Multimodel Numerical Analysis of the Elasto-Visco-Plastic Deformation of Materials and Constructions Semenov A.S., Melnikov B.E. St.-Petersburg State Technical University, Russia. 1. Introduction The increasing demands for reliability and durability of structures with simultaneous material economy have stimulated improvement of constitutive equations for description of inelastic deformation processes. This has led to the development of phenomenological modeling of complex phenomena of irreversible deformation including history-dependent and rate-dependent effects. During the last several decades many works have been devoted to the development of plastic and viscoplastic models, in order to better predict the material behavior under combined variable thermomechanical loading. There are more than the ten theories of viscoplasticity and their modifications. Among the possible explanations of observed diversity of models can be pointed out on the two reasons of fundamental and applied character. The first cause is connected with variety of viscoplastic prop- erties manifestation, reflecting diversity of physical micromechanisms of inelastic deformation. The second reason is brought about variety of requirements in complexity and accuracy for real engineering applications. The results of various viscoplastic models predictions often are considerably differed from the experimen- tal data in some cases of the non-proportional loading. Therefore the problem of choice of the more suitable theory of plasticity is actual for the strength analysis of structures under combined loading. The suggested multimodel approach, which is based on the creation of hierarchical consistency of the models, whose fields of reliable appli- cation partially coinciding mutually supplement each other, is most rational. Application of the concrete model must correspond to the complexity of being considered loading processes. The developed strategy of multimodel analysis consists of the following features: • creation of the plastic and viscoplastic models library, providing solution of the wide spectrum of non-elastic problems, • determination of the selection criteria system, realizing the choice of the simplest variant of theory sufficient for correct problem solution, • caring out of multivariant sequential clarifying computations. Computation with using of several different theories should be performed in the most responsible cases of strength analysis. Coincidence of the results according different models demonstrates the correctness of computa- tions. Difference between obtaining results for structure demands determination of the most adequate model. This choice can be carried out on the base of comparison between numerical results and experimental data for more simple geometrical object - element of material, subjected to the same history of loading as the most stressed point of structure. The basic ideas and application of multimodel analysis for the rate-independent material behavior was described in previous work of authors [1-3]. Present analysis is devoted to rate-dependent deformation. 2. Library of plastic and viscoplastic models The developed library of material models represents generalized data set, including information about limitations on field application, basic experiments for material parameters determination, continuous mathematical model, discrete numerical model, computational algorithm, implementation into finite element program, recom- mendations about computation strategy. The set of following criteria has been taken into consideration: − conformity to a general principles of physics (thermodynamic laws, principle of determinism, principle of fading memory, principle of local action, tensorness of all relations and others), − experimental verification of models for various classes of loading, − possibility of micromechanical interpretation, − complexity of determination of the material parameters, − algorithmic effectiveness. 2.1 Plastic models