Abstract
Enhanced electrochemical activity induced by fatigue has been monitored on testpieces cyclically stressed in aqueous environments. It was manifest as a current transient varying in synchronism with the cyclic stress and superimposed on the normal steady current. Thin-plate testpieces were stressed in reverse bending at 24Hz under potentiostatic control in prescribed aqueous media. The current transient was extracted and displayed on a digital storage oscilloscope. Some results are given for stainless steel, a carbon steel, and a high-strength aluminium alloy, exposed to aqueous chloride, sulphate, and dichromate media. The form, amplitude, and phase of the current transients observed varied with the material, potential, stress amplitude, and elapsed cycles. The results support the passive film-rupture model for crack initiation in passivating metals and suggest explanations for unfilmed metal.
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