Fatigue tests were carried out on real bearings with various types of artificial defects on their outer‐ring raceways. Finite element analysis (FEM) revealed that the stress intensity factor (SIF) ranges and stress ratios were complex and variable, depending on the gap fittings between the outer rings and housings, as well as on the sizes of the initial defects, both of which influenced the fatigue thresholds of the bearings. In order to establish a comprehensive evaluation of fatigue limits under several combinations of bearing geometries and defect sizes, fatigue crack‐growth thresholds were also measured at different stress ratios by focusing on crack‐closure behaviour. Based on all of the analytical and experimental results, fracture mechanics‐based criteria were proposed for the assessment of fatigue fracture in rolling bearings.
In order to predict the failure of mechanical parts, it is necessary to understand the residual stress and its source, the inherent strain. In this study, the distribution of three-directional residual stress components was measured for a carburized18NiCrMo14-6 cylindrical roller test piece which has 80 mm diameter and 240 mm length using a method combining the contour method and the X-ray diffraction method (the extended contour method). Moreover, the inherent strain distribution was evaluated from measured residual stress by inverse analysis. First, it was shown that the distribution of three-directional residual stress components can be accurately reproduced using the extended contour method by numerical experiments of a carburized cylindrical specimen. Next, it was demonstrated that the distribution of three-directional residual stress components can be measured using general-purpose equipment by actually measuring the same type specimen. Furthermore, the inherent strain distribution was evaluated. Compressive residual stress and corresponding inherent elongation strain were detected in the carburized layer. In contrast, tensile stress and inherent shrinkage strain were determined in the layer just below the case. Finally, the factors that generate each inherent strain have been investigated by thermo-elastic-plastic analysis. Possible explanations are (i)the increase in transformation strain due to the change in carbon content, (ii)the delay in martensite transformation and (iii)the decrease in martensite transformation rate due to the decrease in the cooling rate at the core.
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