Special Issue "Adaptive/Smart Structures and Multifunctional Materials with Application to Morphing Aircraft"

A special issue of Aerospace (ISSN 2226-4310).

Deadline for manuscript submissions: closed (31 May 2015).

Special Issue Editor

Dr. Rafic Ajaj
Website
Guest Editor
Department of Aerospace Engineering, Khalifa University, Abu Dhabi, UAE
Interests: morphing aircraft; aircraft design; adaptive/smart structures; aircraft structures; UAVs; acoustic fatigue
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Special Issue Information

Dear Colleagues,

Recent advances in smart structures and multifunctional materials have facilitated many novel aerospace technologies such as morphing aircraft. A morphing aircraft, bio-inspired by natural fliers, has gained a lot of interest as a potential technology to meet the ambitious goals of the Advisory Council for Aeronautics Research in Europe (ACARE) Vision 2020 and the FlightPath 2050 documents. A morphing aircraft continuously adjusts its wing geometry to enhance flight performance, control authority, and multi-mission capability.

In the last 30 years, there have been a number of international research programmes and projects on morphing wings. Many of these programmes are still active, especially in Europe. These programmes/projects have developed many adaptive/smart structures to allow large and small shape changes and they have investigated multifunctional materials to act as actuators and/or sensors. Furthermore, adaptive structures and multifunctional materials have been used to design compliant skins which are one of the main challenges of morphing wings. These skins have to be flexible in the morphing direction but rigid in other directions to maintain the aerodynamic shape of the wing and withstand the aerodynamic loads. The other main challenge facing morphing aircraft is the ability to design light weight, stiff, and robust adaptive structures that require minimal actuation power.

The use of adaptive/smart structures and multifunctional materials is not limited to morphing aircraft but has been used extensively in other fields, such as structural health monitoring, energy harvesting, suspension systems, wind-turbine blades, race cars, and many others. Therefore, we invite papers either addressing the research opportunities outlined here, or in the general topic area of adaptive/smart structures and multifunctional materials that will make a substantive contribution to the state of the art.

Dr. Rafic Ajaj
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Aerospace is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.


Keywords

  • adaptive structures
  • multifunctional materials
  • morphing aircraft
  • actuators
  • sensors
  • energy harvesting
  • structural health monitoring
  • suspension systems
  • wind-turbine blades
  • compliant skins

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Published Papers (5 papers)

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Editorial

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Open AccessEditorial
Special Issue: Adaptive/Smart Structures and Multifunctional Materials with Application to Morphing Aircraft
Aerospace 2014, 1(3), 98-99; https://doi.org/10.3390/aerospace1030098 - 16 Dec 2014
Abstract
Recent advances in smart structures and multifunctional materials have facilitated many novel aerospace technologies such as morphing aircraft. A morphing aircraft, bio-inspired by natural fliers, has gained a lot of interest as a potential technology to meet the ambitious goals of the Advisory [...] Read more.
Recent advances in smart structures and multifunctional materials have facilitated many novel aerospace technologies such as morphing aircraft. A morphing aircraft, bio-inspired by natural fliers, has gained a lot of interest as a potential technology to meet the ambitious goals of the Advisory Council for Aeronautics Research in Europe (ACARE) Vision 2020 and the FlightPath 2050 documents. A morphing aircraft continuously adjusts its wing geometry to enhance flight performance, control authority, and multi-mission capability.[...] Full article

