V形環状切欠材の回転曲げ疲労強度に及ぼす析出硬化の影響

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The effect of precipitation hardening on rotary bending fatigue strengh of circumferential Y-notched specimens was investigatd at room tmperature by using two commercial steels, I.e. 18 Ni maraging steel and an austentic heat resisting stel, JIS SUH38. The rotary bending fatigue tsts were carried out on th as solution-treated, peak aged and over-aged specimens. The fatigue limits of the smoothe specimens as well as all of the notched specimens were not influenced b yprecipitation hardening in 18 Ni maraging steel. Non-propagating cracks were found in all the notched specimens having the stress concerntration factor, α, of 6.2 except the over-aged specimens. It was also found that the stress concentration factor at the branching point, α_0, is nearly 4. In SUH38, the fatigue limits of the smoothe specimen and the notched specimen with α of 2.1 were found to increase with precipitation hardening, while the fatigue limits for the other notched pecimens having α latger than 2.1 did not change in spite of precipitation hardening. The value of α_0 was nearly equal to 2 in the as solution-treated specimens and 4 in the other aged specimens. Furthermore, nonpropagating cracks were easier to be formed in SUH38 than in 18 Ni maraging steel and in the as solution-treated specimens than in the aged specimens. Discussions were finally made on the fatigue limits by dividing them into the fatigue limit for crack initiation, σ_<w1> and the fatigue fimit for crack propagation, σ_<w2>. Especially the behavior of nonpropagating cracks was discussed on the basis of roughness-induced crack closure.
社団法人日本材料学会の論文
1989-07-15

V形環状切欠材の回転曲げ疲労強度に及ぼす析出硬化の影響

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