Estimation of crack growth on rails under the combined influence of thermo-mechanical loading due to the sliding of wheel
Development and growth of surface and subsurface cracks on rail profile is one of the major reasons for deterioration of rails near the halting zones. Rail tracks are subjected to combination of thermal loads during the sliding motion of the wheel while braking and structural load due to the weight of the vehicle. In this paper, an FEA model is been developed to study and analyze the effect of coupled thermo-mechanical load during braking on contact stress and contact area at the rail-wheel interface. Both elastic and elasto-plastic FEA models are used and compared with analytical Hertzian approach to accurately predict rail-wheel contact parameters. A synthetic loading spectrum is proposed to simulate the combination of thermal and thermo-mechanical loading cycles on the rail during braking of vehicle. The loading cycle is used to predict the growth of previously present flaws using Modified Paris Law and Generalized Frost-Dugdale approach. It has been found that elasto-plastic FEA is inclined to predict lesser contact stresses than the elastic FEA or Hertzian model. Furthermore, shape of the contact patch for elasto-plastic FEA is observed to be unsymmetrical in the rolling direction unlike the elliptical contact area in elastic FEA approach. Macro scale initial cracks having length more than 2 mm are also realized to grow faster than their smaller counterparts under the combined effect of thermal and mechanical loads.