Endurance Limit Enhancement of Notched, 1018 Steel in Sea Water—Specimen Size and Frequency Effects

Notched 1018 steel specimens of three different thicknesses have been fatigued at 31 Hz in sea water as a function of both stress and electrochemical potential. Additionally, specimens of one thickness were fatigued at 3.3 Hz. The phenomenon of endurance limit enhancement, whereby cathodic polarization renders notched steel more resistant to fatigue in sea water than in air, was found to be more pronounced for the lower frequency and for the thinnest specimen. It is projected that endurance limit enhancement is a consequence of calcareous deposits which accumulate within the fatigue crack. The extent to which such deposits occur is thought to depend upon the cathodic current density within the crack and the extent of mixing between the bulk and crack electrolytes, as the latter is ejected and ingested on each cycle. A possible influence from hydrogen is also discussed.