Multiaxial mechanical equation of states for a work-hardening/recovery model of dislocation creep

Abstract

A model of creep has been proposed in which dislocation glide produces plastic strain and the number of gliding dislocations is determined by the competition between source operation, immobilization processes and recovery. Analysis of the model leads to a multiaxial mechanical equation of states, linking creep strain with time for a specimen subjected to any sequence of temperatures and principal stresses. The dislocation model exhibits the Lévy-Mises proportionality between deviatoric stresses and principal strain rates. In agreement with experimental data the constant of proportionality is predicted to be a function of temperature and of the second deviatoric stress tensor invariant, J. An algorithm that facilitates evaluation of the creep equation is presented together with parameter values which (comparison of prediction and experiment reveals) give a good representation of the creep of stainless steel. The new equation reduces, in the uniaxial case, to one which was earlier shown to agree well with data for creep under uniaxial stresses of variable magnitude and direction.