Abstract
A variational principle is proposed for the energy dissipation rate in two deformation modes in alloy-type Al--Mg solid solutions at high temperatures. For constant-stress creep the principle leads to the steady-creep law and a partial differential equation for the net dislocation-multiplication rate in nonsteady state. The solution to this equation gives the time development of dislocation density, from which the time development of creep strain is obtained. Fitting a theoretical creep strain vs time curve to an experimental one allows us to determine the relaxation time of creep and provides a method of measuring the average energy of a dislocation. For constant-strain-rate deformation, on the other hand, the principle leads to the steady-deformation law and another partial differential equation for the net dislocation-multiplication rate in nonsteady state. On the basis of the solution to this equation, a stress vs strain relation is obtained.
