Residual Stress in Wheels: Comparison of Neutron Diffraction and Ultrasonic Methods, with Trends in RCF
The critical damage mechanism on many GB passenger train wheels is Rolling Contact Fatigue (RCF) cracking in the rim. Evidence from field observations suggests that RCF damage occurs much more quickly as the wheelsets near the end of their life. Wheel manufacturing processes induce a compressive hoop stress in the wheel rim; variations in residual stress through the life of a wheel may influence the observed RCF damage rates. 
This paper describes experiments to measure residual stresses in new and used wheel rims to identify whether this could be a significant factor, and compares the findings from neutron diffraction and ultrasonic birefringence methods. The scope goes beyond previous applications of neutron diffraction to railway wheels and identifies key considerations for future testing. 
Assuming that the as-manufactured stress distribution was similar for all three wheels tested, it is found that the stresses are redistributed within the wheel rim during its life as material is removed and plastic flow occurs. However, the hoop stress near the running surface remains compressive and may not have a large influence on the RCF damage rates.
Residual Stress Characterization by X-Ray Diffraction and Correlation with Hardness in a Class D Railroad Wheel
This article focused on the microstructure characterization and residual stress measurements of the flange from classes D and C railway wheels (called 7D and 7C steel, respectively) to contribute with the residual stress level on new forged wheels flange area. A correlation with the hardness was conducted. The residual stress was measured in three points of the flange using the x-ray diffraction technique, and the microstructure characterization on SEM microscopy. We found the 7C steel has fine pearlite and ferrite microstructures, and 7D steel has degenerated pearlite and bainite microstructures. In the 7D steel, the compressive residual stress in the flange region was higher than in the 7C steel, which is related to the presence of bainite on the microstructure. There was a correlation between the hardness and residual stress value. The knowledge of the residual compression stress level is important for safety train wheels operation. The traction stress generated by the brake system on the wheel is attenuated by residual compression stress.
A comparison of Mode III threshold under simple shear and RCF conditions
Abstract A novel experimental method, previously developed by the authors, has been applied in order to promote Mode III co-planar crack propagation in a bearing steel. The method consists in out-of-phase multiaxial fatigue tests, adopting a stress history typical of sub-surface RCF, onto specimens containing micro-notches that were previously subjected to Mode I pre-cracking at R  = −2. Three defect sizes, expressed in terms of Murakami’s √area parameter, equal to 630 μm, 315 μm and 220 μm were considered. The experimental data clearly show that the threshold conditions for out-of-phase tests is lower than in simple torsional tests, thus promoting the shear growth. This enhanced damage mechanism, which cannot be described neither in terms of fatigue criteria nor in terms of crack driving force at the crack tip, is characterised by intense plastic deformation and rubbing of the crack lips with an opening of the crack faces. In order to compare the multiaxial and torsional fatigue test results the effect of this type of opening on the friction of the crack faces will be investigated.