Technology Digests / Freight Railcar Wheel Sub-Surface Fatigue Crack Growth Monitoring

TD26-025

Date Posted: October 19, 2026
Authors
  • Ryan Alishio
  • Anish Poudel
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Key Findings

  • Post-processing of historical ACWDS data from FAST train operations showed signs of elevated ultrasonic signal amplitudes indicating the presence of small SSFCs in wheel rims and crack growth with accumulated tonnage. Wheels were observed to safely travel more than 40,000 miles on average with detectable SSFCs meaning that there is a good window of opportunity to identify these conditions in wheel rims before they pose operational risk.
  • The SSFC length in wheels was calculated and tracked throughout the history of a wheel using consecutive ACWDS probe counts in an array. Handheld ultrasonic testing (UT) verifications were in line with the reported crack lengths of ACWDS.
  • Between 2016 and 2022, 105 wheels were flagged by the ACWDS. Handheld UT inspection of the flagged wheels showed 67 wheels had SSFCs and 38 were false positives (internal indications could not be verified using hand UT).

Freight Railcar Wheel Sub-Surface Fatigue Crack Growth Monitoring

Little data exists about the formation and growth of subsurface fatigue cracks (SSFCs) in wheel rims that could be used to determine the window of opportunity between when a crack becomes detectable and when it grows to the point of causing operational risk. This Technology Digest discusses the analysis of the data necessary for MxV Rail’s efforts regarding the exploration of various statistical approaches on the historical ultrasonic waveform (signal) data used to identify early warning signs of SSFCs and monitor the progression of SSFCs in the wheel rim. BACKGROUND Freight car wheels with SSFCs can lead to high-impact wheels and/or, in some cases, cracked or broken rims. Rim failures, including rare failure modes such as shattered rim and vertical split rim (VSR), can pose operational risks. The challenge with understanding SSFCs is that they initiate invisibly below the tread surface and little is known on how these cracks grow…