Fatigue crack growth in severely shear-deformed pearlite

The contact between railway wheels and rails may appear as an insignificant detail in the railway system, but it is of great importance for the safe and economic operation of railways. The wheel-rail contact plays a central role in carrying and guiding the railway vehicle as well as for transmitting forces in accelerating and braking. The wheel and rail materials in the contact area must withstand large loads. These loads cause permanent (plastic) deformation of the material near the surface that modify its properties. Microscopic cracks form at the surface that subsequently lead to wear (material removal) and the formation of deep cracks. Wear causes a gradual shape change of wheels and rails that needs to be rectified by periodic maintenance. Cracks with a certain depth also need to be removed by maintenance, because they can lead to fracture of wheels and rails and thereby to the derailment of railway vehicles in the worst case. Therefore, it is important to understand the formation of microscopic cracks on the surfaces of wheels and rails with respect to wear and crack formation. This requires addressing both the manufacturing process that determines the basic properties of the materials, and the operating conditions that modify the material properties due to the extreme loading. Changes of the microstructure of the materials and the formation of microscopic cracks will be described and investigated by computer simulation models in the project. The investigations focus on the effects of heat treatment during the manufacturing process and plastic deformation during railway operation on the formation of microscopic cracks in the modified material structure. In addition to the simulations, laboratory experiments will be carried out to obtain data about the plastic deformation behaviour and the crack growth behaviour of the materials. These data will be used to parameterize the simulation models and verify the simulation results. The models that are developed in the project should assist the further development of wheel and rail materials. This is done by systematically assessing the effect of different manufacturing conditions and operating conditions on the formation of microscopic cracks to subsequently minimize wear and crack formation in railway operation.