Homogenization of two-phase elasto-plastic composite materials and structures - Study of tangent operators, cyclic plasticity and numerical algorithms

We develop homogenization schemes and numerical algorithms for two-phase elasto-plastic composite materials and structures. A Hill-type incremental formulation enables the simulation of unloading and cyclic loadings. It also allows to handle any rate-independent model for each phase. We study the crucial issue of tangent operators: elasto-plastic (or "continuum") versus algorithmic (or "consistent"), and anisotropic versus isotropic. We apply two methods of extraction of isotropic tangent moduli. We compare mathematically the stiffnesses of various tangent operators. All rate equations are discretized in time using implicit integration. We implemented two homogenization schemes: Mori-Tanaka and a double inclusion model, and two plasticity models: classical J(2) plasticity and Chaboche's model with non-linear kinematic and isotropic hardenings. We consider composites with different properties and present several discriminating numerical simulations. In many cases, the results are validated against finite element (FE) or experimental data. We integrated our homogenization code into the FE program ABAQUS using a user material interface UMAT. A two-scale procedure allows to compute realistic structures made of non-linear composite materials within reasonable CPU time and memory usage; examples are shown. (C) 2002 Elsevier Science Ltd. All rights reserved.