Indexed on: 01 Mar '79Published on: 01 Mar '79Published in: Journal of Materials Science
The main results of stress drop experiments during high temperature creep (i.e. the occurrence of zero and sometimes negative creep rates, the existence of two parts with different slopes in the curves of the incubation time Δtr versus the stress decrement Δσ, the zero or positive values of the stress variations in stress relaxation tests) are analysed from a rheological point of view. The basis of the proposed interpretation is the existence of a creep criterion, represented by a limit surface in the stress space, which explains through the usual plastic flow rules the occurrence of zero or negative creep rates. The work hardening splits into a translation (kinematic hardening) and a deformation of this limit surface. The recovery of kinematic hardening is slower than the recovery of deformation. On this basis, the concept of internal stress used either in the activated glide of dislocations or in the Bailey-Orowan relationship and the nature of negative creep rates are discussed.