1129 内部破壊を示すばね鋼の疲労特性に対する平均応力の影響(OS11-7 材料の疲労挙動と損傷評価-疲労損傷・寿命予測-)

Abstract

Fatigue tests were conducted for 1800 MPa-class spring steels at various stress ratios. For comparison, similar fatigue tests were conducted for conventional steels whose tensile strength was lower than 1200 MPa. The spring steels exhibited fish-eye fractures, and the origins of these fractures were oxide, TiN and the matrix itself. In contrast, the conventional steels never exhibited fish-eye fractures. The fatigue strength of these steels decreased monotonously as the stress ratio increased, when the fatigue strength was evaluated in tenns of stress amplitude. With these results, application of conventional methods to evaluate mean stress effects, such as modified-Goodman diagram, a power law of a stress ratio and so on, were discussed in case of fish-eye fracture of high-strength steel. As the result, the difference between the spring and conventional steels was negligible. This means that the conventional methods were applicable to the case of fish-eye fracture of high-strength steel within the scope of this research.