Heavy haul railway operations permit the transport of huge volumes at lower cost than other modes of transport. The low cost can only be sustained if the maintenance costs associated with such railway operations are minimised. The maintenance costs are mainly driven by wheel and rail damage in the form of wear and rolling contact fatigue (RCF). Low wear rates in the wheel-rail interface have resulted in an increase in the prevalence of rail RCF, thereby increasing rail maintenance costs. The aim of this study is to develop an approach to reduce rail RCF on South Africa’s iron ore export line by managing the worn wheel shape. This approach is developed by evaluating wheel and rail profile shapes that contribute the most to RCF initiation, studying the influence of suspension stiffness and rail profile changes as well as a redesign of the wheel profile. The influence of wheel and rail profile shape features on the initiation of rolling contact fatigue (RCF) cracks was evaluated based on the results of multibody vehicle dynamics simulations. The damage index and surface fatigue index were used as two damage parameters to assess the influence of the different features. The damage parameters showed good agreement to one another and to in-field observations. The wheel and rail profile shape features showed a correlation to the predicted RCF damage. The RCF damage proved to be most sensitive to the position of hollow wear and thus bogie tracking. RCF initiation and crack growth can be reduced by eliminating unwanted shape features through maintenance and design and by improving bogie tracking. Two potential mitigation measures had been adapted from those published in literature to reduce RCF. The mitigation measures involved changes in suspension stiffness to spread wheel wear across the tread and the use of gauge corner relief rail profiles. These mitigation measures were evaluated by means of multibody dynamics and wear maintenance costs. These mitigation measures, however, did not prove to be successful in reducing RCF initiation while maintaining a low wheel wear rate. The current operating conditions on South Africa’s iron ore line, although still not optimal overall, were found to be better in terms of their wear and RCF performance than the two proposed RCF mitigation measures. Based on the finding of the study on two RCF mitigation measures it was recommended that a conformal wheel profile be developed to spread the wheel wear across the tread to reduce the occurrence and propagation of RCF cracks, while still maintaining low wheel wear rates. A comparative study of this new wheel profile design and the current wheel profile design was therefore performed using multibody dynamics simulation together with numerical wheel wear and RCF predictions. The advantages of the conformal wheel profile design were illustrated by evaluating the worn shape and resulting kinematic behaviour of the conformal design. The conformal design had a steadier equivalent conicity progression and a smaller conicity range compared with the current wheel profile design over the wheel’s wear life. The combination of a conformal wheel profile design with 2 mm hollow wear and inadequate adherence to grinding tolerances often result in two-point contact, thereby increasing the probability of RCF initiation. The conformal wheel profile design was shown to have many wear and RCF benefits compared with the current wheel profile design. However, implementation of such a conformal wheel profile must be accompanied by improved rail grinding practices to ensure rail profile compliance. Based on these findings an approach is proposed where the conformal wheel profile design together with improved compliance of the in-service rail profiles to the target rail profile are implemented. This has the potential to reduce RCF initiation on South Africa’s iron ore export line. / Thesis (PhD)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

Before vehicles can be placed in service it has to complete an authorisation process. At the moment,this process is largely depended on tests. This is, however, an expensive and long process. With new technologies and improved simulations this process can be shortened and the costs can be lowered. The validation of a vehicle model, however, is often limited by the available data. Often the measured rail profiles are not available and thus a new UIC60 profile is used for the simulations. The railway track often has been used and showssigns of wear and damages, therefore research has been done to investigate the influence of the rail profiles on the validation of a railway vehicle model. The current methods of validation in the European norm are used to compare simulated values with forces and accelerations available from vehicle measurements. In the first step,25 track sections with different curve radii have beensimulated with a measured rail profile every 100 meters. In the next step, the same sections have been simulated by using the standard UIC60 rail profile. The results show that the use of measured rail profiles does have a positive influence on the outcome of simulation. In the final step, one single narrow curve has been simulated to show the effect of standard and worn rail profiles. Four different wear stages of the rail profile are simulated and compared to the available vehicle measurements available. These simulations show that the use of a medium worn rail profile gives the most accurate value. / Innan ett fordon kan tas i bruk måste det genomgå en tillståndsprocess. För närvarande är denna process till stor del beroende av provningar. Detta är dock en dyr och lång process. Med hjälp av ny teknik och förbättrade simuleringar kan denna process förkortas och kostnaderna sänkas. Valideringen av en fordonsmodell begränsas dock ofta av de tillgängliga uppgifterna. Ofta finns inte de uppmätta rälsprofilerna tillgängliga och därför används en ny UIC60-profil för simuleringarna. Järnvägsspåret har ofta använts och visarDärför har forskning gjorts för att undersöka hur rälsprofilerna påverkar valideringen av en modell av ett järnvägsfordon. De nuvarande valideringsmetoderna i den europeiska normen används för att jämföra simulerade värden med de krafter och accelerationer som finns tillgängliga från fordonsmätningar. I det första steget har 25 spårsektioner med olika kurvradier använts.simulerats med en uppmätt rälsprofil var 100:e meter. I nästa steg har samma sektioner simulerats med hjälp av standardprofilen UIC60. Resultaten visar att användningen av uppmätta rälsprofiler har en positiv inverkan på simuleringsresultatet. I det sista steget har en enda smal kurva simulerats för att visa effekten av standard- och slitna rälsprofiler. Fyra olika slitningsstadier av rälsprofilen simuleras och jämförs med tillgängliga fordonsmätningar. Simuleringarna visar att användningen av en mediumsliten rälsprofil ger det mest exakta värdet.