Colloquiam: I European Conference On Multifunctional Structures (EMuS2019), June, 11-12, 2019

Analysis of Radar Absorbing FSS on Foldcores and Honeycombs

Scipedia content — Thu, 04 Mar 2021 08:55:25 +0100

The objective of the paper is to investigate the radar absorption of honeycombs and
foldcores with printed conductive patterns. These structures can be manufactured by first
printing conductive Frequency Selective Surfaces (FSS) on planar substrates, which then can be used to shape foldcores and honeycombs by means of specific manufacturing technologies.
Foldcores can be considered as intermediate shapes between planar sheets (where the printed
patterns are perpendicular to the impinging radar waves) and honeycombs (where the printed
patterns are parallel to the impinging radar wave). It is shown that the radar absorbing
properties of the design strongly depend on the electrical conductivity of the paint, the size of
the printed patterns and the orientation of the printed patterns with respect to the impinging
wave. It is shown that a planar FSS has a maximum absorption of 50%, while foldcores and
honeycombs may obtain a higher absorption due to the fact that the patterns are orientated
under an angle with respect to the propagation direction of the wave.

Automated Manufacture of Grid Stiffened Panels

Scipedia content — Thu, 04 Mar 2021 08:58:58 +0100

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.

Comparision of Density Measurement Methods for Unidirectional Flax-Epoxy Polymer Composites

Scipedia content — Thu, 04 Mar 2021 08:56:46 +0100

Density is a decisive factor in determining one of the most important advantages
of flax fiber-reinforced polymer (FFRP) composites, i.e. their relatively low weight leading to
high specific properties. As a fundamental physical property of composites, density enters in
many engineering design and quality control calculations and its value is a determining factor
for several applications. Especially, we need precise material properties including density so
as to develop efficient numerical models to these materials. In this work, three density
measurement methods were evaluated and compared: Helium-gas pycnometry and Archimedes
with two different immersing liquids, water and ethanol. The results show that Helium-gas
pycnometry and Archimedes with ethanol gave similar and repeatable results, whereas using
water resulted in much lower values. The density values were all in the range of reported values.
However, Helium-gas pycnometry or Archimedes using ethanol are recommended for more
precision in measuring the density of FFRP composites.

Contribution of Conformal Antennas Towards Sustainable Aircraft

Scipedia content — Thu, 04 Mar 2021 08:53:24 +0100

This paper shows the drag and emission reduction potential of integrated, flush communication antennas at the surface of an airliner. The CFD simulations of the aircraft model representing a modern airliner with radome in different locations on its upper part of the fuselage have been done. The results have been compared with the baseline configuration of the aircraft without radome. The aerodynamic equivalent weight penalty and additional fuel needed due to the drag of the radome and its weight itself have been calculated by two approaches. The obtained drag reduction potential has been used for the estimation of the CO₂ and NO_x emissions reduction by using integrated antenna.

Cooling of Active Components in Structurally Integrated Phased Arrays Antennas

Scipedia content — Thu, 04 Mar 2021 08:54:27 +0100

This paper presents an innovative cooling solution for active phased array antennas,
using a 3D printed liquid cooling device integrated in the structure’s PCB.

Design Consideration for Fully Embedded Electronically Steerable SatCom Airborne Antenna

Scipedia content — Thu, 04 Mar 2021 08:55:58 +0100

In this paper a conceptual design of a SATCOM On The Move (SOTM) system in
the Ka band is presented. This system is intended to be airborne and fully integrated in an
AIRBUS C295 Flight Test Bench. The system relies in two separated low profile TX and RX
antennas (about half a meter size) which reach up to 10Mbps return link and 50Mbps forward
link.

Development of Multifunctional Materials and Structures with Improved Capacities in Aerodynamics, De-icing, Acoustics or Electromagnetism for Civil and Military Aircrafts

Scipedia content — Thu, 04 Mar 2021 08:59:28 +0100

For several years, either in the frame of research projects (French, European), or for direct
application on aircraft programs, Dassault Aviation has developed multifunctional materials
and structures (MMS) with specific benefits in aerodynamics, de-icing, acoustic or
electromagnetisms. The main challenge is to get the best compromise between the high
functional performances desired and the mechanical and aeronautic environment resistance
needed for the application. This presentation will review some examples of development
performed in the recent years for aircraft aerodynamics improvement, icing protection,
acoustics and new antenna radomes.

