rail surface damage and track maintenance. This is followed by a literature survey on each of the subtopics and how they are linked to each other.Safe operation of long freight trains in infrastructure bottlenecks such as S-curves is studied using three-dimensional multi-body simulations. Based on this, guidelines to build long freight trains and driving scenarios that can keep longitudinal in-train forces within acceptable limits have been provided. 

Multi-body simulation models of various freight bogies, including a novel design, are built and their dynamic running behaviour studied according to EN standards. The key focus is on track-loading and to this effect, methodologies for simulations-based assessment of `track-friendliness' of various bogie designs are studied. Various approaches to quantify rail surface damage using multi-body simulations in the form of wear and Rolling Contact Fatigue (RCF) are studied. Based on this, measures to ascertain similarities and differences in results from different approaches have been put forward. 

The impact of track maintenance, in the form of periodic rail reprofiling activities in different networks, on the evolution of rail surface damage is studied. It is found that optimal maintenance planning can be tailored depending on the type of traffic on the network.

Finally, various parts of the framework have been brought together to form a `train-track interaction' approach to facilitate optimal maintenance planning.

In this work, the authors present a detailed train-track interaction model of a long freight train operation to predict long-term rail surface damage. In addition to vehicles and track, intermediate maintenance actions in the form of cyclic grinding passes have also been modelled according to European standards to realistically represent the evolving wheel-rail interface. The influence of longitudinal train dynamics in the form of inter-vehicle interactions, traction, braking, gradients, etc is also included in this method to reflect their effect on damage evolution. The authors demonstrate that the novel ‘Train-track interaction’ formulation is more complete and therefore better suited to study long-term rail surface damage as opposed to existing ‘vehicle-track’ formulations since the former brings the system dynamics at play, significantly altering the wheel-rail interaction. A key highlight of this work is that the rail surface damage is expressed in the form of evolving rail profiles over a large tonnage passing and by depicting RCF-affected zones. This framework can be tuned into a digital twin to guide infrastructure managers regarding the condition of rail surface as a function of tonnage passage. This can in turn facilitate predictive maintenance of track depending on traffic and operation.

There are several fatigue-based approaches that estimate the evolution of Rolling Contact Fatigue (RCF) on rails over time, built to be used in tandem with Multi-Body Simulations of vehicle dynamics. However, most of the models are not directly comparable with each other since they are based on different physical models even though they shall predict the same RCF damage at the end. This article studies different approaches to quantifying RCF and puts forward a measure for the degree of agreement between them. The methodological framework studies various steps in the RCF quantification procedure within the context of one another, identifies the ‘primary quantification step’ in each approach and compares results of the fatigue analyses. In addition to this, two quantities - ‘similarity’ and ‘correlation’ have been put forward to give an indication of mutual agreement between models. Four widely used surface-based and subsurface-based fatigue quantification approaches with varying complexities have been studied. Different operational cases corresponding to a metro vehicle operation in Austria have been considered for this study. Results showed that the best possible quantity to compare is the normalized damage increment per loading cycle coming from different approaches. Amongst the methods studied, approaches that included the load distribution step on the contact patch showed higher similarity and correlation in their results. While the different approaches might qualitatively agree on whether contact cases are ‘damaging’ due to RCF, they might not quantitatively correlate with the trends observed for damage increment values. 

Wear and Rolling Contact Fatigue (RCF) on wheels and rails are influenced by relative motions between the studied rail and wheel pair, and therefore influenced by train dynamics as well. Wear and RCF assessments by suing train dynamics provide more accurate and comprehensive results. In addition, considering material property differences, previous rail wear maps may not be able to accurately describe the wear performance of materials that have significantly different properties. This paper presents a method for rail/wheel wear and RCF assessments using 3D train dynamics models. The use of train models allows the consideration of coupler forces, traction, and brakes during the assessment. Wear assessments were conducted by using an in-house rail wear map model developed for a twin disc wear machine at the Centre for Railway Engineering (CRE). The new rail wear map was developed by using the AS 60 rail material. Results show that the older BS11 rail material wear rate regimes and transitions are evidently different to the wear behaviour measured for AS60 rail material.

A methodology that combines simulations of long-term mechanical degradation including maintenance interventions with an assessment of the associated socio-economic impact is proposed. This development responds to an urgent need within the railway sector to enable the evaluation of maintenance strategies from a LCC perspective. The functionality of the methodology is demonstrated in an investigation of rail grinding strategies for a curve on the Swedish Iron-ore line. The results indicate a reduction in LCC of 20% when using a harder rail material (R400HT) combined with annual rail grinding as compared to a softer rail material (R350LHT) and two grinding campaigns per year.

Long freight trains up to 1500 m in length are currently not in regular operation in Europe. One of the important reasons for the same is high inter-wagon forces generated during the operation, especially when pneumatic (P-type) brake systems are used. For long trains with multiple locomotives at different positions along the train, radio communication with necessary fail-safe mechanisms can be used to apply the brakes. Long freight train operation on a given line is subjected to various attributes such as braking/traction scenarios, loading patterns, wagon geometries, brake-block materials, buffer types, track design geometries, etc., which are referred to as heterogeneities. The complex longitudinal train dynamics arising in the train due to various heterogeneities play a major role in determining its running safety. In this context, the maximum in-train force refers to the maximum force developed between any two wagons along the train during operation. The tolerable longitudinal compressive force is the maximum compressive force that can be exerted on a wagon without resulting in its derailment. Here, the authors adopt a bottom-up approach to model pneumatic braking systems and inter-wagon interactions in multibody simulation environments to study the complex longitudinal train dynamics behavior and estimate maximum in-train forces and tolerable longitudinal compressive forces, subjected to various heterogeneities. These two force quantities intend to facilitate a given freight train operation by providing guidelines regarding the critical heterogeneities, that currently limit its safe operation. In doing so, the authors propose the notion to have an operation-based approval for long freight trains using the simulations-based tool.

The wheel-rail interaction constitutes a complex kinematic coupling that evolves over time due to various factors such aswear, rolling contact fatigue and periodic maintenance activities, that determine the rail service life. The state of the rail surface after aspecified traffic and tonnage passing reflects the track-friendliness of the vehicles. This is particularly helpful in guiding track accesspricing strategies for different vehicle designs based on the amount of damage they cause to the track. A complex and highly non-linearmulti-body simulation environment is set up and iterative vehicle dynamics calculations are performed, along with the implementationof recently developed wheel-rail contact models, damage models and maintenance procedures over a 100 MGT tonnage period.