低合金鋼,ステンレス鋼,ニッケル合金,アルミニウム合金の疲労き裂伝ぱの下限界特性とき裂閉口挙動

概要

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The near-threshold fatigue crack growth behavior is investigated for carbon steel (S25C), low alloy steel (SM50B), stainless steels (SUS430, SUS304 and SUH310), nickel alloy (Hastelloy X) and aluminium alloys (A2017 and A5083) in laboratory and dry air conditions. At higher load ratios, such as 0.8, where there is no closure, ΔK_<th>-values are proportional to Young's modulus, E. At lower load ratios, such as 0.1, however, ΔK_<th>/E-values are dependent on material and atmosphere, due to crack closure. Oxide-induced closure appears on carbon and low alloy steels in laboratory air, while oxide-thickening within the crack is prevented by passive film on stainless steels, nickel alloy and aluminium alloys. Dry air reduces oxide formation on the fracture surface. Roughness-induced closure is stronger in nickel and aluminium alloys than in steels. Fracture surfaces are more crystallographic in the former alloys. Phase-transformation-induced closure results from martensitic transformation inherent to austenitic stainless steels. This transformation, however, opens the crack near the threshold rather than closes it.
一般社団法人日本機械学会の論文
1986-01-25