Technical Reports

Fatigue Defect Origination and Growth Experiment

  • 01
  • Dec
  • 1991
AUTHOR: Paul Clayton, Glenn Brave
SUBJECT: Facilities & Test Equipment, Rail and Infrastructure Integrity
KEYWORDS: Rail Steel, Shell, Detail Fracture, Facility for Accelerated Service Testing, Shell Index
ABSTRACT: Between 1985-87 a number of different rail steels were tested at the Facility for Accelerated Service Testing (FAST) in the High Tonnage Loop using 100-ton capacity cars. Fatigue data on the formation of shells and detail fractures and growth rates of detail fractures were obtained. The tendency of rail steels to form shells has been related to a parameter termed the Shell Index. This incorporates the volume fraction of oxide non-metallic inclusions, the tendency of those inclusions to form stringers, and rail hardness. The shell rate can be reduced by lowering the oxide content, reducing stringer formation, and increasing hardness. All three factors have to be considered in predicting rail steel behavior. Under the specific test conditions employed, the crack propagation of detail fractures between 10 and 28 percent head area can be modeled by a linear function of million gross ton (MGT). The average growth rate for this size range was between 1.6 and 2 percent head area per MGT. An investigation of the effect of lubrication level and high rail gage corner grinding on rail fatigue behavior proved to be inconclusive probably because of the narrow range of experimental conditions employed.