LXXVIII. A theory of work-hardening of metals II: Flow without slip-lines, recovery and creep

Abstract

The author's previous theory of work-hardening is extended to account for fine slip. It is suggested that fine slip and coarse slip both have their origin in Frank-Read sources, but that fine slip occurs when the dislocations move slowly. This occurs when the stress Gb/l required to obtain dislocations from a source is less than the stress required to drive them through the obstacles in the lattice without the help of thermal activation. The initial stages of deformation are normally by fine slip, and the hardening in this region is shown to be much slower than for coarse slip. In creep the deformation is normally by fine slip; a discussion is given on this basis of logarithmic creep, which agrees better with experiment than previous exhaustion theories. A new theory is given of Andrade's β-creep, which relates it closely to steady-state creep. Finally a discussion is given of the formation of vacancies during creep.