Development of a Variant of Scalar Constitutive Equations Suitable for Description of the near Super-Plastic Regimes of Deforming

When deformations are carried out with fine grained microstructure and within a narrow range of strain rates and temperature, metals and ceramics have been shown to exhibit superplastic behavior. Under these conditions the material demonstrates unusually high elongation with a relatively stable microstructure. But when the above mentioned parameters lie beyond a limit, near superplastic behavior is observed. The microstructure changes actively during the process of deformation and the response of the material becomes dependant on the history of loading. A model to describe the dependence on loading history by taking into account the change in microstructure is proposed. The model predicts the general trends observed and also provides possible explanation to some of the effects observed in the experimental data.