Theory of electroplasticity based on electromagnetic induction

In the 1960s, it was discovered in the former Soviet Union that short pulses of intense electric currents through metallic wires brought about temporary drops in the flow stress of the metal as it is deformed plastically. This became known as the electroplastic effect, or electroplasticity. After more than 50 years of experimental and theoretical research, no consensus has emerged as to the mechanism of the effect. Following a brief review of the principal experimental results, we show that when a current flows through a metal the ionic cores of atoms of the metal experience a force equal to the Lorentz force on the conduction electrons, which arises from the magnetic field created by the current. This is the origin of the pinch effect in metals. We then present a new theory of electroplasticity based on mechanical stresses created by pulsing the current as a result of electromagnetic induction. Unlike earlier theories, the rate of change of the current is treated explicitly in a dynamic version of the pinch effect. Pulses of normal and shear stresses arise with a magnitude that depends on the rate at which the current changes during a pulse and a small number of other well defined variables. Unlike earlier theories which focused on the maximum of the current during a pulse, this new theory highlights the time dependence of the current pulse as well as its maximum value. Experiments to test the theory are suggested. Four mechanisms proposed earlier for the electroplastic effect are reviewed critically in the appendices. They are dislocation unpinning in a magnetic field, electromigration of dislocations, Joule heating, and the static pinch effect. We show that the physics of the first two mechanisms is unsound and the second two cannot explain most experimental observations.