When dislocation processes controlled the creep properties of polycrystalline copper, the experimentally observed effects of grain size variations and of pre-straining at room temperature illustrate the importance of distinguishing between the contributions made by the grain interiors and the grain boundary zones to the overall rates of creep strain accumulation.

Strain Accumulation during Dislocation Creep of Prestrained Copper. B.Wilshire, C.J.Palmer: Materials Science and Engineering A, 2004, 387-389, 716-8