The UT inspection of the wheel disk is carried out with a multi-probe arrangement. In order to avoid mode conver-
sion and other disturbances the application of shear waves with polarization more or less in the disk plane is necessary
(Fig. 1). Shear wave probes in a pitch and catch arrangement have shown good potential for crack detection with a
tangential orientation. For the different inspection areas at the wheel disk different probe distances had to be taken into
consideration. Fig. 1 shows the principle of the shear wave probe arrangement. Depending on the sound characteristics
of the UT probes the disk is divided in inspection areas. Two inspection areas are printed in the figure whereas for
real wheel diameter three or more inspection areas must be regarded for the detection of tangential oriented defects
using pitch and catch techniques. Beyond radial oriented defects (Fig. 1) are detectable in pulse echo technique. Fig. 2
shows more details of the wheel geometry together with the probe position on the tread. The complex shape of the disk is
clearly visible as well as the assumed inspection areas of the disk. The ultrasonic set up was refined to regard this particular situation. Thus longitudinal waves ore shear waves with a polarization perpendicular to the plane of
incidence cannot be used due to the interaction with the disk surface (mode conversion). In addition to complex wheel
geometries with different disk thickness through which the ultrasound wave travels, other physical barriers must also be
considered, i.e. access restriction for the probe holder at the train. Fig. 3 illustrates the restricted access problem. To overcome these accessibility problems was a serious challenge during our developing work.