<p>Rolling contact fatigue (RCF) is a damage accumulation mechanism observed in components with a curved surface, which are designed for rolling motion. RCF is most recognized in the rail industry and can cause cracking of rails and rail wheels. &nbsp;In rolling contact, the near-surface region of components goes through compressive stress as well as shear stress following the Hertz contact theory. The presence of compressive stress suppresses the formation of persistent slip bands (PSBs); these PSBs are typically where cracks initiate in classical fatigue. Instead, cracks in RCF initiate from surface asperities and subsurface inclusions and eventually lead to surface wear and pitting. NDE of railway systems currently relies on eddy current and linear ultrasound to detect cracks; however, current methods cannot detect damage accumulation prior to crack initiation. Further, since RCF is not currently predictable, railway systems are frequently monitored, causing time inefficiencies. Nonlinear ultrasound (NLU) has been extensively studied to characterize damage accumulation prior to crack initiation in classical fatigue, since it is sensitive to dislocation-based damage. While RCF has different damage mechanisms than classical fatigue, NLU could be a useful NDE method because crack initiation is determined by evolution of dislocation structures. However, NLU has not yet been applied to RCF, likely because of complications arising from making measurements on three-dimensional (3D) curved surfaces. In this work, we implement nonlinear Rayleigh wave measurements along the circumference of a disk to evaluate RCF in pearlitic mild-carbon steel (1060 steel). We first introduce custom fixtures based on finite-element modeling and a technique for repeatable ultrasonic measurements on 3D curved surfaces. Rayleigh wave speed and acoustic nonlinearity parameter, β, were then measured at progressive intervals over 80,000 RCF cycles. The results show measurable changes in β in early fatigue cycles, which correlates to the excessive plastic deformation in surface as shown by SEM images. This work shows that nonlinear Rayleigh waves are a potential NDE method for evaluating RCF-related damage on curved steel surfaces, and motivates future work to determine the dependence of beta on RCF damage accumulation.</p>

Feasibility Study of Nonlinear Rayleigh Wave for Evaluation of Rolling Contact Fatigue

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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