There has been an increased interest in the mechanics and materials field to improve constitutive relations for the superplastic deformation of advanced materials. This interest has been stimulated due to the discovery of high strain-rate superplasticity and the development of new micromechanical characterization techniques. In this paper, an attempt was made to develop a unified phenomenological model which accounts for deformation at both very high and very low strain-rates. Although the model is an extension of an earlier mechanistic model by Hart for superplasticity, it incorporates detailed microstructural parameters. It can also be extended to multiaxial deformation. Using the model, the deformation mechanisms in superplastic Al-7475 were explained. Load relaxation and strain-rate change tests were employed in this investigation. Microstructural characterization was carried out by optical microscopy and Orientation Imaging Microscopy (OIM).
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