Investigation of the mechanism of the corrosion fatigue by analysis of cyclic strain and current response

Corrosion fatigue tests on a commercial iron were carried out in a berate b uffer solution containing 5 mol/m(3) NaCl to clarify the evolution mechanis m of the damage current during cyclic straining. By analyzing the strain an d current response induced by the triangular load waveform, it was found th at the damage current steeply increased just after a threshold strain on th e loading cycle and decayed after the maximum strain on the unloading cycle . In order to investigate the relationship between the deformation at the c rack tip and the current response during decreasing strain, the current dec ay induced by the triangular strain was compared with that induced by the t rapezoidal strain. It was found that the decay rate of the current induced by the triangular load waveform was faster than that induced by the trapezo idal load waveform. Therefore, this current response induced by the trapezo idal load waveform was simulated by assuming that this response was attribu ted to anodic dissolution and repassivation at the fresh surface emerged du ring the loading cycle. The simulated current was in good agreement with th e current response measured in the experiment. Consequently, the damage cur rent induced by the triangular load waveform can be attributed to the anodi c dissolution and repassivation processes at the crack tip, fundamentally. However, it was found that this current is also influenced by the deformati on at the crack tip during a decrease in the strain.