Dislocations, creep and plastic flow

This mode of deformation has been known for a long time and the experimental evidence prior to 1958 has been reviewed by Glen (1958). Experiments on single crystals are obviously of great help because there must be many extraneous effects in polycrystal- 

Experiments are generally carried out in one of two ways. Either a constant stress is applied to the crystal and its strain is 

The shape of a typical creep curve, obtained in this case by bending a single crystal rod with the crystal c-axis normal to both 

The features of all these curves are an initial period, shown as 

The value of the exponent tn was found to be about i-6 and the activation energy H about 07 eV. The constants B and B have experimental values 

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