高強度鋼の疲労き裂進展特性に及ぼす真空環境の影響

-ΔK 漸減試験による長いき裂の挙動-

抄録

Sub-surface fractures are known as a characteristic fatigue mode of high strength steel in the very high cycle region. To reveal the mechanism of sub-surface fractures, ΔK-decreasing tests were conducted in high vacuum and air environments based on the idea that sub-surface cracks are exposed to a vacuum-like environment. As a result, fatigue crack growth rates in high vacuum were slower than those in air. In high vacuum, fatigue crack growth still took place at a considerably low rate around 10^-13 m/cycle, and the effective threshold stress intensity factor rage (ΔK_eff) in high vacuum lower to that in air. Unlike in air environment, negligible effects of oxide-induced crack closure in vacuum was considered as the reason for the results. The behavior of fatigue crack growth properties in high vacuum well explained the characteristics of sub-surface crack growths in very high cycle regime.