高強度鋼の遅れ破壊き裂進展開始挙動に及ぼすモードII変動応力重畳の影響

概要

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The crack growth initiation behavior in delayed failure under superposed static or dynamic mode II stress on mode I static stress was investigated on the precracked specimens of Ni-Cr-Mo steel that was quenched and tempered at 673 K. When the superposed mode II static stress intensity factor K_<II> or the range of mode II dynamic stress intensity factor ΔK_<II> on the static stress intensity factor K was relatively small, the crack initiation time t was longer than that when K_<II> or ΔK_<II> was zero. When K_<II> or ΔK_<II> was large, however, t_i decreased with an increase in K_<II> or ΔK_<II>. The crack propagation direction under superposed K_<II> or ΔK_<II> on K_I is dependent on fracture mechanisms. When hydrogen embrittlement governed the mechanism, the crack propagation angle θ_p once increased with an increase in ΔK_<II>/K_I and decreased with a further increase in ΔK_<II>/K_I. In the case of fatigue θ_p small when ΔK_<II>/K_I was small and increased with an increase in ΔK_<II>/K_I. The crack propagation under superposed AK_<II> on K_I in water occurred by the hydrogen embrittlement type when ΔK_<II>/K_I was small, and changed to the fatigue type when ΔK_<II>/ K_I became large.
1988-07-15