Stability approach to testing the constitutive relations of superplasticity

An approach to testing the suitability of the constitutive relations for describing superplasticity is proposed based on an analysis of the stability conditions of uniform extension of samples with respect to small perturbations of the current configuration. The necessity of accounting for the partial preservation of the local topology in varying the equations of motion is shown using a simple (nonlinear viscous) model of a superplastic medium.