On the characterisation and detection of rolling contact fatigue (RCF) type cracks in railway vehicle wheels using an alternating current field measurement (ACFM) technique

Juna, Anwar Pervez (2017). On the characterisation and detection of rolling contact fatigue (RCF) type cracks in railway vehicle wheels using an alternating current field measurement (ACFM) technique. University of Birmingham. Ph.D.

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Abstract

The development of the alternating current field measurement (ACFM) technique for high-speed inspection of railway wheels/track is important to ensure the integrity of railway assets. The stress and conditions at the wheel/rail contact patch, severity of rolling contact fatigue (RCF) damage and changes in microstructure and hardness with tread depth for railway wheels are investigated. This study employs experimental measurement of RCF defects in railway wheels to understand ACFM sensor signal - RCF defect relationships. The influence of sensor frequency and speed, sensor angle relative to crack angle, lift-off distance, crack propagation angle and inter-crack spacing distance are investigated. Low rather than high frequency sensors are better suited at sizing cracks in railway wheels and track. The optimum signal is obtained when the sensor is oriented parallel to the crack angle. The signal is reduced at higher speeds. The maximum change in the normalised Bx signal component of the sensor’s magnetic field is greater for closely spaced cracks (<5 mm) and thus overestimates the defect. Inter-crack spacing distances of 15-20 mm yield estimates for crack pocket depths that are oversized by 20-36%. The inner cracks in a cluster with four defects yields higher B\(_x\) values than expected and thus significantly over sizes the defects at 15-20 mm inter-crack spacing distances, whereas, the sensor provides reasonable depth estimates for the outer cracks. Crack propagation angle affects the signal. Scans conducted with the probe oriented at 90\(^o\) to the cluster of cracks consisting of a deep central crack surrounded by shallow cracks results in a distinct central sensor B\(_x\) signal that consists of a peak due to a flux leakage effect, thus, identifying the critical defect.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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