Thermoplastizitaet und Thermoviskoplastizitaet mit Schaedigung bei kleinen und grossen Deformationen

This report deals with the formulation and numerical integration of constitutive models with isotropic damage. Based on the irreversible thermodynamics and the internal state variable theory, damage-thermoplasticity and -thermoviscoplasticity models incorporating nonlinear isotropic and nonlinear kinematic hardening are presented. Care is taken that the evolution equations governing the hardening response satisfy the second law of thermodynanmics in the form of the Clausius-Duhem inequality for every admissible process. For three elastoplastic damage models, a possibility to generalize the constitutive equations from small to finite deformations is shown. A damage evolution equation for ductile damage is formulated taking into account the nucleation and growth of voids. The generalization of the constitutive equations to finite deformations is based on the concept of so-called dual variables. The characteristic features of the theoretical framework adopted, are the choice of the strain and stress tensors and suitable associated time derivatives as well as the modeling of the kinematic hardening. In view of an efficient numerical integration procedure, small elastic strains and a simplified kinematic hardening rule is assumed. For this simplified version of the consitutive models some restrictions must be fulfilled in order to satisfy the Clausius-Duhem inequality in a sufficient way. For a simplified version of a damage-thermoviscoplasticity model an efficient, implicit time integration algorithm making use of the operator splitting methodology is presented. The special structure of the system of differential equations allows a reduction of the equations to be solved by means of Newton's method. The contributions to the consistent tangent modulus are calculated analytically. The resulting integration algorithm has been implemented as a UMAT-subroutine into the ABAQUS finite element code. Some numerical examples for displacement and force controlled processes are discussed. Based on a coupled thermomechanical FE analysis, the necking of an axisymmetric tensile specimen and the deformation behavior of a thin cylinder under internal pressure and thermal loading is simulated. (orig.)Available from TIB Hannover: ZA 5141(6053) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman