AN ESTIMATE OF INTERNAL-STRESS EVOLUTION IN THE PRIMARY CREEP BASED ON THE COMPOSITE MODEL OF DISLOCATION-STRUCTURE

The paper gives an estimate of the average internal stress which can b e measured by the strain transient dip test technique in the heterogen eous dislocation structure consisting of cells or subgrains bounded by low-angle subboundaries. The structure is described by the two-compon ent model of hard and soft regions and the process of creep is conside red an iso-strain rate deformation process. An evolution of the intern al stress is derived from the evolution of dislocation structure chara cteristics in the normal primary creep and is evaluated for alpha iron from experimental data which were published earlier by the present au thor (Philos. Mag., 2-5 (1972) 865; 28 (1973) 891, 1099). As an illust ration of local conditions, local stresses and local strain rates are evaluated. The results document a growth of the mean internal stress i n creep and changes of local stresses in the hard and the soft region. The internal stress values are relatively low and do not approach the value found experimentally in the steady-state creep which reaches th e value of long-range internal stress in the soft region. A suggested interpretation of this discrepancy is based on an assumption that the actual steady-state creep has not yet been reached in the region of co nstant creep rate.