Equilibrium State of Slip Bands in Plastically Bent NaCl Crystals

Abstract

AbstractThe slip bands known from ionic crystals and being typical for the initial stage of plastic deformation are found to have a limited, narrow width and a defined long‐range stress field in the present case of NaCl crystals tested in bending. This deformation structure has been investigated by combining special methods of photoelasticity, interferometry, and electron microscopy. The stress field of the slip band is described by a pile‐up of edge dislocations which are necessarily in excess within a bent crystal. The superposition of the slip‐band stress field to the applied stress leads to a stress equilibrium which can be reached “statically” or “dynamically” and which explains the limitation of the width and of the integral step height of the slip band. As a consequence of this limitation, the number of slip bands increases considerably during further bending. Thereby the atomic slip steps will cover the surface more and more homogeneously so that after a surface strain of about 1% individual slip bands can no longer be distinguished.