| Autor: |
Erhard Krempl, J.M. Gleason |
| Rok vydání: |
1996 |
| Předmět: |
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| Zdroj: |
International Journal of Plasticity. 12:719-735 |
| ISSN: |
0749-6419 |
| DOI: |
10.1016/s0749-6419(98)80002-8 |
| Popis: |
Two versions of the isotropic, small strain theory of viscoplasticity based on overstress (VBO) are given. They differ only in the dynamic recovery term of the growth law for the equilibrium stress. In the Yao formulation, this term is in the direction of the differences between the equilibrium and the kinematic stress deviators, two state variables of the theory. The inelastic strain rate determines the direction of this term in the Lee formulation. The predictions of the two formulations are compared in numerical experiments simulating proportional and nonproportional cyclic and monotonic loading. The two versions have the same material constants. They give identical results in uniaxial and proportional monotonic and cyclic loadings for a 6061 T6 aluminum alloy. They differ considerably when nonproportional loading is involved. In a strain controlled corner path the strees component corresponding to the strain that is held constant almost reaches zero at large strains in the Yao formulation. In the Lee formulation the stress is very different from zero. Also, the effective stress-strain diagram for the rectangular path ultimately joins the stress-strain diagram obtained in monotonic loading for the Yao model. A permanent difference remains for the Lee formulation. In cyclic 90° out-of-phase loading the hysteresis loops generated by the Lee model are much narrower than the ones predicted by the Yao version. The predictions of the Yao formulation are in good agreement with the results of biaxial experiments on the aluminum alloy. An analysis of the equations shows that differences between the predictions of the two formulations must be expected whenever unloadings are involved. The agreement in cyclic proportional loadings for the aluminum alloy is apparently due to the special material properties of this alloy. When material properties close to that of stainless steel are used a transient difference between the two formulations is found in cyclic proportional loadings. This experience suggests that models that predict the same behavior in monotonic loading may have vastly different responses in other loadings. Biaxial, nonproportional experiments and their numerical simulations are needed for the development of a reliable constitutive equation. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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