Abstract
An etching technique was used to study the dislocation microstructure in single crystals of copper fatigued to saturation in push-pull at constant plastic strain amplitude. In agreement with earlier electron microscope studies a structure of plane, regularly spaced walls of dislocations perpendicular to the primary slip direction was found to be associated with the persistent slip bands. The wall spacing (1·38 ± 0·05 yum) was measured and found to be virtually independent of fatiguing frequency (between 0·01 and 25 Hz) at room temperature. The internal consistency of the results was used to justify the etching technique.