Ultrasonic Evaluation of Residual Hoop Stress in Forged and Cast Railroads Wheels—Differences

Paper describes the assessment of hoop residual stresses in the rim of monoblock railroad wheels using ultrasonic methods. Dangerous tensile stress builds up during service as a result of heat loads caused by braking with braking blocks/brake shoes. Results of experiments on two types of monoblock wheels are described: on rolled-forged wheels used in Europe and on cast wheels manufactured and used in North America. Stresses in forged wheels are evaluated with birefringence technique. Investigations carried out in various countries, using different ultrasonic equipment, proved that an ultrasonic technique can provide valuable information concerning stress values in wheels during manufacturing and in service. However, they also showed that due to different microstructures in the rim material and differences in wheel plate design, forged and cast wheels present unique problems for ultrasonic stress evaluation. The aim of this paper is to emphasize these differences and to illustrate how they influence ultrasonic readings. The second ultrasonic technique to evaluate stress is proposed to standard cast wheels – technique based on measurements of time of flight of subsurface (surface-skimming) longitudinal waves propagating in hoop direction on both rim faces. Presented data are based on detailed measurements of acoustic properties of monoblock wheel materials and on earlier experiments performed on forged and cast wheels subjected to inductive heating, braking in a test stand or on track.