船体構造の疲労強度基準 : 船体縦強度部材の疲労強度基準

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This paper presented the fatigue strength criterion for longitudinal strength members subjected to both still water bending loads and fluctuating wave bending loads under service conditions. Using the modified Miner rule, exponential distribution for long term distribution of wave bending stress during 20 years (10^8 stress cycles) and ordinary S-N_C (N_C : crack initiation life) curves for notched specimens of mild steel, the following allowable tensile stress SAL for fatigue strength criterion was given. [numerical formula] where, S_a : stress amplitude (wave bending stress at a probability level of Q=10^<-4>) S_m : mean stress (still water bending stress) K_t : Stress concentration factor (K_t-values are not to be regarded as absolute values, but as relative values calibrated from experience for structural members) f : usage factor defined as the cumulative fatigue damage ration summed over a period of 20 years. f_L : σ_B/σ_<BM> (σ_<BM> : tensile strength of mild steel. σ_B : tensile strength of another material) Applying the above formula to longitudinal strength members of several ships reasonable results were obtained.
社団法人日本船舶海洋工学会の論文