1990 Volume 76 Issue 3 Pages 446-453
In order to consider why and how the fatigue crack growth in steel is accelerated in seawater, effects of environmental variables on fatigue crack growth rates were investigated. In this study, intermediate (Region II) Fatigue Crack Growth Rates (FCGRs) in a 660 MPa tensile strength steel were measured under various environmental conditions at 25°C, using compact type specimens. Those experiments showed that decrease of corrosion rate by cathodic protection at-0.8 V vs. SCE or deoxygenation was not effective to lower the FCGR in synthetic seawater. Also anodic polarization at-0.6 V vs. SCE did not influence the FCGR. These results suggest that corrosion reactions do not influence the FCGR in seawater.
On the other hand, salts dissolved in seawater did not affect the FCGR and the increase of water contents in ethanol and glycerin accelerated the FCGR. Water must be the substance which accelerates the FCGR. In addition, FCGRs in some oils or other noncorrosive liquids, i.e. liquid paraffin, hydraulic oil, oleic acid and linoleic acid were greater than that in air, although the FCGR in 1, 1, 2-trichloro-1, 2, 2-trifluoroethane was almost equal to that in air. Therefore, it was concluded that hydrogen atoms dissociated from environment substances caused the fatigue crack growth acceleration.
