SEMサーボによるHastelloy-Xの高温疲労き裂発生・成長挙動のその場観察(<小特集>先進材料と信頼性解析・評価)

概要

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In-situ observation using a "SEM servo" of fatigue crack initiation and growth behaviors of Hastelloy-X at 973K in vacuum was carried out. The main results obtained were as follows. (1) A strong correlation between fatigue crack growth (FCG) rate da/dN and stress intensity factor range ΔK=K_<max>-K_<min> in the lower rate region from 2×10^<-11> to 4×10^<-8> m/cycle was found, which suggested a relationship in the form of da/dN=C(ΔK)^n, where n was 7. 2. Furthermore, the threshold for FCG, ΔK_<th>, could not be recognized. (2) In-situ observation showed that the fatigue crack propagated within the grains as a transgranular crack and also combined with microcracks in grains. (3) The S-N diagram for an ultralong life of 10^8 cycles was obtained, which showed the relation S=-32 log N_f+348. Also, by in-situ observation, the relation between S and crack initiation life, N_i, was found to be S=-32 log N_i+328. (4) By means of a reliability engineering approach to distributed microcrack growth, it was found that a two-parameter Weibull distribution fitted the experimental data of crack length well, which suggested a mixed mode with two values of shape parameter m_t(=m_g+m_c) : m_g for growth and m_c for combination. Therefore, it could be concluded that the fatigue life was shortened due to the combination of microcracks.
社団法人日本機械学会の論文
1995-09-25