The effect of uni-directional stress on the electrode potential of copper in aerated potassium nitrate solutions was studied. The influence of the variables time, temperature, concentration, magnitude of stress, mechanical condition of the metal, and pH was considered. The potential difference between two size #22 B & S copper wires was continuously recorded on a type G Speedomax automatic recorder. A balance pan was attached to one of the wires to which weights were added and the change in the potential difference between the two wires from the pre-stress potential difference was taken as the strain potential. At least four runs, using fresh pairs of wires for each run, were carried out to illustrate each specific point and to show the results have statistical significance and are reproducible. The following results were obtained: (A) Electronegative strain potentials have been obtained for copper metal in aerated potassium nitrate solution; these changes achieve a maximum at the instant of stressing and then decay with a negative acceleration with time. After an initial period of time, the strain potential decayed logarithmically with time. The magnitude of the electronegative strain potential for a given stress increased exponentially with the reciprocal of the absolute temperature and remained essentially unchanged for concentration changes ranging from 0.005N to 0.500N. (B) Experimental evidence was obtained to support the postulate that strain potentials of copper metal in aerated potassium nitrate solution and their time dependence parallel film rupture; the effect of the change in internal energy due to plastic deformation cannot be ignored. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Specimens of quarter-hard electrolytic copper, twenty feet in length and one-quarter inch in diameter, were statically pre-stressed and subjected to impact loading. Dynamic strain vs time traces, for both loading and unloading waves, were obtained using resistance-type strain gages mounted at various positions along the specimens. Permanent strain increments resulting from each impact were determined. Prestress levels ranged from values well below the yield point of the material to values exceeding the yield point. Impact velocities and impact durations were also varied. The experimental strain wave shape and propagation velocity in bars prestressed well below the yield point were found to compare favorably with the theoretical elastic wave shape and velocity. The unloading waves propagated in bars prestressed above the yield point were found to be similar in shape to the elastic waves observed and to propagate at the elastic velocity without diminution of amplitude. For loading waves propagated in material prestressed above the yield point the incipient portion of plastic strain waves was found to propagate at the elastic velocity. The lower strain increments of the plastic strain waves were found to propagate at higher velocities and the highest strain increments were found to propagate at lower velocities than would be predicted from a strain-rate-independent theory. For the loading waves, a method was developed to approximate the dynamic loading curves (stress-strain relation followed during impact loading). Prom the dynamic loading curves, the peak stress levels of the plastic strain pulses were found to be significantly higher than the stresses at equivalent strains on the static stress-strain curve. The results tended, at least qualitatively, to support a strain-rate-dependent wave propagation theory rather than a strain-rate-independent one. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate