Thermal Capacity of Railway Wheels - Temperatures, residual stresses and fatigue damage with special focus on metro applications

Tread (block) braking is still one of the most common braking systems on railway vehicles.The action is carried out by pressing brake blocks against the tread of a wheel, which is also inrolling contact with the rail. The extensive use of tread brakes in metro and suburbanapplications has created a need for design guidelines or standards for wheels exposed torepeated stop braking. The thermal capacity of the wheels puts a limit to railway tread brakingsystems. With the exception of the drag braking cases described in the European standardEN 13979-1, there are no known standards or guidelines regarding the thermal capacity limitsfor wheels.In the present work, important aspects of the thermal capacity of tread braked railway wheelshave been assessed in a literature survey. Then two different railway wheel designs, withtypical characteristics of freight and metro wheels, have been numerically studied with respectto standard design criteria for load cases of drag braking and stop braking. The influence ofbrake block materials, thermal parameters and brake pressure distribution on the wheeltemperatures has been investigated. A general result is that hot spots only have a minorinfluence on the global heat partitioning in the wheel-block-rail system even though the hotspots have a major impact on local temperatures.Brake rig experiments and a field test campaign were performed and aimed at measuring wheeland brake block temperatures during different service conditions for a metro line. Simulationand calibration tools were employed in order to facilitate a comparison between measuredtemperatures. The results showed the importance of knowing the convection coolingparameters for different wagons if prolonged braking action is to be considered. In a pin-on-discexperimental study of railway braking materials, the heat partitioning characteristics betweenwheel and block material at controlled elevated disc temperatures were investigated by a finiteelement approach where a model was calibrated using measured temperatures.In the final part of the present thesis, a modelling framework was proposed and developed thatrepresents typical conditions in metro and suburban operations, in particular during sequentialstop braking. A parametric study was done for analysing the influence of various loading levelsand other important factors on temperatures, axial flange deflection, residual stresses and thefatigue life of the wheels. The model and the numerical results will be useful for assessing thethermal capacity of wheels and for developing new design rules and standards. It was foundthat the mechanical and thermal loadings have different influences on the web damage and onthe estimated fatigue life depending on load cases and wheel design.