応力制御下における任意のき裂を有する金属の疲労限度の定量的評価 : 第2報,正の平均応力下での鋼の場合

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In this paper, push-pull fatigue tests of notched specimens under R=-1, 0 and 0.5 were carried out on annealed 0.1% carbon steel with the Vickers hardness H_v=105 and quenched-tempered 0.5% carbon steel with H_v=582. The fatigue limit of a long crack, σ_<W2>, was obtained from that of a notched specimen with a sharp and deep notch whose radius is smaller than the branch point ρ_0. Using the present and past σ_<w2>data, the effect of the positive mean stress on the ⊿K_w of the long crack was evaluated by using 3.2H_B (≃σ_B) and<σ_s/(3.2H_B), where ⊿K_w is the stress intensity factor range for the purpose of predicting the fatigue limit of a metal with an arbitrary crack, σ_s is the lower yield stress or 0.2% proof stress, σ_B is the ultimate tensile strength and H_B is the Brinell hardness. Although the σ_<w2>decreased with the mean stress, σ_<w2>was cut off by the threshold stress σ_<we>of the plastic deformation at crack tip. For the quantitative prediction of the fatigue limit of a cracked steel with an arbitrary crack length under a positive mean stress, he σ_<w2>and awe values were approximated with simple formulae.
2004-04-25