13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- singular pits, but rather comprised of multiple needlelike pits. The observed synergistic effects of environmental, material and loading parameters on the environmental acceleration of fatigue crack growth in low-alloy RPV steels are discussed in [29]. Sivaprasad [30] noted the mechanism of corrosion fatigue crack growth for the two HSLA steels changes with attendant change in the Paris slope, and temperature, water flow speed, ionic concentration, material quality, and load condition play a crucial role in the behavior of fatigue crack propagation of SUS 630 [28]. Bjerkén [31] examined the manners in which the cracks grow and coalesce on the surface and showed that the cracks avoid each other initially and coalesce crack tip to crack side. 3.2 Stress intensity factor/ stress concentration factor around corrosion pits Ramsamooj [32] suggested the parameters needed to predict corrosion fatigue might be the crack velocity caused by stress-corrosion, the applied mechanical stress, frequency, and the threshold stress intensity factor. Cerit and Genel [33] investigated the stress distribution at the semi-elliptical corrosion pits and pointed out that the aspect ratio is the main parameter affecting the stress concentration factor (SCF). The initiation and propagation of the non-propagating crack at the bottom of the artificial corrosion pit, were explained with the stress concentration factor of the pits and the stress intensity factor (SIF) range of the crack tip in [34]. Sankaran et al [4] concluded that the effects of pitting corrosion on fatigue lives can be related to the effects of equivalent stress concentration factors that are routinely used in structural design. Eduardo R. de los Rios [35] proposed an equation to evaluate the stress concentration as a function of distance from the pit center. Carpinteri et al [36-38] calculated the SIF of elliptical-arc surface cracks and the maximum stress-intensity factor is obtained at the deepest point on the crack front. W. Guo [39] showed that the SIF is strongly dependent on SCF, and the influence of notch geometry is negligibly weak for a given stress concentration coefficients. Toribio’s [40] review on SIF for surface cracks in round bars under tension loading indicated that SIF increases with the crack depth and decreases with the crack aspect ratio and changes continuously from the crack center to the crack surface. 3.3 Effect of the corrosion pit on fatigue life The influence of the pitting was on initiation and very early growth stages of fatigue. Further reductions in fatigue lives were associated with increases in pit size. And corrosion fatigue lives were reduced by 40-50% from those of pristine samples [27]. Y. Kondo [10] proposed a residual life prediction method for fatigue crack initiation for the case where crack initiation is controlled by pitting. P. Shi [22] studied on the damage tolerance approach for probabilistic pitting corrosion fatigue life prediction and found that pit nucleation time and the material constant for short crack growth are the two most important random variables affecting corrosion fatigue life. Emilio Bastidas-Arteaga [24] developed a model to predict the corrosion fatigue lifetime. The results showed that the coupled effect of corrosion-fatigue on structures strongly affects its performance, leading to large reduction in the expected lifetime. Together with the rotating bending fatigue tests with various loads on shaft specimens in various extent of pitting corrosion conditions and the fatigue fracture surface analyses, the fatigue lifetime of SUS 630 shaft under various extent of pitting corrosion condition is found to be in a range of
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