Tiefenbestimmung von Laufflächenfehlern an Eisenbahnrädern unter Nutzung linearer polarisierter Transversalwellen. Verfahrens-Optimierung und Erprobung
Detection and sizing of cracklike defects in the tread of railway wheels by linearly polarized ultrasonic shear waves. Technique and equipment
Modern rail traffic is characterized by continuous increase of speed and operation hours of the vehicles. Rails and especially the wheels underlie high load which can result in surface breaking cracks in the tread of the wheel. By routine nondestructive inspection checks the forming of cracks is controlled. Once a crack in the tread has been detected its depth is of most interest first due to safety considerations and second due to economical aspects. Detection and Sizing are done by an ultrasonic technique under insonification of linearly polarized shear waves in normal direction into the tyre transmitted and received by a couplant free Electromagnetic Acoustic Transducer (EMAT). The direction of the poloarization is parallel to the direction of circumference. Amplitude and phase of the echoes of the opposite face of the tyre (backwall echoes) are evaluated. If there is a cracklike defect within the sound field of the transducer amplitude and phase of the echo are changed due to a mod e conversion of the incident linearaly polarized shear wave into a rayleigh wave propagating along the flanks of the crack. By scanning the transducer in radial direction of the wheel and recording amplitude and phase of the backwall echo the depth of the crack is determined.