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== Abstract ==

Rib or grid stiffened structures have been investigated for decades, mainly for
application in space structures.
Grid structures offer the possibility to develop more damage tolerant structures as the
network of ribs can provide redundant load paths. In an ideal situation, an aircraft fuselage
could have a load carrying grid with ribs that carry tensile, compressive and shear loads. The
skin would only need to sustain the cabin pressure load.
Such a configuration could lead to significant weight reduction as a different design
philosophy can be used. Typically, a damage tolerant design approach allowing a maximum
of 3000 µstrain is used for composite aircraft structures. Using a grid structure, a different
approach could be developed for a design which could allow strains up to 6000 µstrain.
Automated fibre placement has made composite grid structures an affordable option.
However, they pose a major challenge in the development of tooling for cure due to their
complex and sometimes irregular structure.
Within the European funded Horizon 2020 ACASIAS programme, square antenna elements
are developed to be integrated in a composite aircraft fuselage panel. For this reason, an
orthogrid stiffener pattern was chosen. As the skin of the panel must be transparent for the
antenna signals, a glass fibre skin is required. A glass fibre skin to carry shear loads and
carbon fibre ribs to carry compression and tension loads is therefore being developed to be
able to meet structural and electromagnetic requirements.
This paper describes aspects of the ongoing development for the design, manufacture and
testing of an orthogrid stiffened structure in an efficient way.
Simple alternating cutting of tapes at the crossing appear to be a suitable solution with a
tensile stiffness reduction of 10 % compared to the situation without cuts. These and other
details and elements are tested to validate the final design.
The use of reusable silicone vacuum bags was investigated in order to replace complex
metal tooling blocks. Besides saving on mould materials and machining, the use of a preshaped silicone vacuum bag is expected to reduce labour cost due to a decrease in handling
of tooling blocks for positioning and cleaning.
The first trial indicates that good quality laminates can be obtained using reusable vacuum
bags. More testing will be carried out to validate the concept for a large 3×1.2 m panel.

== Full document ==
<pdf>Media:Draft_Content_956111276-p20-9299-document.pdf</pdf>

== References ==

[1] H. Schippers et al., “Broadband Conformal Phased Array with Optical Beam Forming for Airborne Satellite Communication”, IEEE Aerospace Conf., March 2008, Big Sky, MT, USA.

[2] S. Panthi, J. King, and C. McLain. "The eXConnect Broadband Aeronautical Service", 31st AIAA International Communications Satellite Systems Conference (ICSSC), (AIAA 2013-5621), October 14-17, 2013, Florence, Italy. [https://doi.org/10.2514/6.2013-5621 https://doi.org/10.2514/6.2013-5621]

[3] ACASIAS web site at [http://www.acasias-project.eu/objectives-and-innovations-11 http://www.acasias-project.eu/objectives-and-innovations-11], Accessed 21 March 2019.

[4] Steven M. Huybrechts, Steven E. Hahn and Troy E. Meink, “Fabrication, analysis and design methods”, ICCM12 Conference, Paris, July 1999, paper 357 , ISBN 2-9514526-2-4

[5] J. M. Müller and W. van den Brink, “Comparison of integrated rib stiffened and L-blade stiffened composite panels manufactured using simple tooling methods,” in SAMPE Technical Conference, Long Beach, USA, 2016.

[6] Michael P. Kleiman, “Light carbon-fiber structure protects heavy space cargo”, AFRL Space Vehicles Directorate, February 26, 2007. Available at: [https://www.wpafb.af.mil/News/Article-Display/Article/401406/light-carbon-fiber-structure-protects-heavy-space-cargo/ https://www.wpafb.af.mil/News/Article-Display/Article/401406/light-carbon-fiber-structure-protects-heavy-space-cargo/] Accessed 21 March 2019.

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Scipediacontent: Scipediacontent moved page Draft Content 956111276 to Muller Nijhuis 2020a

Scipediacontent: Created page with " == Abstract == Rib or grid stiffened structures have been investigated for decades, mainly for application in space structures. Grid structures offer the possibility to deve..."