3% 食塩水溶液中の低 ⊿K 領域における S45C と HT80 鋼の疲労き裂伝ぱ曲線

概要

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It is known that da/dN vs ⊿K_<eff> curve is independent on stress ratio and predicts the most conservative fatigue life of structures, where da/dN is crack growth rate and ⊿K_<eff> effective stress intensity range. In corrosive environment, however, determining ⊿K_<eff> is difficult because corrosion product within crack promotes the crack closure. The purpose of this study is to describe an experimental method free from crack closure. Such a method is realized by decreasing ⊿K where maximum load is kept constant and minimum load increases with increasing crack length. The experimental results, obtained for S45C and HT80 steels in 3%NaCl water, showed that crack closure did not occur when the test began at an initial condition of ⊿K≃7 MPa・m^<1/2>, R≃0.6 and dK/da=-2.3 GPa・m^<-1/2> and that da/dN continuously decreased down to the region of ⊿K≃0.8 MPa・m^<1/2> and R=0.96. The minimum value of ⊿K obtained in 3%NaCl water was onethird than the threshold in air at higher stress ratios such as 0.8. The crack growth curves thus obtained were useful for analyzing crack closure under constant amplitude loading with R=0.1 in 3%NaCl water.
社団法人日本鉄鋼協会の論文
1986-01-01