Technical Reports

The Cause of Thermal Fatigue Cracking In Metroliner Wheels

  • 01
  • Mar
  • 1977
AUTHOR: Federal Railroad Administration
KEYWORDS: Metroliner Wheels; Residual Thermal Stresses; Thermal Cracking; Macrostructure; Microstructure
ABSTRACT: One new wheel and two used wheels (one with a thermal crack in the tread) were examined for mechanical properties, macrostructure, microstructure, and residual stresses. Similar examinations were conducted on three new wheels which were first subjected to various braking cycles designed to define the conditions that produce cracking. The braking tests were conducted on the laboratory dynamometer. The results of this study indicated that the wheel that had developed a thermal crack in service had been intermittently and severely heated around the tread surface and that such heating had altered the microstructure, produced residual tensile stresses and permitted the crack to initiate. The results further showed that neither altered microstructures nor cracking could be produced by many emergency brakings or speedreduction brakings with normal brake shoes and forces.