Management And Understanding Of Rolling Contact Fatigue

Phase 1 Mechanisms of Crack Initiation

The severe stresses at the wheel-rail contact cause wear of both wheel and rail. Although this is a fairly slow process, even slight changes to the geometry of the wheel and rail can cause major changes in the running behaviour of trains.The group has created a unique computer simulation to model rail wear, and its development and improvement is ongoing. Currently, rail material is represented as a mesh of rectangular elements, and to mimic microstructure the material properties vary from element to element. Applied stress varies with depth and the elements accumulate damage and fail at different rates. To simulate wear elements can be removed as the material fails. Failure is based on the extent of plastic deformation of the steel. The wear model will be developed to consider surface roughness, additional failure mechanisms, and to move to 3 dimensions from the current 2d software. In addition, the integration of crack initiation models with the wear simulation is an area which is being developed.Phase 2 Crack GrowthHow cracks grow, and how fast, is being investigated using computer modelling and experimental testing.Rail-wheel contact forces drive much of the damage, but other issues such as welds, residual stress following rail manufacture, and maintenance techniques can also affect the rail life. Modelling requires validation and real-life testing. The group is conducting full-scale tests of cracked rails at NewRail’s Barrow Hill test site.