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Ultrasonic Evaluation of Stresses in Rims of Railroad Wheels

: Herzer, H.-R.; Schneider, E.

Comite Europeen sur les Essais Non Destructifs -ECNDT-, Paris:
7th European Conference on Nondestructive Testing 1998. Vol. 2
Broendby, Denmark, 1998
ISBN: 87-986898-0-00
European Conference on Nondestructive Testing (ECNDT) <7, 1998, Copenhagen>
Fraunhofer IZFP ()
railway wheel; Stress state; texture; time of flight ultrasound

The stress states in railroad wheels are strongly influenced by the heating and cooling process during and after the brakings using brake shoes. Different ultrasonic set-ups to evaluate the stress states in the rims of monoblock railroad wheels are already in use. Although developed by different institutions, the technique used by the set-ups is the same. By measurements of the times-of flight of an ultrasonic shear wave polarized along the radial and along the circumferential direction, the difference of the principal stresses acting in the circumferential and in the radial directions is calculated. The application of this ultrasonic technique presumes that there is no other reason for the times-of-flight differences of the shear wave polarized along the two directions than the stress state. But in numerous older wheels, which are still in use, the manufacturing process caused a texture in the rim. The texture also influences the times-of-flight of the shear wave polarized along the t wo principal axis. Hence, the stresses evaluated for textured wheels are not reliable. Texture is often going along with a significant direction dependence of the grain dimensions resulting in direction dependent ultrasonic attenuation. The direction dependences of the ultrasonic attenuation and of the shear wave time-of flight have been measured using more than 60 wheels of the older types. It is found that both quantities change significantly if there is a texture in the wheel and small changes are observed for wheels without texture or with a slightly developed texture. A threshold value is defined to separate wheels with a strong texture from those with no or with a slightly developed texture. The stress analysis for wheels with a strongly developed texture is only possible if the texture is homogeneous along the circumference of each wheel. The characterization of the stress state in wheels with a slightly developed texture is possible as first results show.