鋼材の低サイクル疲労に関する研究(第3報) : 切欠き材の低サイクル疲労きれつ発生寿命

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In the previous paper, a cumulative damage law for prediction of fatigue life of unnotched plate was proposed and in this report, using the proposed cumulative damage law, fatigue crack initiation life of notched plates subjected to cyclic loading in low cycle range was discussed. It is assumed that initiation of an engineering size crack at a tip of notch was not only dependent on the local cyclic plastic strain Δε_p and cyclic creep rate Δε_m at the notch root, but on strain ratio |ε_x|/ε_y at the notch root and plastic strain concentration factor K, which represent some mechanical condition near the notch root. As fatigue damage by Δε_p and Δε_m was assumed to be ΣΔε_p^a and ΣΔε_m respectively, so the effect of |ε_x|/ε_y and K are assumed to be represented by a following form. a_N=a_P・F(|ε_x|/ε_y, K_ε) where a_P and a_N are exponent for unnotched plate and for notched one. In the above expression, decrease of |ε_x|/ε_y and K shorten the initiation life. In order to decide an experimental formula of function "F", notched specimens of mild steel were tested under constant repeated axial load and function "F" was found as follows a_N=a_P{0.483 exp(1+|ε_x|/ε_y)-1.01} {-1/K^0.12+2}
社団法人日本船舶海洋工学会の論文