DISLOCATION VELOCITIES AT LOW-TEMPERATURES

Measurements of the instantaneous dislocation velocity are presented. These show an upper bound on the dislocation velocity which is indepen dent of temperature. The experiments also show that more than one disl ocation velocity is measurable during an ordinary tensile test, and as the temperature decreases, only the upper dislocation velocity is obs erved. These results are explicable in terms of dislocations surmounti ng barriers inertially, which is a temperature independent process, wh ere the viscosity is temperature independent.