鋼材の低サイクル疲労に関する研究 : 第4報 : 平均応力の影響及び疲労強度減少係数

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In our previous paper, a cummulative damage law for the prediction of fatigue life was proposed and in this report, to study a effect of mean stress and a fatigue strength reduction factor, the cummulative damage law was applied to plane, notched and butt welded specimens under axial loaded condition. σ_a-σ_m and σ-1/σ_0-N diagram were obtained by the cummulative damage law and experimental results, where σ_a, σ_m are stress amplitude and mean stress respectively, σ_<-1>, σ_0 are fatigue strength with stress ratio -1 and 0 respectively, and N is number of cycles. σ_a-σ_m diagram is expressed by two straight line segments σ_<-1>-σ_0 and σ_0-σ_B. Relation between a σ_<-1>/σ_0 and N is expressed the form of σ_<-1>/σ_0 =α・N^B, and constants α, β are as follows. for plane specimen ;α=2, β=-0.0753, 10^0≦N≦2×10^6 for notched and butt welded specimens ; α=2, β=-0.0753, 10^0≦N≦10^4 α=1, β=0, 10^4<N Using the above σ_a-σ_m diagram, σ_<-1>/σ_0-N diagram and one S-N diagram, S-N diagrams with arbitary mean stress or stress ratio can be obtained, and from these S-N diagrams, fatigue strength reduction factor may be estimated.
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