Plastification and Damage in Wheel‐Rail Rolling Contact – Case Study on a Crossing

A fully three-dimensional, dynamic model for a wheel running over a crossing is developed using an explicit finite element program. The full mass of the wheel and the crossing and elastic-plastic material behaviour are considered. The damage in the contact area is investigated with a very dense mesh taken from the dynamic model using a submodelling technique. With this kind of calculations the stresses and strains produced in the wheel and the crossing during the cross-over process can be determined, as well as the respective reaction forces in the bedding and the axle. Calculations for different crossing-geometries are performed. Finally a damage indicator is introduced to identify the probable location of crack initiation. Turnouts, rail joints and small radius curves are the weak points in railway track structure. Crossings are the central part of the turnout. They consist of two wing rails, the crossing nose and two vee rails. For new wheels the transition process of the wheel from the wing rail to the crossing nose happens quite smoothly. In contrast, a worn wheel experiences a considerable change in the inclination of the rolling planes between the wing rail and the crossing nose. Thus, a severe impacting load on the crossing nose is caused ranging from three to four times of the static load transferred from the wheel to the rail. Higher train speeds, heavier axle loads and greater traffic density all increase damage, raise maintenance costs and affect train safety. Therefore, it is necessary to carry out investigations to eliminate or to lower the dynamic response between wheel and crossing. Since wheel loads are transmitted to the crossing nose through a relatively small contact area, localized loading occurs beyond the monotonic elastic limit. So the main prerequisite for the initiation of low cycle fatigue is fulfilled. Stress analysis is the key to understand and predict wear and fatigue behaviour of contacting or impacting bodies. However, very few published studies on the stresses in crossings exist. In the present paper, a three-dimensional, dynamic, elastic-plastic finite element model of a wheel impacting on a crossing is used to receive the full dynamic response of the wheel-rail system. For studying stress and strain distributions in the contact area during the impact, a quasi-static submodel with a very fine mesh is derived from the dynamic model. It consists of a small part of the crossing nose and is loaded with a moving Hertzian contact pressure distribution. Furthermore, the submodel is used for investigations on the onset of damage through introducing a simple damage indicator.