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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 91
PROCEEDINGS OF THE TWELFTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping, L.F. Costa Neves and R.C. Barros
Paper 203

Finite Element Stability Analysis of Damaged Composite Shell Structures

W. Wagner

Institute for Structural Analysis, University of Karlsruhe (TH), Germany

Full Bibliographic Reference for this paper
W. Wagner, "Finite Element Stability Analysis of Damaged Composite Shell Structures", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 203, 2009. doi:10.4203/ccp.91.203
Keywords: stability analysis, composite material, damage, shell structures, finite element modelling.

Summary
This paper presents an approach for the stability analysis of stringer-stiffened fibre reinforced polymer panels under axial compression based on the finite element method. In the first part we discuss the necessary modifications of shell formulations to model layered shear-elastic thin shell structures allowing for an arbitrary stacking sequence and furthermore a variable position of the reference plane along the thickness. A main goal of the paper is the modeling of damaged structures. Here intralaminar and interlaminar damage may occur. Different ply discount models with constant knock-down factors are employed to account for ply failure which can occur as fibre fracture, matrix cracking, or fibre-matrix shear failure. Finally a modified material law using so called knock-down factors is derived. The interlaminar damage, here especially delamination of layers and particularly debonding of stiffeners from the skin of stiffened panels, is modeled via so-called two- or three-dimensional interface elements in which a cohesive zone approach is implemented. Material laws for the cohesive zone are discussed and a special exponential cohesive law is presented which is history-dependent in order to prevent restoration of cohesion. The interpenetration of the crack faces is avoided using a penalty contact formulation. The algorithms developed are applied to two examples were experimental data are available. The first example presents the simulation of axial compression tests for single-stiffener panels whereas the second example shows the simulation of a curved multi-stiffener panel again under axial compression. The pre- and post-buckling response of these composite structures are calculated with an arc-length as well as dynamic solution algorithms in case of multi-buckling. The response of the structures is governed by the complex intra- and inter-laminar damage behaviour. The performance and applicability of the proposed models are described in detail and the results are compared to the experiments.

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