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An investigation of the nature of changes in electrode potential produced by uni-directional stress Dudley, Robert Stanley

Abstract

The effect of, unidirectional static stress on the electrode potential of copper was studied. Studies were made with both soft copper and cold drawn copper in solutions of copper sulphate and several other electrolytes. The change in magnitude of the electrode potential was found to depend on several variables, time, temperature, stress per unit area, concentration of solution and the electrolyte in solution. Measurement, which was made in most instances with a Leeds and Northrup potentiometer, was between stressed and unstressed pairs of copper wire. Stress was applied by attaching a scale pan to one of the wires and applying weights to the pan. Two main conclusions can be drawn from the results obtained. (1) Strain potential is the result of two separate effects. The first effect, that of the rupture of a surface film is the dominant effect, but the second effect that of the change in internal energy due to plastic deformation cannot be discarded. (2) Strain potential cannot be ignored as a factor in corrosion problems. It has been shown that a stress of 992 kgm/cm² can cause a potential change in the more anodic or active direction of over 50 mv. If stress is applied to a non-homogeneous metal system some portions of the system will be under plastic strain while others will possibly be under plastic strain. The plastic strain areas, which would usually be situated at grain boundaries, would therefore be more active and highly susceptible to corrosion. Failure of the metal could then be caused by stress concentration or by the gradual corrosion of the grain boundaries of the metal system.

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