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This report develops a fracture mechanics model for railhead transverse defects, specifically detail fractures from rail shell. The model is applied to calculate the failure strength of 71 rail segments which were rejected by inspection, removed, and tested by the Association of American Railroads in three-point bending. Utilizing the defect measurements for each rail, reasonable agreement is obtained between observed failure loads and failure loads calculated from the stress and fracture mechanics analyses. The fracture mechanics analysis is then extended to obtain preliminary estimates of the fatigue performance of defective rails in service. Specifically, the crack tip stress intensity factor is calculated for transverse defects under various types of in-service loading. The fracture mechanics solutions are utilized to calculate conservatively the remaining lifetime of the rail as a function of defect size and magnitude of wheel load. Using a simplified two-dimensional stress analysis and a three-dimensional fracture mechanics analysis, it is calculated that the shear stress reversal experienced as the wheel passes from one side to the other side of a transverse crack is the dominant stress component causing fatigue crack propagation. Recommendations are made for additional analytical developments and experimental programs required to refine the fatigue life predictions and incorporate them into rail risk assessment and reliability optimization programs.
steels, railroad tracks, crack propagation, fatigue life, stresses, structural analysis
Senior analytical engineer, Failure Analysis Associates, Palo Alto, Calif