JEC COMPOSITES MAGAZINE - Issue #48 - May 2009 - 40

FEATURE “Aeronautics” An industrial solution to simulate post-buckling and damage The SAMCEF finite-element code provides solutions for modelling and analysing post-buckling in composite structures. Post-buckling results in large transversal displacements, which means that a reliable non-linear procedure is required. Ply and interface degradation models can be used to more accurately predict the complex structural behaviour of the composite structure up to the final point of collapse. This paper presents the numerical results obtained as part of research conducted under the COCOMAT European project. Comparison with experimental results shows that SAMCEF accurately predicts the damage mechanisms, panel behaviour and collapse load. 1 2 3 1- MICHAËL BRUYNEEL, R&D ENGINEER, SAMTECH S.A., 2- RICHARD DEGENHARDT, PROFESSOR, DLR GERMAN AEROSPACE CENTER AND PFH GÖTTINGEN 3- JEAN-PIERRE DELSEMME, SENIOR R&D ENGINEER, SAMTECH S.A. The COCOMAT European project Composite materials are increasingly used in modern aeronautical structures. Complex structural analyses are required to help reduce part weight, exploit reserves and propose safe designs. Advanced simulation tools are useful for identifying new design scenarios, bringing the ultimate and collapse loads as close together as possible to improve the operating range of the structural components (Figure 1). COCOMAT is a European project that started in 2004 and ended in 2008. The goal of this project was to develop improved, reliable procedures to quickly analyse post-buckling and collapse in stiffened fibre composite panels intended for future fuselage structures, while taking material degradation into account. Fig. 1: Current and future design scenarios for typical stringer-stiffened composite panels. SAMCEF for non-linear analysis of composite panels SAMCEF Mecano is an implicit finite-element code that can take into account large deformations, large displacements and large rotations. Over the years, it has proved efficient in simulating post-buckling structural behaviours with either a static or dynamic solution procedure. Three main modes of failures can appear in composites: delamination, matrix cracking and fibre breaking. Delamination is an inter-laminar failure which results in the separation of adjacent plies. This phenomenon appears close to holes, plydrops, free edges, or more generally in regions where a threedimensional state of stress exists. Cohesive element models are available in SAMCEF to simulate this effect. For intra-laminar failures, such as matrix cracking and ply breaking, a specific material model has been developed. This model can predict fibre-related damage, as well as damage in the transverse and shear directions of the matrix. Non-linearities can also be introduced in the fibre direction. Finally, this model can be coupled to plasticity with isotropic hardening. Industrial test case A stiffened composite panel subjected to compression was considered in this industrial case. Figure 2 shows both the physical prototype and the finite-element model. The non-linear procedure in SAMCEF was used to identify the equilibrium path 40 jec composites magazine / No48 May 2009

JEC COMPOSITES MAGAZINE - Issue #48 - May 2009

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