鋼材の低サイクル衝撃疲労強度におよぼす平均応力の影響について

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In this study, as a basic study on the impact fatigue of ship structural members under random load induced by sea waves, effects of mean stress on impact fatigue strength of mild steel are investigated experimentally. Low-cycle impact fatigue tests on four kinds of round bar specimens having stress concentration factor K_t=1∼4.7 under alternating axial load of systematically varying stress ratio are carried out. Ordinary fatigue tests are also carried out on the same specimens to make comparison with the above results. The results are summarized as follows: (1) The process of fracture for smooth specimens is a creep type and that for notched specimens having large K_t-values is a crack type independent of the stress ratio R defined by the ratio minimum stress σ^^-_<ca> to maximum stress σ^^-_<ta>. That for specimens having small K_t-values is different depending on magnitude of stress and stress ratio. (2) In the case of the creep type, the relation between permanent strain rate Δε_c and impact fatigue life N_f does not depend on R but the relation between stress amplitude σ^^-_a (=σ^^-_<ta> (1-R)/2) and N_f depends largely on R. In other cases, the relations between σ^^-_a and crack initiation life N_c and fracture life N_f depend largely on R, too. (3) From the above results, it is found that the relation between stress amplitude σ^^-_a and mean stress σ_m for each specimen except the notched specimen having very large K_t-value is given in the following form: [numerical formula] where σ^^-_<-0.8> : stress amplitude for stress ratio R=-0.8 σ'_B : ultimate stress for each specimen. (4) The fatigue behaviour for ordinary fatigue tests is almost similar to that for impact fatigue tests but the degree of effects of stress ratio on the fatigue behaviour is less than that for impact fatigue tests.
社団法人日本船舶海洋工学会の論文
1984-06-30

鋼材の低サイクル衝撃疲労強度におよぼす平均応力の影響について

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