A fatigue model for thermite rail welds.

摘要

The objective of this project was to examine the fatigue behavior of thermite-welded railroad rail and in particular the occurrence of fatigue defects in the rail head. A rail-head local-stress fatigue model (RAHELS) was developed to predict the type of rail-head defect that forms under a given set of operating conditions and to predict the nucleation life of the defect.;Thermite rail welds usually contain pores and alumina inclusions. The effects of these discontinuities were examined for different discontinuity locations, shapes, and orientations. The effects of residual stresses in the rail-head, seasonal temperature variations, vertical wheel loads, tangential wheel loads, and track-foundation stiffness were also explored.;The RAHELS model predicts that the pores in thermite rail welds are much more damaging than the alumina inclusions. Shape and orientation of the pores in thermite rail welds are predicted to have a strong influence on rail-head fatigue defect formation. The most damaging location for pores is predicted to be the same depth at which rail-head tensile residual stresses are maximum. Axial tensile stresses resulting from cold winter temperatures are predicted to be more damaging than axial compressive stresses resulting from summer temperatures. Two different rail-head fatigue defects are predicted for the two different seasons: vertical split head in the winter and shelling in the summer. Increases in either vertical or tangential wheel loads are predicted to increase fatigue damage with vertical wheel loads having a stronger influence. Track-foundation stiffness is predicted to have a negligible influence on rail-head fatigue defect formation which suggests that the stresses directly associated with wheel-rail contact contribute most to the formation of fatigue defects in the rail head.