海水中における軟鋼および硬鋼線材の表面疲労き烈成長挙動に及ぼす温度, くり返し速度, および鋼強度の影響

抄録

The investigation of surface fatigue crack growth behavior in sea water was made for low carbon steel wire SWRM 22K, and also high carbon steel wires SWRH 32 and SWRH 42A in comparison with the previous test results of low carbon steel wire SWRM 10 by measuring crack growth rates and examining fracture surface of specimens, varying the testing frequency from 0.09Hz to 15Hz and the temperature from 288K to 308K. The crack growth rates for the tested steels in air were nearly identical in relatively low ΔK region. A particular frequency was found at which the environmental acceleration factor, (dl/dN)_cf/(dl/dN))_air, at ΔK of 5.5MN·m^-3/2 was maximum. The maximum acceleration factor increased as the temperature decreased from 308K to 288K for each steel, and increased as the tensile strength (σ_B) of tested steels increased in order of SWRM 10, SWRM 22K, SWRH 32, and SWRH 42A. The acceleration factor decreased as the testing frequencies increased above the particular frequencies and decreased as the testing frequencies decreased below it for each steel. When tested at lower frequencies, there appeared a critical frequency, at or below which the rate of crack growth in sea water slowed down and finally stopped for each steel. This critical frequency increased as the temperature increased from 298K to 308K for each steel, and decreased as σ_B of tested steels increased in order of SWRM 10, SWRM 22K, SWRH 32, and SWRH 42A. These observations can be explained reasonably by crack tip blunting caused by dissolution in sea water.