Nichtlineare Versagensanalyse von Faserverbundstrukturen

The present thesis is concerned with the numerical simulation of nonlinear behavior in composite structures by means of the Finite Element method. Thereby special attention is payed to nonlinear material behavior. For this phenomenological material models are developed and presented, which are capable of describing the overall structural response including local effects like delaminations. After the presentation of an anisotropic plasticity model combined with anisotropic hardening the frequently observed and very dangerous type of failure delamination is considered in particular. On the basis of a multilayered, three-dimensional oriented shell theory including higher-order displacement kinematics across the thickness first-ply-failure indicators available from literature are presented at first. They are compared among themselves in particular with respect to their use as yield criterion or damage criterion in a materially nonlinear analysis. In what follows the anisotropic Hoffman failure criterion is used in the context of a plasticity formulation. Thereby an anisotropic hardening law is included allowing to simulate a nonlinear anisotropic hardening response of the laminate. In order to study the impact of the anisotropic hardening plasticity model structural examples are compared and assessed. For their simulation the progressing delaminations are described in this thesis in a smeared manner and not as a geometrical discontinuity. Due to this continuum mechanics based description it is possible to represent delamination within a thin process layer. Hence four different material models are developed and presented. Some are formulated in the context of a softening plasticity theory while others are formulated in the context of continuum damage mechanics. All models in common is, that they use the critical fracture energy within the description of softening material response. Using those models in combination with a standard continuum mechanics approach leads to the well known problems of mesh sensitivity and loss of ellipticity of the underlying partial differential equations. In order to overcome these problems a mesh adjusted softening modulus is used and moreover a visco-plastic respectively visco-damage regularization is applied where required. In case of the delamination plasticity model the viscosity parameter is adapted automatically with the objective of minimal effect on numerical results. In contrary the delamination damage models utilize a constant viscosity parameter. Both plasticity and some damage models employ the Brewer-Lagace criterion in its original or modified form as yield or damage criterion, respectively. Additionally a further delamination damage model is developed, which has some similarities to the model proposed by Ladeveze and co-workers. It uses the definition of an equivalent energy release rate as damage criterion.SIGLEAvailable from: http://deposit.ddb.de/cgi-bin/dokserv?idn=967942187 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman