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Biaxial experiments with cruciform specimens are presented, and results compared with predictions of classical and recently formulated constitutive models on initial yielding, flow rules and subsequent yielding under multiaxial stress states. The cruciform specimen used showed very good strain homogeneity features compared to the commonly used cylindrical specimen. The equivalent flow curves at low and medium strain rate showed strain hardening and slight strain rate hardening. Furthermore, the case of symmetrical loading allowed for larger fracture strain and slightly higher flow curves. A deflection from the normality (i.e. non-associativity) of flow rule for plastic strain rate at the initial yield surface was observed. A directionality measure is proposed and applied in order to compare experimental results with theories. It appears that such a measure must enter the constitutive models of viscoplasticity. A preliminary calibration of the material functions entering the model given in Micunovic (1987), again for the case of a small strain range and a low strain rate, has been performed with a rough filtering of experimental data. The whole procedure should be extended to a large strain range and to cases of medium as well as high strain rate, to investigate the corresponding ranges of validity of the theories mentioned.

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Authors: ALBERTINI C, JRC Ispra Estab. (IT);MONTAGNANI M, JRC Ispra Estab. (IT);MICUNOVIC M, Svetozar Markovic University, Kragujevac (YU)
Bibliographic Reference: Paper presented: 10th International Conference on Structural Mechanics in Reactor Technology, Anheim Ca (US), Aug. 14-18, 1989
Availability: Available from (1) as Paper EN 34812 ORA
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