Abstract
Surface defects decrease the fatigue limit of metals. In this study, the effects of surface defects on the fatigue limit of high-strength spring steel specimens were investigated. Several equations to predict the fatigue limit of specimens with surface defects were evaluated. Specimens with a semicircular slit with depths ranging from 30 to 400 µm were prepared. The Vickers hardness of the specimen was approximately 470 HV. Bending fatigue tests were performed at stress ratios ranging from −2 to 0.4. The fatigue test results showed that the fatigue limit decreased with an increase in the slit depth. Moreover, the maximum defect size that resulted in a decrease in the fatigue limit was dependent on the stress ratio. On comparing the predicted fatigue limits with the experimental results, it was confirmed that the predictions made based on the modified El-Haddad model were in good agreement with the experimentally obtained data. Thus, this model can be used to evaluate the fatigue limit of high-strength steels containing small surface defects with different stress ratios.
Highlights
Introduction and Stress RatioMetals 2021, 11, 483.There is an increasingly strong demand for improving the fuel efficiency of automobiles from the viewpoints of energy consumption and environmental pollution [1]
It can be concluded that the defect size that results in a decrease in the fatigue limit of smooth specimens is dependent on the stress ratio
Plane-bending fatigue tests were performed on specimens of spring steel SUP9A (470 HV) at various stress ratios wherein the specimens had semicircular slits with depths of 30 to 400 μm that simulated microsized surface defects
Summary
Introduction and Stress RatioMetals 2021, 11, 483.There is an increasingly strong demand for improving the fuel efficiency of automobiles from the viewpoints of energy consumption and environmental pollution [1]. Reductions in the weight of automobile parts such as springs, gears, and axles are necessary. This in turn requires improving the fatigue limit of the metals used. It is known that the fatigue strength of high-strength steel is reduced sharply by small defects [8,9]. This is because the defect sensitivity of materials generally increases with their strength. If the fatigue limit of high-strength steel with such small defects can be predicted with high accuracy, it is expected that the failure of springs and other parts can be controlled.
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