An improved analysis model for material nonlinearity induced by elasto-plastic deformation and damage including large strain response was proposed. The elasto-plastic-damage constitutive model based on the continuum damage mechanics approach was adopted to overcome limitations of the conventional plastic analysis theory. It can manage the anisotropic tensorial damage evolved during time-independent plastic deformation process of materials. Updated Lagrangian finite element formulation for elasto-plastic damage coupling problems including large deformation, large rotation and large strain problems was completed to develop a numerical model which can predict all kinds of structural nonlinearities and damage rationally. Finally a finite element analysis code for two-dimensional plane problems was developed and the applicability and validity of the numerical model was investigated through some numerical examples. Calculations showed reasonable results in both geometrical nonlinear problem due to large deformation and material nonlinearity including the damage effect.
Nonlinear behavior of a structure can be separated into material and geometric nonlinear effects. Geometric nonlinearities has been set theoretically and numerical algorithms are being improved continuously. A constitutive relation which globally represent material nonlinearities due to molecular bindings, polycrystalline structures, and other micro-level characteristics of a material has been a crucial interest to modem researchers. Continuum damage mechanics(CDM) proposed by Kachanov (1958) has shown that damage, similar to strain, can be a measure of characterizing material responses, and thus can be treated as an internal state variable. Continuum damage is considered as an average density of microcracks or microvoids over a certain volume in a body. Nonlinear responses of a material can be correctly described using the damage concept. Since late 1980s, lots of researches have been successful in developing rational CDM model and its applications to engineering fields. Among them is an analysis of a welded tubular joint of offshore platforms (Jubran and Cofer, 1991).
