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Safety assessment of railroad wheels by residual stress measurements

Residual stresses in railroad wheels may change from compressive to tensile; this change could lead to wheel failure. The current US regulation calls for the measurement of discoloration indicating heating that may lead to unsafe stress. Quantitative measurement by ultrasonic methods is an attractive alternative, since stress causes small changes in sound velocity. We did an extensive series of measurements on ten cast-steel wheels. Two different ultrasonic instruments gave comparable results. Destructive evaluation of stress in three wheels showed a good correlation with the ultrasonic measurements. This suggests a reliable method and a field-usable instrument for quantitative nondestructive inspection.