Choice of evolution equation for internal stress in creep

The internal stress values in the course of the primary and the steady-state stages of creep in a Fe3wt.%Si alloy were measured by a technique analogical to the strain transient dip test technique. Two types of evolution equation, i.e. phenomenological and derived from dislocation kinetics, were examined by correlating them with the experimental data. In the application of the second group of equations, characteristics of the real dislocation structure were taken into account. The results of structure investigations are discussed in relation to the concept of internal stress in both homogeneous and heterogeneous dislocation structures, in the latter case using the composite model of the dislocation structure.