改良9Cr-1Mo鋼環状切欠き材の非比例多軸低サイクル疲労寿命

Abstract

This paper presents the results of a study on the notch effect in low cycle fatigue of Mod.9Cr-1Mo steel under multiaxial loading. Tension-torsion multiaxial low cycle fatigue tests were carried out at room temperature using three types of circumferential notched specimens of the steel and crack initiation, failure and propagation lives were experimentally obtained. Two proportional and three nonproportional strain paths were used in low cycle fatigue tests. The crack initiation and failure lives decreased with elastic stress concentration factor but the crack propagation lives slightly decreased with it in push-pull low cycle fatigue. The superposition of torsion straining on push-pull loading caused a reduction of the three lives but they little decreased with elastic stress concentration factor. The three lives in nonproportional loading became smaller than those in proportional loading but showed smaller reduction with elastic stress concentration factor. Local strains at notch root were estimated by Neuber's rule and maximum principal strain, the equivalent strain of ASME Code Case and the path strain were applied for predicting the low cycle fatigue crack initiation and failure lives. The ASME strain range was most suitable for the prediction of crack initiation life and the three strain range gave almost the same accuracy for the prediction of failure life.