In-Motion Railcar Wheel Inspection using Magnetostrictive EMATs

Due to cyclic mechanical loading, railcar wheels are subject to the development of internal fatigue cracks in the rim underneath the tread surface. Off-line inspections are extremely laborious and require extended out-of-service time, and most existing in-line inspection systems that use conventional ultrasonics or electromagnetic acoustic transducer (EMAT) techniques have several drawbacks that limit their full-scale deployment in service. This paper discusses the work performed on the initial research and development of a proof-of-concept novel magnetostrictive EMAT sensor for in-motion railcar wheel inspection. Wheelsets with known internal discontinuities and a 3.7 m long panelized track were used to demonstrate the feasibility of the developed approach and methods. The results obtained from these tests have shown that the magnetostrictive EMAT sensor that generates 5 mm wavelength shear horizontal waves detects both surface defects and internal fatigue cracks with an excellent signal-to-noise ratio. Different wavelengths can also be added to the sensors to enhance or complement the detection of fatigue cracks at different depths. A total of four or five sensors located at standard concrete crosstie spacing along each rail would be able to provide complete coverage on wheels ranging from 711 to 965 mm in diameter with ±90° wheel coverage per sensor, and a theoretical inspection speed of 56 kph can be achieved using this approach.