Electrical Conductivity and Electromagnetic Shielding Effectiveness of Bio-Composites

Scipedia content — Thu, 04 Mar 2021 08:58:35 +0100

In this paper, electrical conductivity and electromagnetic shielding effectiveness of
two bio-composites have been studied by tests and numerical models. Two monolithic
composites with partly bio-based content were manufactured. The first bio-composite is made
of a carbon fibre fabric prepreg and a partly bio-based (rosin) epoxy resin (CF/Rosin). The
second bio-composite is a combination of prepregs of carbon fibre fabric / epoxy resin and flax
fibre fabric / epoxy resin (CF-Flax/Epoxy). A single line infusion process has been used prior
to the curing step in the autoclave. Both variants are exemplary for the possibility of introducing
bio-based materials in high performance CFRP. In-plane and out-of-plane electrical
conductivity tests have been conducted according to Airbus standards AITM2 0064 and AITM2
0065, respectively. Electromagnetic shielding effectiveness tests have been conducted based on
the standard ASTM D 4935-10. Materials were prepared at the German Aerospace Center
(DLR) while characterization tests were conducted at the University of Patras. In addition to
the tests, numerical models of representative volume elements have been developed using the
DIGIMAT software to predict the electrical conductivity of the two bio-composites. The
preliminary numerical results show a good agreement with the experimental results.

Exploration of Radiating Aerostructures Ultimate Antenna and Structure Integration

Scipedia content — Thu, 04 Mar 2021 08:56:18 +0100

Two antenna designs are described that are both fully integrated into Fiber Metal
Laminate fuselage panels. Full integration in this context means that the antennas are flush with
the fuselage skin on the outside of the aero structure, while maintaining the structural properties
of the FML panel. The antennas are designed to resonate at GNSS and at VHF frequency bands.
Design considerations are discussed and preliminary results are presented.

From Design Towards Manufacturing of Winglets with Integrated VHF Antenna

Scipedia content — Thu, 04 Mar 2021 08:53:50 +0100

This paper shows the technical aspects and the progress of manufacturing a winglet concept with integrated VHF antenna.

Functionalization of Carbon Nanotubes and Mechanical Characterisation of Bio-based Epoxy Nano-composites

Scipedia content — Thu, 04 Mar 2021 08:57:40 +0100

Chemical functionalization of multiwalled carbon nanotubes (MWCNTs) is important from the view
point of polymer based composite manufacturing. As pristine MWCNTs has certain disadvantage such
as they have lower dispersion, they are hydrophobic and are not readily soluble in a solvent, these
characteristics makes them unreliable candidate for most of the industrial applications. By doing
chemical functionalization of MWCNTs, these shortcomings can be overcome, and the MWCNTs can
be used as a filler in composite manufacturing. This has the advantage of better nanofillers’ dispersion
and provide the better interfacial bonding.
In this study, MWCNTs are functionalized by the carboxylic group, chemical functionalization of
MWCNTs is an optimization problem, governed by parameters like mixture acid concentration,
temperature, time of heating and amount of MWCNTs used. Material characterization of MWCNTs is
done and test specimens are manufactured according to different concentrations of MWCNTs within a
bio-based epoxy resin. Mechanical properties are then compared according to different concentrations.
These mechanical and material characterizations increase the understanding of chemical
functionalization by carboxylic group and the influence of the concentration of MWCNTs dispersed
within the bio-based resin matrix.

Integrating Electromagnetic Functions into Fiber Metal Laminates – the Structural Challenge

Scipedia content — Thu, 04 Mar 2021 08:56:32 +0100

This paper outlines aspects, outcome and prospects of full integration of antennas into structural
elements of aircraft, from a structural design perspective.

Manufacturing Aspects of Active Acoustic Lining panel

Scipedia content — Thu, 04 Mar 2021 08:54:12 +0100

This paper shows the technical aspects and the progress of manufacturing a lining
concept with actuators and sensors for noise reduction within the cabin of aircraft with CROR
engine. The structural integration, the repair possibilities and the serial production of such a
lining are focused.

