2D FE simulations of elasto-plastic thermomechanical stresses during heating and cooling have been combined with analytical evaluations of resulting stress intensities for thermal cracks. The analyses have identified critical sizes for pre-existing semi-elliptical, radial surface cracks with respect to propagation under thermal loading. Furthermore, resulting crack lengths after propagation have been identified. In addition to the presented examples of braking, which both are extreme cases, also 'milder' braking scenarios have been simulated, but are not presented in this paper. For heavy haul conditions, these results imply that fully functional brake systems on heavy haul trains are not likely to induce thermal crack propagation under normal stop braking since the operational speed is too low. On the other hand, as shown in this study, severe drag braking due to malfunctioning brakes may cause very deep cracking. The analysis also concludes that thermal cracking is a static phenomenon related to the most severe brake cycle. This is in line with previous research findings in Meizoso et al. Subsequent crack propagation from, for example, mechanical loading is outside the scope of the current paper, mainly since such an analysis would require completely different types of simulations. The developed methodology is computationally efficient. To further evaluate the implications of the simplifications made, 3D FE simulations of wheel tread heating and analysis of the resulting stressing of a thermal crack have been performed. The results indicate that the engineering model gives conservative estimation of the stress intensity factor for the case studied. The level of conservatism depends on the employed residual stress linearization. It should be noted that full 3D simulations imply modelling and simulation times that are orders of magnitudes higher than the engineering methodology presented here. It is therefore believed that the presented methodology is a useful tool to establish preliminary (conservative) limits on brake power and allowed surface defects and for preliminary failure investigations. Specific cases can then be studied more in detail using full 3D simulations.
Thermal cracking of a railway wheel tread due to tread braking-critical crack sizes and influence of repeated thermal cycles
2013
9 Seiten, 12 Bilder, 3 Tabellen, 12 Quellen
Article (Journal)
English
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