How to promote the development of composite structural applications in the future?

Many business entities and aerospace partners of the European Aerospace Defense Group (EADS) are actively involved in the development of more environmentally friendly and cleaner commercial aircraft. They are actively seeking to bring sustainability to aircraft design through a global network of technical competence centers, collectively known as EADS Innovation Works, to explore each component individually.
Sustainable Aircraft Design Dr. Tamas Havar is an expert at EADS InnovationWorksite near Munich, Germany, where he is responsible for various projects in the Structural Integration and Mechanical Systems division. He and his team are responsible for developing new aircraft structures that use composite materials. Havar said: "Our ongoing analytical program aims to focus on developing innovative composite design and manufacturing methods that reduce displacement and manufacturing costs."
As part of the German Federal Ministry of Economics and Technology's Aviation Research Program “LuFo IV-HIT”, the Airbus High-LiftR&T team leads from different EADS business units and universities.
In automotive applications, reinforced carbon fiber (CFRP) prepregs are often the preferred composite. In this case, however, the EADS engineering team chose a non-autoclave molding process that required the use of textile composites while considering cost reductions. In addition, textile composites are also used in A380 pressure bulkheads, the A380 is the most used composite material for Airbus to date.
A key factor in designing a composite aerospace structure is how the components are connected to the surrounding aircraft structure. Current composite high-lift structures such as flaps are usually connected to the wing by a metal load-introducing structure. These structures that provide fail-safe design can result in increased body weight and increased manufacturing costs. In addition, there is also a difference in thermal coefficient between the metal and the joined composite part. On the other hand, composite load-introducing structures also allow for damage tolerance design because one layer of breakage can be compensated for by other good layups. In addition, the use of composite materials eliminates the problem of thermally conductive loads because both high lift and load-introducing structures use the same composite material.
Development of Abaqus FEA Propulsion Composite Structure Analysis The EADS Innovation Works team selected Abaqus FEA for design analysis of its composite LIR. “Abaqus is our preferred nonlinear solver. It has powerful composite analysis capabilities and is particularly well suited for analyzing 3D units such as those involved in our LIR studies.” Abaqus FEA can be used throughout the EADS product design lifecycle, Havar said. Process. The concept phase can be used to narrow down the design, which can be used to design preferred concepts during the preliminary design phase and to ensure that all specifications are met during the final or detailed design phase.
The new composite LIR includes not only drive ribs that provide integral lugs, but also rivets that secure the assembly to the flap skin. The team's goal was to simplify the complex geometry preforming of LIR to ensure consistent thickness in addition to preforms that were relatively simple and low-cost, reducing manufacturing costs. The team's solution was to automate pre-formed placement with LIR profiles to minimize manufacturing costs.
To model a new design, the EADS team had to consider the complexity of the composite structure, including thickness variations ranging from 4 to 10 mm, additional resin at the sag and chamfer, and lining at the fillet. Havar pointed out: "In consideration of the composite's own variables, we should use 3D units to calculate composite load introduction and accurately analyze all stress components. Since composite load introduction often occurs delamination problems, we must pay attention to lateral shear And peeling stress."
Taking into account the above factors, the EADS engineering team constructed the LIR model using a variety of different Abaqus components. In the case of flaps, they used about 20,000 2D units, and for the LIR itself to calculate the load introduction, they used about 100,000 continuous shell 3D units, including composite layup hexahedral units (each unit 4 ~8 layers, each layer has anisotropic properties, support 3D component orientation) and pentahedral cells where the layer is depressed. The isotropic property is applied to the resin matrix. In summary, the LIR model provides approximately 450,000 degrees of freedom (DOF).
In addition, the engineering team must demonstrate the 324 rivets used in the assembly to secure the LIR to the surrounding structure and withstand the load. Havar pointed out: "This depends not only on the structure being fixed, but also on the rivet material and its dimensions." To achieve this, each rivet is modeled using an elastic connector between the components. On one side, the rivets are attached to the composite flap skin and the other side is secured by a multi-point constraint (MPC) to distribute the load across different skin thicknesses. The connection load obtained by the analysis is used to calculate the safety factor of the skin extrusion and the safety factor of the rivet fracture.
To complete the LIR analysis, the EADS team also calculated some load cases using the Abaqus implicit solver and post-processing. In the above scenario, the flap is fixed at the boundary of the beam element to simulate three translational degrees of freedom at the end under simulated test conditions. For some load cases, the beam elements on the outside end are symmetrically translated, creating additional torque on the flaps. The analysis yielded intra-layer failure (in composite layup) and inter-layer effectiveness (between laminates) as well as rivet and lug load results.
Positive results of composite analysis If composites are important for designing future environmentally friendly, cleaner and sustainable aircraft with lighter weight, higher fuel efficiency and less displacement, then EADS composite analysis The results have had a positive impact on all aspects. For LIR, the in-plane and lateral stress components are within the design tolerance of the new composite; for all rivets, the strength coefficient of performance for connecting the LIR to the surrounding structure is up to standard or exceeding the standard; for composite lugs In other words, performance is also within the scope of industry safety regulations.
ADS hopes to integrate more composite structures in aircraft design, so there is no doubt that the Innovation Works Lightweight Design team will be busy with a range of FEA projects. As design engineers and FEA software developers work together to address analytical challenges, composite materials are bound to become an important part of more environmentally friendly new aircraft. I believe that you will board such a flight in the near future.

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