静的モード I / 変動モード II 混合荷重下での高強度鋼の遅れ破壊き裂進展開始挙動

概要

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Threshold strength of delayed failure, K_<ISCC>, under cyclic mixed mode I and II loading conditions was investigated for a Ni-Cr-Mo steel (SNCM439), that was quenched and tempered at 673 K. When the mode II static stress intensity factor K_<II> or the range of mode II dynamic stress intensity factor ΔK_<II> was superposed on the static stress intensity factor K_I, the threshold strength K_<ISCC> decreased with an increase in K_<II> or ΔK_<II>. The amount of decrease of K_<ISCC> due to the superposition of ΔK_<II> was larger than that of K_<II>. When the ratio of stress intensity factor K_R was large, the crack propagation direction under superposed K_<II> or ΔK_<II> on K_I at near the K_<ISCC> was normal to the maximum tensile stress. Therefore, when the ratio of stress intensity factor K_R is large, the threshold condition on the delayed failure crack growth initiation can be described by the maximum tensile stress criterion, which is given by σ_<θmax>√<2πr>=constant.
1989-12-15