Detection of corrosion fatigue cracking through current responses induced by cyclic stressing

Corrosion fatigue cracking of iron was investigated by analyzing current responses induced by cyclic stressing in a borate buffer solution containing 5 mM NaCl. Crack initiation was detected by evolution of harmonic components in the current responses and decrease in phase shift between strain and current responses. After crack initiation, the current response due to depassivation and repassivation at crack tips merged into the current response due to charging and discharging of an electric double layer. The decay of the damage current during unloading was related to both repassivation at crack tips and decrease in surface areas by crack closure.