Numerical Method For Thermo-viscoplastic-damage Constitutive Relation And Research On Dynamic Response Of Al-Li Alloys

This paper is correlative with "Research on stress wave propagation characteristics and spallation criterion of Al-Li Alloys under combined impact loadings" which is supported by the National Nature Science Foundation of China (10272097). Because of their special impact ductility and good high-temperture bearing propeterities, the Al-Li alloys have been getting into wider and wider uses as a primary material in the field of spaceflight and avigation. This paper has carried out the research on the dynamic mechanical behavior and properties of AL-LI alloys by the experimental, theoretical and numerical ways. The paper mainly include: thermal-mechanical-rate-damage coupling dynamic constitutive relation, high pressure state equation, the damage evolution equation and the spallation criterion, numerical simulations and combined stress wave propagation rules.About constitutive relation and numerical method. Firstly, on the modified Drucker's postulate and theory of internal variables in the constitutive relations, the universal form of the damaged thermo-visco-plastic incremental constitutive relations and the computational routine are established. This constitutive relation can cover various kinds of plastic hardening (softening) behaviors, thermo-softening behaviors, damage-softening behaviors and their coupling effects between each other. Secondly, a strictly theoretical testification of the better method of radius regression is given. Thirdly, this paper has researched into the thermal-mechanical-rate-damage coupling propeties of Al-li alloys under combined impact loadings. Especailly the limit strain rate softening effect(negative sensitivity of the materials to strain rate) is found, and the scientific concept of the limit strain rate softening is presented. Lastly, We have established the high pressure state eqution and dynamic constitutive relation with limit strain rate softening and temperature softening effects.About the damage evolution equation and the spallation criterion. We present a new kind form of damage evolution equation by the method of phenomenological analysis and microscopic statistics, and on the basis of this we have established several spallation criterion that is used easily in engineering. We present a method by which the damage evolution equation and the spallation criterion can be established by the combination of experiment, theory and numerical simulations. With our method the damage evolution equation and spallation criterion of Al-Li alloys has been estabished. By the numerical simulations of the free surface velocity histories...