Localized Plasticity Pattern at the Prefracture Stage: Origin and Development

A pattern of macroscopic deformation bands with a characteristic size of ~10 mm was revealed experimentally in a uniaxially deformed sample at the prefracture stage prior to macroscopic necking. The bands moved at different velocities to the place of subsequent necking. The observed banding pattern in the deformed medium was described using two identified dynamic order parameters, which are the amplitudes of unstable plastic and elastic deformation modes. The change in the dynamic order parameters was described by a system of two coupled nonlinear parabolic equations. Analysis of solutions to the equations revealed the conditions for the formation and development of the found pattern at the prefracture stage.