Validation of finite difference methods for brake thermal analysis in wagons with LL-type blocks

The safety of freight trains depends on the performance of braking systems, particularly on the condition of frictional components such as brake blocks and wheels in tread brakes. These components are subjected to thermal and mechanical stresses that cause wear and damage. The aim of this work is to predict the temperature field developing in the wheel–brake block contact region during braking, in order to provide a reliable numerical tool for railway safety and durability assessment. Although finite element models are widely used in the literature, this study proposes two Finite Difference models featuring first-order accuracy in time and second-order accuracy in space: a 2D axisymmetric model and a 3D model to predict the thermal behaviour of wheels and blocks. Vernersson’s analytical relation is applied in the 2D model for the determination of the circumferential temperature on the wheel tread, and the result is compared with that of the 3D model. The accuracy of the models is validated using experimental data from organic LL blocks for tread brakes provided by Trenitalia (FSI group), with an average difference of around 25°C in the worst case. The results temporal evolution shows good agreement between numerical and experimental temperatures and demonstrates that the proposed 2D approach, combined with the analytical circumferential formulation, allows an accurate characterization of the wheel thermal field with a computational time reduction of more than two orders of magnitude compared to the 3D model. Finally, the model is applied to compare the thermal features of organic LL and cast iron brake blocks simulating a bench and an entire train. The analysis highlights that the use of organic LL blocks leads to an increase in wheel circumferential temperature variation compared to cast iron blocks, resulting in a higher thermal fatigue load on the wheel tread.