Wheel Rim Axial Residual Stress and a Proposed Mechanism for Vertical Split Rim Formation

Railroad wheels are manufactured with beneficial residual compressive hoop stresses, which are imparted by rim quenching and tempering. Hoop and radial residual stresses for wheels have been studied in detail by various organizations over the years and are relatively well characterized. However axial residual stresses, in the orientation across the rim width from back rim face to front rim face, have not been extensively investigated. This paper describes a failure mode known as a vertical split rim (VSR) and describes efforts to measure the axial residual stresses in, 1) new wheels, 2) service worn wheels and 3) wheels that have failed from VSRs. Initial axial residual stress measurement efforts, using core drilling and x-ray diffraction from the tread surface, are briefly reviewed. Further more extensive work using x-ray diffraction to measure axial residual stress on radial wheel slices is described and data are presented, focusing on differences between the three wheel types. The concept of Axial Stress Amplification (ASA) is outlined, and the relationship of axial residual stress to VSRs is discussed. A proposed mechanism for VSR formation is described. Future work, with a goal of reducing or eliminating VSRs in service, is considered.