Grain size, stress, and creep in polycrystalline solids

If a stress sigma is applied to a polycrystal of grain size L, the mode of creep deformation depends on the answers to the following questions: (I) Does sigma exceed the Peierls stress sigma(p); (II) Does L exceed the dislocation spacing in a Taylor lattice stabilized by sigma(p); (III) Does Lo exceed the value required for a Frank-Read or Bardeen-Herring source to operate within the grain? (IV) Does L(1/2)sigma exceed the Hall-Fetch value required for slip to propagate across a grain boundary? The (L, sigma) plane is thus partitioned into regions in which different creep modes predominate. (C) 2000 MAIK "Nauka/Interperiodica".