THE BACK STRESS CONCEPT IN POWER LAW CREEP OF METALS - A REVIEW

The idea that the plastic deformation of crystalline solids takes place under only a part of the applied stress and not under the entire stress is used to discuss the well-known discrepancy between the natural third-power dependence of the steady state creep rate on the applied stress and the experimentally observed significantly stronger dependence in metals and solid solution alloys exhibiting metal class behavior. The back stress is identified with the internal stress measured by a dip test technique and introduced into the third-power law creep equation. Some results of the complete unloading experiments in steady state creep as well as the results of internal stress measurements during backward straining after the complete unloading are presented and discussed on the basis of the model of soft and hard regions of dislocation structure.