Incubation Periods and the Friction Stress in Dislocation Creep

If the stress is suddenly reduced during a creep test, a period of zero creep occurs before it recommences at a new rate. The length of this period depends on the extent of the stress reduction and consecutive stress drops immediately following a prior incubation period lead to ever-increasing periods before creep recommences. These observations have previously been interpreted in terms of a friction stress for creep, such that the value of the stress remaining when the incubation period apparently becomes infinite is taken to be the friction stress. In this paper an alternative interpretation is given in terms of the time taken for the three-dimensional dislocation network to readjust in size when the stress is reduced. The predictions of the model are compared with, experimental results and limitations of the model are discussed.