High Temperature Tread Braking Simulations Employing Advanced Modelling of Wheel Materials
Paper i proceeding, 2015
In this contribution, the mechanical behaviour of a near pearlitic wheel steel of type ER7 is studied. Isothermal experiments of cyclic loading combined with a hold time are performed at several temperatures, ranging from room temperature up to elevated (below austenitization) temperatures. The experiments show a viscous behaviour at temperatures above 300°C. To capture the cyclic hardening/softening and viscous behaviour of the material, a Chaboche model of viscoplastic type is presented and calibrated against the experimental data. The robustness and uniqueness of the obtained material parameters are then ensured by employing sensitivity and correlation analyses. The main goal of this study is to improve the modelling of wheel materials subjected to thermal loading due to tread braking and also to highlight the importance of viscoplastic material modelling. In this regard, finite element analyses of generic heavy haul wheels, subjected to high power drag braking loads, are carried out and comparisons between analyses with plastic and viscoplastic material models are shown. Results are presented for simulated global wheel behaviour, i.e. axial rim displacements during and after braking, and also residual stresses after braking. A conclusion is that the obtained results for a generic wheel with an S-shaped web, which builds substantial stresses in the wheel rim during braking, is rather sensitive to the choice of material model. Substantial differences are found already at 400°C. Moreover, the results indicate that a generic Low-stress wheel, which builds less stresses in the rim during braking, is less affected by the choice of material model. However, at temperatures higher than about 500°C also the results for this wheel are significantly affected by the choice of material model.