PSI - Issue 42

V.K. Yadav et al. / Procedia Structural Integrity 42 (2022) 594–601 V.K. Yadav et al., 2022/ Structural Integrity Procedia 00 (2019) 000 – 000

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N be the number of cycles) vs stress intensity factor range (∆ K ) was correlated using well-known Paris equation as (Kumar (2009)): = (∆ ) (2)

Fig. 4. EIS-spectra (a) and potential polarization (b) plot of as-received and weld nugget zone.

Fig. 5. EIS-spectra (a) and potentiodynamic polarization (b) plot after various immersion time.

where, C and m are the material constant and their values can be found by fitting the crack growth data on log-log scale. As, fatigue crack growth is a material parameter within the material and independent on the surface condition. Thus, no significant change was observed in the crack propagation rate, the only difference that was observed in the fatigue threshold regimes at both load ratios. The fatigue crack threshold values were lower at R = 0.1 and slightly higher at R = 0.5, for the pre-corroded specimens than the without corroded ones. This change in the fatigue crack threshold would be due to the formation of oxides near the crack tip which resulted in the crack closure effect and crack arrest at higher stress ratio i.e., R = 0.5, due to the high mean stress. When the crack with sufficiently small ∆ K encountered an oxide layer, the crack growth might be delayed and thus decreasing the crack growth.