New Enhanced Acoustic Damping Composite Material for the Aeronautics Industry

Scipedia content — Thu, 04 Mar 2021 08:59:16 +0100

The present article investigates an innovative structural composite material concept
with the additional functionality of acoustic damping. It is achieved by introducing an
embedded elastomeric layer within the composite laminate, which constitutes a constrained
layer damping (CLD) system. The main objective is to increase the acoustic performance of
the baseline material, while its mechanical properties are maintained. In addition, material
processability and inspectability have been considered as important drivers for the technology
development. In order to identify the most promising candidate, a set of alternatives has been
explored and analysed, giving rise to a compromise solution between the enhanced acoustic
performance and the structural properties of the baseline material.

Remote Sensing for a Lining Integrated Active Structural Acoustic Control System

Scipedia content — Thu, 04 Mar 2021 08:53:05 +0100

In the framework of the EU project ACASIAS an aircraft sidewall panel (lining) with structurally integrated actuators and sensors is developed. Each lining has a digital unit which samples the sensor signals, performs filtering operations and supplies the actuators with control signals. The whole system makes up an active structural acoustic control system aiming at the reduction of low-frequency multi-tonal aircraft interior noise. The novelty of this approach compared to past implementations of active noise control (ANC) systems in aircraft is its modularity. Each so-called smart lining is autonomous in the sense that it processes only structural sensor data from its own integrated sensors. The use of external microphones for error sensing is avoided because this conflicts with the modularity of the smart lining. Hence, one important design task is the replacement of the physical error microphones by the integrated structural sensors and an acoustic filter (observer) running on the digital unit. This method, which is called the remote microphone technique for active control, has never been applied to an aircraft interior structure so far. The detailed design of the smart lining module comprises several steps which are taken within work package 3 of the ACASIAS project. Experimental data of an aircraft typical double panel system is captured in a sound transmission loss facility. The system is excited with a loudspeaker array placed directly in front of the fuselage structure. Different acoustic load cases are used for the definition of the sensors and the actuators. A multi-tonal excitation with high sound pressure level is relevant for the actuator dimensioning and a broadband excitation with multiple independent sound sources is relevant for the sensor definition. 19 accelerometers are mounted on the lining and 20 microphones are placed in front of it. All sensor signals are sampled simultaneously for deterministic and broadband load cases. The lining is equipped with two inertial mass actuators which are used for the active control. Measured frequency response functions of actuators at 39 positions are used for the optimization of the actuator locations. The measurement data is also used for the derivation of an observer and for the simulation of a smart lining with remote microphones. In this contribution, the steps undertaken for the detailed design will be described and simulation results of the noise reduction performance of the smart lining with remote microphones will be presented.

Structural Analyses of Orthogrid Fuselage Panel for Integrated Ku-band SatCom Antenna.

Scipedia content — Thu, 04 Mar 2021 08:58:09 +0100

The aim of this work is to describe the structural analysis of a multifunctional aircraft
fuselage panel. The structure of the panel has an embedded antenna tiles. The panel consists
of UniDirectional (UD) carbon fibre reinforced composite skin stiffened with ortho-grid ribs,
and a transparent skin window made using UD glass fibre reinforced composite. The orthogrid structure is a structural reinforcement but also the antenna tiles support. The presented
work proposes a numerical multiscale strategy. The laminate is simulated with solid elements,
in order to capture the real kinematics of the material, but several laminas are condensed in
a single finite element. The performance of each lamina is obtained using the Serial-Parallel
(SP) mixing theory. The specific formulations developed have been very useful to identify and
study the mechanical performance of these new structures and the localization of unknown and
un-predicted hot-spots in the structure.

Structural Integration of a Ku-band SatCom Antenna into Novel Fuselage Panel

Scipedia content — Thu, 04 Mar 2021 08:55:41 +0100

This paper addresses the structural integration of a Ku-band SATCOM antenna in
the fuselage of an aircraft. The phased array antenna consists of 25 antenna tiles that are
integrated in an orthogrid fuselage panel. The specific electromagnetic aspects of the antenna integration will be discussed in this paper; this concerns the lightning protection of the antenna tiles and the electromagnetic interaction of the CFRP orthogrid and GFRP fuselage skin with the array antenna. The structural properties and thermal management of the antenna will be discussed in separate papers [1,2,3].

