Thermo-mechanical analysis of wheel–brake shoe systems under variable heat partition and friction conditions: a numerical approach

To accurately simulate the thermo-mechanical coupling process during tread braking, this study develops a numerical program that accounts for the dynamic variations in heat partition and friction coefficients. High-friction composite and cast iron brake shoes are examined to systematically compare how their time-dependent thermal and frictional properties influence the evolution of temperature and thermal stress fields on the wheel and brake shoe surfaces. Results show that, as sliding speed decreases and friction increases, the wheel tread's maximum temperature and thermal stress rise by 3.8% and 2.6% with composite brake shoes, and by 13.1% and 12.8% with cast iron shoes. Peak values also occur later compared to constant-coefficient conditions, attributed to higher frictional power density from the rising friction coefficient. Dynamic adjustment of the heat partition coefficient with temperature results in minor changes in wheel temperature and stress for both materials, with maximum deviations of 5.31% for the wheel and 4.61% for the brake shoe, suggesting it can be approximated as constant for engineering applications. Incorporating the temperature-dependent properties of CL60 wheel steel shifts the axial position of stress concentration, due to enhanced heat accumulation and the temperature dependence of elastic modulus and thermal expansion. Therefore, material temperature dependence should be considered in practical modeling. The proposed program offers a refined tool for optimizing and assessing braking system performance.