A MODEL OF INTERNAL-STRESS SUPERPLASTICITY BASED ON CONTINUUM MICROMECHANICS

A new theoretical model is proposed to explain internal stress superplasticity under a simultaneous applied stress during thermal cycling. The analyzed material is an elastically uniform body containing an elastic spherical inclusion, surrounded by a plastic matrix obeying a power law creep. It is assumed that only relaxation by interface diffusion is significant. At first it is shown that an inclusion dilatation can be counterbalanced by a certain matrix plastic flow. Assuming a certain stress distribution for this condition, a stationary flow on heating or cooling results. Typical behavior of this stationary flow is analyzed for the specific cases of high or low applied stresses. Under a low applied stress, the internal stress by an inclusion dilatation strongly accelerates the flow in the direction of the applied stress, which is in proportion to the applied stress, to the heating or cooling rate and to the inclusion volume fraction.