@article{khraisheh_zbib_hamilton_bayoumi_1997, title={Constitutive modeling of superplastic deformation .1. Theory and experiments}, volume={13}, ISSN={["0749-6419"]}, DOI={10.1016/S0749-6419(97)00005-3}, abstractNote={In this work, we investigate the mechanical behavior of superplastic materials under various loading conditions and examine the nature of anisotropy. This and other phenomena are modeled within a continuum theory of viscoplasticity which includes an overstress function, ‘yield surface’ and internal variables. Anisotropic hardening is represented by an internal stress tensor whose evolution (including plastic spin) consists of hardening, dynamic recovery, and static recovery terms. The ‘dynamic’ yield surface (within a viscoplasticity formulation) is assumed to be isotropic and depends on both J2 and J3. Various experiments on a PbSn superplastic alloy including tension, jump test, stress relaxation, fixed-end torsion, and combined tension-torsion tests were performed and the results are used to calibrate and verify the theoretical model. It is shown that the isotropic dynamic surface can successfully model the uniaxial behavior of superplastic deformation, including stress relaxation, and produces axial stresses in fixed-end torsion.}, number={1-2}, journal={INTERNATIONAL JOURNAL OF PLASTICITY}, author={Khraisheh, MK and Zbib, HM and Hamilton, CH and Bayoumi, AE}, year={1997}, pages={143–164} }
 @article{ding_zbib_hamilton_bayoumi_1997, title={On the stability of biaxial stretching with application to the optimization of superplastic blow-forming}, volume={119}, ISSN={["0094-4289"]}, DOI={10.1115/1.2805969}, abstractNote={The instability of biaxial stretching of thin sheets of viscoplastic metals under plane stress conditions is investigated using a linear stability analysis. An instability criterion for biaxial stretching is developed based on the assumption that localized necking initiates along the direction perpendicular to the major principal stress direction. Various “optimum” variable strain rate paths, which ensure a stable deformation of the sheet without neck formation, are computed for different strain ratios based on the instability analysis. The variable strain rate paths are applied in the finite element modeling of the superplastic uniaxial extension of a tabular specimen and supe´rplastic blow-forming of a hemisphere. A reduction of forming time is achieved compared with the established constant strain rate forming method, while uniformity in the thickness distribution of the formed parts are maintained.}, number={1}, journal={JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY-TRANSACTIONS OF THE ASME}, author={Ding, XD and Zbib, HM and Hamilton, CH and Bayoumi, AE}, year={1997}, month={Jan}, pages={26–31} }