Theory of Slip-Band Formation

The fine structure of slip bands on the surfaces of plastically deformed crystals, as described by Heidenreich and Shockley and by Brown, is explained in terms of the model of dislocation-loop generation proposed by Frank and Read. The back-stress at an active Frank-Read source, produced by an expanding avalanche of about 300 dislocation loops, is shown to be sufficient to stop dynamic loop generation at the source. Slip, therefore, occurs in avalanches separated in time.

Avalanches from other slip systems crossing a slip plane containing an active source lead to the observed stepped surface markings, with successive avalanches from the given source displaced relative to each other.