| Summary: | 碩士 === 國立屏東科技大學 === 車輛工程系所 === 105 === In this thesis, the effects of cyclic braking load on the wheel-rail contact residual stress and fatigue life of rail are explored using the three-dimensional thermal elastic-plastic finite element model. The nonlinear kinematic hardening behavior of the rail steel is employed throughout the numerical simulations. The temperature-dependent material properties and friction coefficients are also considered in numerical analyses. Instead of a train braking model, a single wheel and rail contact braking model is proposed to save the computer time. The normal contact pressure, tangential contact pressure and heat flux are obtained from the single wheel and rail braking model. A program is written to apply these parameters to the simplified train model for the train braking analysis. Numerical simulations are performed to explore the effects of the initial braking speed, number of cars, distance between wheelsets and train deceleration on the wheel-rail contact pressure, temperature, and residual stress distributions, respectively. Finally, the fatigue analysis software fe-safe is used to estimate the fatigue life of rail crack initiation.
The numerical results show that the thermal contact stresses and temperature distributions are influenced significantly by the braking speed and wheel-rail contact passes. The residual stress and residual strain of the rail increase with increasing number of wheel passes. In addition, the results of fatigue analysis indicate that a higher initial braking speed results in a shorter fatigue life of the rail. Based on the theory of strain-based life, the predicted fatigue lives of rail are 203, 105 and 42 when the initial braking speeds are 180, 240 and 300 km/hr, respectively. The literature points out the use of two-dimensional models, based on the theory of strain-based life, the predicted fatigue lives of rail is 3 when the initial braking speeds is 300 km/hr. Therefore, the use of two-dimensional model for fatigue life prediction is more conservative.
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