Occurrence of fatigue in ocean structures is increasingly recognized as an important technological problem. In a recent investigation1 the present authors disclosed that endurance limit of notched, 0.95 cm (0.375 inch) square 1018 steel specimens fatigued in sea water at 31 Hz could be enhanced to approximately one-hundred percent above the corresponding air endurance limit by cathodic polarization. Figure 1 reproduces the results of these experiments as a plot of nominal, maximum stress per fully reversed cycle versus potential, the latter being maintained constant for the individual tests. Open data points correspond to failed specimens and solid ones to specimens which sustained 107 cycles. The latter did exhibit cracks emanating from the notch root; however, in most instances these ceased propagating after the first 2-3 x 106 cycles. Thus, the curve itself defines how endurance limit varied with potential for these particular experimental conditions; and the region under the curve represents that stress-potential regime where fatigue failure did not occur.
