The effects of straining frequency and stress ratio on polarization current responded to cyclic strain in a commercial iron

Corrosion fatigue tests of a commercial iron were carried out using a cylindrical specimen with a hole in a borate buffer solution containing 5mol/m³ NaCl at a constant passive potential. Polarization current behavior induced by strain cycles has been investigated in order to elucidate the effects of straining frequency and stress ratio. The amplitude of polarization current synchronized with the strain cycle and the phase shift between the polarization current and the strain were calculated. The polarization current obtained prior to the crack initiation was found to be the charging and discharging current of the electric double layer capacitance. The corrosion damage increased as decreasing the straining frequency in the initial stage of crack propagation. The increased corrosion damage was observed at the reduced stress ratio.