Technical Reports

Crack Propagation Life of Detail Fractures in Rails

  • 01
  • Oct
  • 1988
AUTHOR: Federal Railroad Administration
KEYWORDS: Crack Growth; Detail Fracture; Fracture Mechanics; Rail Integrity; Safe Crack; Growth Life
ABSTRACT: The results of a comprehensive study of the crack propagation behavior of detail fractures in railroad rails are presented. The study includes full-scale crack growth experiments in a test track under simulated heavy freight train service, similar field tests and observations on revenue tracks, and static tests to determine the breaking strengths of rails containing detail fractures. A fracture mechanics model of the detail fracture is presented, and the results of laboratory tests to determine the basic crack growth rate properties of rail steel are reviewed. Correlation of most of the experimental results by the model is demonstrated. The model is used to illustrate the sensitivity of safe crack growth life to nine railroad environmental factors. The most influential factors are found to be thermal stress in continuous welded rail, the curve high rail position (relative to tangent track), and residual stress in the rail head. The experimental and analytical results indicate that further investigation is required into the influence on residual stress of: track curvature, rail steel tensile strength, roller-straightening of rails, and increases in axle loads above the maximum currently permitted by U.S. freight railroad interchange rules.