Overview
New, super-efficient aircraft require new, advanced materials; therefore the development of a new generation of Fibre Metal Laminates (FML) and Metal Laminates (ML) is necessary. These new laminates should provide significantly improved strength and stiffness properties for tailored fuselage applications. It is necessary to develop material models and static failure criteria for the prediction of the material behaviour of FML and ML, in both the microscopic and the macroscopic scale, for easier design with these new laminates.
The fatigue properties of these innovative laminates, which were not yet available, were required to match those of the rather expensive GLARE® material. The objective was to attain a significantly increased static behaviour and a well-balanced combination of mechanical properties. The high manufacturing costs of FML would be reduced by using less expensive material systems, such as high performance ML.
The technological objective was a fuselage skin weight reduction of up to 30% when compared to GLARE‚. This was made possible to be achieved by an increase in static properties. The strategic objectives were to obtain an increase in the operational capacity of 10%, a reduction in the direct operating costs of 10% and finally a reduction in fuel consumption of 10%, thus reducing the environmental impact with regard to emissions and noise. The strategic and economic objective is a reduction in the product cost of 5% derived from a material cost reduction of 20%.
The expected result was a material with significantly increased static behaviour and a well-balanced combination of mechanical properties, accompanied by a reduction of manufacturing costs of FML and a fuselage skin weight reduction. There would be an increase in operational capacity, a reduction in direct operating costs, a reduction in fuel consumption and thus a reduced environmental impact with regard to emissions and noise.
New fibre metal laminates and metal laminates that provide significantly improved strength and stiffness properties for tailored fuselage applications would be developed. This was possible to be achieved by the use of alternative constituents such as new fibres, advanced metals and modified pre-preg systems. The mechanical and fatigue properties of the newly developed materials were tested, as well as the production process, which included pre-treatment and bonding. It could be investigated if existing joining concepts are suitable for the new laminates but the manufacturing costs of FML could be reduced by using less expensive material systems such as high performance ML.
Appropriate manufacturing and joining technologies required validation for the progressive laminates. Corrosion was a problem to be quantified and resolved with new sizing and treatments. Material models and static failure criteria for the prediction of the material behaviour of FML and ML in both the microscopic and the macroscopic scale would be developed and verified. Finally, optimisation criteria for the design of coupons and structural elements would be developed and experimentally verified for laminates with the aim to reduce the overall weight of the aircraft fuselage.
Funding
Results
Experimental and numerical activities were developed to investigate the behaviour of Fibre Metal Laminates (FML) shear loaded panels with a bonded window frame. Both static and fatigue tests were carried out at the Department of Aerospace Engineering of Pisa on 10 panels manufactured by Alenia Aeronautica. In addition to technological problems, the tested specimens represent very critical components, involving fundamental aspects of the structural design of fuselage panels; in particular, the primary interest to exploit the post buckling behaviour of FML components, as commonly applied in conventional aluminium alloy fuselage structures, is associated with the effort of making reinforced holes which do not alter significantly the stress distribution of the main body of the panel. Detailed finite element analyses, performed by means of the ABAQUS V 6.5 package, have been used to investigate the panel response during testing. The numerical results have shown a very good agreement with the experimental data, thus revealing an effective instrument to study the behaviour of a post buckled shear panel, in presence of the neutral hole issue.