Power law for creep

A model is discussed which gives rise to the widely used power law for creep under constant load, namely, d l /d t = Ω t - n , where l is the strain, t the time, Ω a function dependent on temperature and load and n an exponent which may have any value between 0 and 1. In this model, the exponent n is interpreted as a function of the number of "flow units" which must be activated simultaneously before flow can take place.