Variation of Flaw Echo Height at Wheel Seat of Hollow Railway Axle in Cyclic Rotating Bending

Abstract

For a full-sized wheelset with a hollow axle having machined artificial flaws at the fitting part (wheel seat), the variation of flaw echo heights due to cyclic rotating bending was investigated experimentally. The flaw echo heights were measured at different stages of cyclic loading with bending moment applied to the wheelset. The influence of the direction of bending moment as well as the incident direction of ultrasound on the echo-height variation was examined for each flaw. The flaw echo heights varied significantly during the cyclic loading and by the applied bending moment in spite that the size of each flaw was almost constant. The observed echo-height variations are discussed from the viewpoint of the change of contact condition of the axle-wheel interface by the fretting wear during the cyclic loading. The experimental results indicate that the progress of wear at the axle-wheel interface changes the ultrasound reflectivity and influences the measured echo heights. The wear at the interface can also amplify the effect of axis bending moment on the reflectivity and the echo heights. Some implications of the present finding to the ultrasonic testing of axles are also provided.