Ein neues Verfahren zur Bestimmung von Rißtiefen mit Ultraschall

The method has been used to estimate the maximum depth in railway wheel treads. It is based on a pulse-echo-technique utilizing linearly polarized shear waves incident normally to the rear surface of the wheel rim. When the polarization direction is selected in such a way that the wave is horizontally polarized with respect to the wheel tread surface the shear wave propagates - depending on the probe position along the wheel radius - equally grazing along the surface or into the volume of the wheel rim below the surface. When a crack-like defect is situated within the ultrasonic beam the attenuation of the backwall echo sequence increases significantly even when the defect is oriente oblique or parallel to the propagation direction of the wave. The amount of additional attenuation depends on the probe position with respect to the wheel tread surface. Quantitative evaluation of this effect allows to estimate the maximum defects depth. The method has been studied on artificial notches an d natural cracks (maximum depth between 5 and 18 mm) in railway wheels.