Textile-Integrated Transmitting Unit

Scipedia content — Thu, 04 Mar 2021 08:54:44 +0100

This contribution deals with the main parts of the textile-integrated transmitting
unit, a transmitter and an antenna, operating in the ISM 5.8 GHz band. The transmitter is
based on commercially available WLAN UART Serial Port OWS451 and it is controlled via
the UART interface by microprocessor ATmega328. The antenna is based on the circular
ring-slot concept and it is able to provide monopolar radiation pattern to ensure maximum
coverage of the unit. The unit will be integrated in a seat cover and it will transmit the
telemetry of sensors integrated in the seat (temperature, pressure…).

The ECO-COMPASS EU-China Project

Scipedia content — Thu, 04 Mar 2021 08:59:40 +0100

Fibre reinforced polymers are important materials used in aviation due to their
excellent specific properties enabling the reduction of fuel consumption. For example, carbon
fibre reinforced epoxy resins are used in fuselage and wing structures. Glass fibre reinforced
phenolic resins are mainly used for the interior panels due to their low weight and favourable
fire properties. All these composite materials used in aviation have one thing in common: they
are man-made. Renewable materials like bio-fibres and bio-resins are under investigation for
a long time for composites but they did not made it into modern aircraft in high amounts yet.
The project ECO-COMPASS under Horizon 2020 aims to bundle the knowledge of 17
partners from China and Europe to develop ecological improved composites for the use in
aircraft interior and secondary structures [1]. Bio-based reinforcements, epoxy resin and
sandwich cores are developed and improved for their application in aviation. Furthermore the
use of recycled carbon fibres to increase the mechanical strength and multifunctional aspects
of bio-composites are evaluated. In order to withstand the special stresses in aviation
environment, protection technologies to mitigate the risks of fire, lightning and moisture
uptake are under investigation. An adapted modelling and simulation will enable the
optimization of the composite design. Electrical conductive composites for electromagnetic
interference shielding and lightning strike protection are under investigation in ECOCOMPASS as well. The cooperation includes the exchange of knowledge and materials in
order to optimize the development of ecological friendly composites.

Towards a Lining Integrated Active Structural Acoustic Control System

Scipedia content — Thu, 04 Mar 2021 08:52:06 +0100

For future aircraft counter-rotating open rotor (CROR) engines are a promising technology to reduce their CO₂ footprint. Since the contribution of CROR engines to the cabin noise is higher than for jet engines, new strategies for the reduction of noise transmissions for frequency bands below 500 Hz are necessary. Active structural acoustic control (ASAC) systems are capable to reduce sound transmission of lining structures in this bandwidth. Sensors measure the vibrations of the lining to estimate its sound emission into the cabin. Based on these signals a controller calculates force signals for actuators on the lining. The actuator forces change the vibration behaviour of the lining in order to reduce its sound emission. For the realization of such a system in a real aircraft, manufacturing and maintenance issues have to be addressed. Within work package 3 of the EU project ACASIAS an aircraft lining with an integrated ASAC system is developed. The size of the lining is app. 1300 x 1690 mm² (W x H) and it is simply curved. The radius of 2980 mm makes it relevant for a twin-aisle aircraft like the Airbus A350. The focus of research activities lies on the integration of components and the industrial manufacturing process of the lining. The components to be integrated are sensors, actuators and the corresponding wiring. A concept is proposed where each actuator and sensor is encapsulated in a kind of insert. The inserts smoothly integrate into the manufacturing process of the lining while they protect the actuators and sensors from humidity, dust, etc. The maintenance aspect is covered by the option to change each actuator or sensor upon insert level. The integrated wiring of the lining is left unaffected during an actuator or sensor replacement since connectors in each insert allow a nearly tool-free assembly/disassembly. In this paper the progress of work package 3 is presented at a detailed design review (DDR) stage. Finally, the lining will be manufactured and equipped with a full ASAC system. Experiments will be conducted in the acoustic transmission loss facility at the DLR.