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A sigmoidal model for superplastic deformation

Pan, W. and Krohn, K. and Leen, S.B. and Hyde, T.H. and Walloe, S. (2005) A sigmoidal model for superplastic deformation. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 219 (3). pp. 149-162. ISSN 1464-4207

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A new phenomenological model, designed to capture the sigmoidal nature of stress dependency on strain rate for superplastic deformation, is presented. The model is developed for the Ti-6Al-2Sn-4Zr-2Mo alloy using data obtained under controlled strain-rate tensile tests spanning a range of strain rates and temperatures, from 930 to 980 °C. The sigmoidal model performance is compared with that of a more conventional double-power law, strain, and strain-rate hardening model using time-dependent finite element and theoretical analyses. The primary intended application of the sigmoidal model is for more accurate simulation of the effects of strain-rate variation within test specimens and sheet during superplastic deformation. Analysis of this variation within two designs of tensile test specimens is presented to illustrate this aspect.