Thermomechanical testing and modelling of railway wheel steel

Abstract

Studies of thermal effects of tread braking on railway wheels show that the wheel temperatures may reach above 600 °C, at which the mechanical properties of the wheel steel are significantly impaired. Computational models that simulate the thermomechanical behaviour of the wheels are commonly based on results from laboratory tests which do not reflect actual in-service scenarios. Anisothermal testing and modelling are omitted due to the difficulties in designing relevant experiments and implementation of the results. In this paper, a preexisting numerical material model is extended in order to implement fully anisothermal behaviour. This is done by performing several thermomechanical experiments mimicking real-world service and worst-case scenarios ranging from room temperature up to 650 °C. The results from the laboratory testing are then used in combination with data from traditional isothermal tests to optimise the numerical material model by calibrating its material parameters. As part of this process it was found necessary to include a time- and temperature-dependent, non-recoverable (irreversible) mechanism for material softening and microstructural changes which occur above 400 °C. Finite element simulations with the material model using the new parameters and the softening law show markedly improved adherence to anisothermal and strain-controlled experimental results compared to the preexisting model(s). The results demonstrate that anisothermal testing is a requirement for models that are intended to simulate material behaviour for thermomechanical loads and thermally induced microstructural changes.