ABAQUS FEM ANALYSIS OF THE POSTBUCKLING BEHAVIOUR OF COMPOSITE SHELL STRUCTURES T. Möcker 1 , P. Linde 3 , S. Kraschin 2 , F. Goetz 1 , J. Marsolek 1 , W. Wohlers 3 1 Abaqus Deutschland GmbH, 52062 Aachen, Germany, E-mail: Torsten.MOECKER@3ds.com 2 Bishop GmbH - Aeronautical Engineers, 22587 Hamburg, Germany 3 Airbus Deutschland GmbH, 21129 Hamburg, Germany Keywords: postbuckling, FEM, crippling, failure load, damage model, fastener, cohesive behaviour Abstract For the design of stiffened composite shell structures the knowledge of the structural response in the postbuckling region is an important topic. Accordingly, tools are required that enable an accurate and reliable prediction of the postbuckling behaviour. In this paper it is shown how the finite element code Abaqus can be used for this purpose. When performing finite element simulations, a large amount of time is often needed to build up the finite element model - in particular if the model consists of several parts with complex geometries. For this reason the preprocessing tool Abaqus/CAE provides an interface which allows the user to automate repetitive tasks. Based on this interface, a tool simplifying the pre- and postprocessing of shell structures stiffened by stringers and frames was developed by Abaqus Deutschland for the company Airbus. Next to a summary of the abilities of this tool, the main focus of this paper is on discussing several modelling techniques that are used to enable a realistic idealisation of the physical problem and on presenting simulation results for an exemplary structure. Based on this example, the influence of modelling details like mesh density and geometric imperfections on the prediction of the failure load is discussed. 1 Generating the Finite Element Model In the design and development of aircraft fuselage structures, both theoretical analyses and experimental tests of the static behaviour play important roles in certification and technology processes. In particular, stiffened fuselage panels have to be analysed with respect to their buckling and postbuckling behaviour. Theoretical predictions have to be validated by a substantial number of experimental tests which are both expensive and utterly time consuming. To reduce the number of physical tests, finite element simulations of the test rig are carried out at the company Airbus with the code Abaqus. Since a large number of finite element models with similar geometries have to be built up, a graphical user interface (called SIMULPAC 1 - Simulation of Panels in Aircrafts) was developed using the core functionality of Abaqus/CAE. The programming language behind SIMULPAC is Python. SIMULPAC provides an automated design environment for the modelling and simulation of aircraft panels with different boundary conditions, e.g. with shear-compression test-rig conditions. The basic concept of SIMULPAC is to provide the user with all tools required to create a finite element model of a stiffened panel based on the parametric modelling principles of Abaqus/CAE in order to reduce the time for model generation significantly compared to the usual manual preprocessing. To achieve this goal, SIMULPAC extends the graphical user interface of Abaqus/CAE. E.g. a new model tree is added to the model and results tree already existing in Abaqus/CAE. This new tree guides the user through all steps required to generate the model of a stiffened aircraft panel (e.g. generation of stringers, frames, clips; definition of connectivity between structural parts). Within all of these steps, the user has to define the corresponding geometry based on predefined parameters which can be modified later on. Once the user has provided all of the required data, SIMULPAC generates the finite element model automatically. The final, generated model of a shear-compression test rig panel is shown in Figure 1. Subsequently, the user can add further features to the finite element model, which are not yet supported by SIMULPAC. Fig. 1 Model of shear-compression test rig panel generated by SIMULPAC