2320 フレッティング疲労の諸特徴と力学的根拠(J09-1 フレッティング,機械的締結,J09 締結・接合部の力学・プロセスと信頼性評価)

Abstract

Fretting fatigue process have many features such as early stage crack initiation at contact edge, very slow crack propagation and fatigue failure after very long life operation. In previous paper we present new fretting fatigue model which can explain these fretting fatigue features reasonably. In this paper we try to explain other many fretting features such as fretting fatigue strength and life dependence on contact pressure, contact edge shapes. Firstly we try to discuss the dependence of fretting fatigue strength/life on contact pressure. In accordance with the increase of the contact pressure the stress concentration at contact edge increase and crack initiation stress level decreased. But to open this small cracks initiated at contact edges more wear or more load cycles are needed. So fretting fatigue strength limit decrease in accordance with the increase of contact pressure and fretting fatigue life increase in accordance with the increase of contact pressure. Then we discuss the fretting fatigue strength dependence on contact edge shape, such as stress release projection or interference of contact edge with stress concentration fillet. And experimental results of fretting fatigue strength improvement with stress release projection can be explained analytically. The two-stage S-N curve can be shown in joint structures, in which contact edge is set near the stress concentration fillet. These feature also can be explained analytically in this paper.