疲労き裂伝ぱ特性と皮膜厚さの関係

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The relationship between fatigue crack propagation properties and thickness of films such as oxide film and passive film was analyzed. The data of fatigue crack propagation properties employed were obtained for carbon, low-alloy, high-strength and stainless steels in air at test temperatures between -25 and 550℃ and in 3%NaCl aqueous solution, avoiding crack closure. When the relationship of fatigue crack propagation rate, da/dN, to effective stress intensity factor range, ΔK_<eff>, was expressed by da/dN=C^*{(ΔK_<eff>/E)^m-(ΔK_<eff, th>/E)^m}=C^*(ΔK_<eff>/E)^m-(da/dN)^*…(A) where C^* and m were constants, E was Young's modulus and ΔK_<eff, th> was the threshold, the following three equations were obtained : C^*=1.3×10^5ζ^<0.5>…(B) (da/dN)^*=ζ…(C) ΔK_<eff, th>/E=6.7×10^<-4>η^<0.25>…(D) Here, ζ was the thickness of films formed at the crack tip for each loading cycling, which was estimated from oxidation behavior on the alumina-polished surface in air at elevated temperatures and from corrosion behavior on the bare surface in 3%NaCl aqueous solution. The films were the oxide film in air at elevated temperature and the water-adsorbed and passivated films in 3%NaCl aqueous solution. η was the film thickness measured on the fracture surface at the threshold level. Substituting Eqs. (B) and (C) into Eq. (A), and Eqs. (B) and (D) into Eq. (A), two predictions of fatigue crack propagation were obtained. Both predictions were in good agreement with the experimental data.
一般社団法人日本機械学会の論文
1994-02-25

疲労き裂伝ぱ特性と皮膜厚さの関係

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