Quantitative Evaluation of Fretting Fatigue Cracks by Grazing SH-wave Using a Waveform Shaping Method

摘要

Fretting fatigue cracks occur on the wheel seat of a railway vehicle axle and are the cause of damage to the axle. In wheel axle testing, a grazing SH-wave ultrasonic testing using a waveform shaping method was proposed to evaluate the progress of the cracks by non-disassembly. The effectiveness of the waveform shaping method was evaluated by testing artificial cracks of a specimen cut from the axle of a conventional train. This method greatly suppressed the ringing of echoes and showed higher distance resolution in ultrasonic testing. The waveform shaping method made it possible to detect both the upside tip echo and the downside tip echo from an artificial crack separately. The height of the artificial crack was estimated by the time difference between the tip echoes. Furthermore, not only the height but also the cracking angle of the artificial crack was evaluated simultaneously by shifting the transducer along the axial direction of the axle. We applied the grazing SH-wave ultrasonic testing with the waveform shaping method to an integrity evaluation for the wheel seat of a wheel set. Although by a conventional pulse driving method unnecessary contact echoes overlapped and appeared as large phantom echoes, by the waveform shaping method such phantom echoes were not detected on account of its effect. The height of a fretting fatigue crack occurring on the wheel seat was quantitatively estimated using the time difference of crack tip echoes, and it was demonstrated that the proposed method would be very useful for testing of the axle.