A Two Scale Finite-Element-Approach to Analyse the Damage State of Composite Structures

Fibre reinforced composite materials offer a great potential for the development of lightweight structures. The exploitation of the material properties therefore demands the development of smarter and more powerful constitutive models to take into account all constitutive effects of interest. The investigation of the damage and fracture behaviour of composite materials is of scientific interest for more than 120 years. But until today there exists no theory which captures all of the significant features of composite materials at multi axial loading conditions in a sufficient way. In fact, there exists a number of theories applicable for several special loading conditions. In this work a two scale finite element model is developed to describe and analyse the anisotropic damage state of fibre reinforced composite materials. The thermodynamically consistent formulation is based on the standard continuum mechanics framework of finite deformations. The damage onset is measured by means of the maximum principal stress criterion of the true Cauchy stress tensor. The corresponding eigendirection is used as the crack propagation direction. The coupling of the macro scale and the micro scale is carried out by means of the UMAT utility of the commercial finite element system Abaqus. A shell with a concentric hole is used to verify the two scale approach and to show the mesh independence of the finite element solution. Afterwards a class of newly developed crimped end fittings is analysed to show the applicability of the two scale approach on complex models, too