Evaluating Rolling Contact Fatigue Damage Precursors with Rayleigh Waves in 1060 Steel

The operational life of components subjected to rolling contacts such as bearings and rail wheels is limited by rolling contact fatigue (RCF). In RCF, materials undergo complex stresses and plastically deform at surface asperities or subsurface inclusions. The accumulation of plastic deformation in surface layers and subsurface inclusions eventually cause spalling and pitting, which can lead to failure of components. Nondestructive evaluation (NDE) of RCF is currently limited to cracking, however there is currently no NDE method to identify damage accumulation prior to crack initiation. Nonlinear ultrasound (NLU) has been shown to be sensitive to dislocation-based damage and thus early damage accumulation induced by fatigue. While NLU has been studied on two-dimensional curved surfaces, three-dimensional curved surfaces, typical for RCF, has not yet been studied. In this work, we apply nonlinear Rayleigh wave to evaluate RCF on a 1060 steel disc with three-dimensional curvature while the disc is mounted on the RCF setup. Custom fixtures were designed and validated with finite element modeling to repeatably generate and detect Rayleigh waves along the circumference of a disc. We measured the Rayleigh wave speed and the acoustic nonlinearity parameter, β, at progressive intervals over 80,000 total RCF cycles. The results show measurable changes in β with increasing cycles, which correlate to damage accumulation during RCF as shown by scanning electron microscopy. This work demonstrates that nonlinear Rayleigh waves are a promising NDE tool for identification of RCF-related damage on curved steel surfaces that resemble real-world rail geometries. This motivates future work to determine the exact dependence of β on RCF damage accumulation.