Numerical investigation of thermo-mechanical behavior of railway wheel treads under contact variation and brake-force failure during long-slope braking

This study investigates the thermal response of railway wheels under complex operating conditions, such as long downhill gradients, focusing on potential brake system failure modes. Specifically, it quantitatively analyzes how abnormal variations in brake cylinder pressure and wheel–brake shoe misalignment during steady braking amplify normal contact force, reduce contact patch area, and cause axial shifts in the contact location—ultimately affecting wheel tread temperature rise and thermal stress distribution. Based on theories of dynamics, heat transfer, and tribology, a novel modeling approach is proposed by parameterizing “contact patch area–position” into a tabular heat source. A 1/6 circumferentially symmetric indirect thermal–structural coupled finite element model of the wheel–brake system is established in ANSYS APDL. The model incorporates temperature-dependent material properties and considers convective effects during braking. Its accuracy and convergence are validated against experimental data from the literature. Key findings include: (i) When the normal force triples, the maximum tread temperature and thermal stress increase linearly, with gradients of approximately 11.7 ℃ and 17 MPa per 0.25× increment, respectively; (ii) The tread temperature displays an approximately quadratic increase with the reciprocal of the contact-area ratio, whereas the thermal stress grows in a near-exponential manner. A 25% reduction in contact area results in an average increase of 18 ℃ in temperature and 34.5 MPa in thermal stress, showing an accelerating nonlinear trend; (iii) Field-side axial shifts in the contact patch add 6.8% to temperature rise, with minimal stress impact; (iv) Under extreme coupled conditions, the wheel tread undergoes a 4.9-fold increase in peak temperature and a 7.5-fold increase in thermal stress compared to normal braking. At this stage, the material enters the elastic–plastic regime and becomes vulnerable to irreversible deformation and the development of tensile residual stress zones. This work is to couple the abnormal braking force, contact-patch area, and contact-patch position within a unified numerical framework, thereby elucidating the superposition of thermal-mechanical responses on the tread. This study offers theoretical foundations and data support for the thermal safety design and fault risk assessment of railway vehicles operating on long downhill gradients and in extreme environments such as severe cold and high altitudes.