Research

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Open AccessArticle
Optimization of Variable Stiffness Laminates and Sandwiches Undergoing Impulsive Dynamic Loading
Aerospace 2015, 2(4), 602-626; https://doi.org/10.3390/aerospace2040602 - 23 Oct 2015
Cited by 1
Abstract
This paper, which deals with variable stiffness composites, is aimed at showing the effects of optimization on the response characteristics and stress fields of these materials. A new optimization technique that has recently been developed is used to find spatially variable distributions of [...] Read more.
This paper, which deals with variable stiffness composites, is aimed at showing the effects of optimization on the response characteristics and stress fields of these materials. A new optimization technique that has recently been developed is used to find spatially variable distributions of stiffness properties at any point, which minimize the interlaminar stresses without significant stiffness loss. After solving the Euler–Lagrange equations obtained by the strain energy extremization with varying the stiffness properties, curvilinear paths of fibres are found in closed form that modify natural frequencies, improve dynamic response and aid in recovery of critical interlaminar stresses. In the current version of the optimization technique, a more realistic description of the optimized shear coefficients is provided in order to accurately describe local effects. As a structural model, a zig-zag model with variable through-the-thickness kinematics is adopted, which is able to adapt itself to variations in solutions, thus providing accurate results from constitutive equations. This model is adopted because an accurate description of strain energy is mandatory for an effective application of the optimization procedure proposed. The numerical results show that the optimization procedure effectively recovers the stress concentrations while simultaneously improving the dynamic response of laminates and sandwiches. Full article
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Open AccessArticle
Performance Comparison between Optimised Camber and Span for a Morphing Wing
Aerospace 2015, 2(3), 524-554; https://doi.org/10.3390/aerospace2030524 - 08 Sep 2015
Cited by 9
Abstract
Morphing technology offers a strategy to modify the wing geometry, and the wing planform and cross-sectional parameters can be optimised to the flight conditions. This paper presents an investigation into the effect of span and camber morphing on the mission performance of a [...] Read more.
Morphing technology offers a strategy to modify the wing geometry, and the wing planform and cross-sectional parameters can be optimised to the flight conditions. This paper presents an investigation into the effect of span and camber morphing on the mission performance of a 25-kg UAV, with a straight, rectangular, unswept wing. The wing is optimised over two velocities for various fixed wing and morphing wing strategies, where the objective is to maximise aerodynamic efficiency or range. The investigation analyses the effect of the low and high speed velocity selected, the weighting of the low and high velocity on the computation of the mission parameter, the maximum allowable span retraction and the weight penalty on the mission performance. Models that represent the adaptive aspect ratio (AdAR) span morphing concept and the fish bone active camber (FishBAC) camber morphing concept are used to investigate the effect on the wing parameters. The results indicate that generally morphing for both span and camber, the aerodynamic efficiency is maximised for a 30%–70% to 40%–60% weighting between the low and high speed flight conditions, respectively. The span morphing strategy with optimised fixed camber at the root can deliver up to 25% improvement in the aerodynamic efficiency over a fixed camber and span, for an allowable 50% retraction with a velocity range of 50–115 kph. Reducing the allowable retraction to 25% reduces the improvement to 8%–10% for a 50%–50% mission weighting. Camber morphing offers a maximum of 4.5% improvement approximately for a velocity range of 50–90 kph. Improvements in the efficiency achieved through camber morphing are more sensitive to the velocity range in the mission, generally decreasing rapidly by reducing or increasing the velocity range, where span morphing appears more robust for an increase in velocity range beyond the optimum. However, where span morphing requires considerable modification to the planform, the camber change required for optimum performance is only a 5% trailing edge tip deflection relative to cross-sectional chord length. Span morphing, at the optimal mission velocity range, with 25% allowable retraction, can allow up to a 12% increase in mass before no performance advantage is observed, where the camber morphing only allows up to 3%. This provides the designer with a mass budget that must be achieved for morphing to be viable to increase the mission performance. Full article
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Open AccessArticle
Decamber Morphing Concepts by Using a Hybrid Trailing Edge Control Surface
Aerospace 2015, 2(3), 482-504; https://doi.org/10.3390/aerospace2030482 - 28 Jul 2015
Cited by 4
Abstract
The idea of morphing is drawing extensive attention in aerospace technologies. Several different approaches like span, camber, twist, and sweep are finding applications. In this work, the concept of a trailing edge control surface which is capable of performing decamber morphing is explained. [...] Read more.
The idea of morphing is drawing extensive attention in aerospace technologies. Several different approaches like span, camber, twist, and sweep are finding applications. In this work, the concept of a trailing edge control surface which is capable of performing decamber morphing is explained. The upper and lower parts of the control surface undergo different chordwise elongations and the difference between these displacements gives rise to either camber or decamber morphing. The necessary force is achieved by the help of servo actuators. During the design, the structural analyses were done to determine the best viable options for the number of servo actuators, the location of the servo actuators, and the material properties used in the control surface. The control surface was designed of aluminum, composite and compliant materials hence was called a hybrid one. The structural analyses were conducted by using ANSYS® Workbench v14.0 package program. After finding the best viable design, which was made for in vacuo condition, the proposed design was also verified under the simulated aerodynamic loading. The aerodynamic loads were obtained from CFD analyses which were done with SU2 V3.2.3 open-source flow solver. Full article
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Open AccessArticle
Graphene/Epoxy Coating as Multifunctional Material for Aircraft Structures
Aerospace 2015, 2(3), 423-434; https://doi.org/10.3390/aerospace2030423 - 30 Jun 2015
Cited by 36
Abstract
Recently, the use of graphene as a conductive nanofiller in the preparation of inorganic/polymer nanocomposites has attracted increasing interest in the aerospace field. The reason for this is the possibility of overcoming problems strictly connected to the aircraft structures, such as electrical conductivity [...] Read more.
Recently, the use of graphene as a conductive nanofiller in the preparation of inorganic/polymer nanocomposites has attracted increasing interest in the aerospace field. The reason for this is the possibility of overcoming problems strictly connected to the aircraft structures, such as electrical conductivity and thus lightning strike protection. In addition, graphene is an ideal candidate to enhance the anti-corrosion properties of the resin, since it absorbs most of the light and provides hydrophobicity for repelling water. An important aspect of these multifunctional materials is that all these improvements can be realized even at very low filler loadings in the polymer matrix. In this work, graphene nanoflakes were incorporated into a water-based epoxy resin, and then the hybrid coating was applied to Al 2024-T3 samples. The addition of graphene considerably improved some physical properties of the hybrid coating as demonstrated by Electrochemical Impedance Spectroscopy (EIS) analysis, ameliorating anti-corrosion performances of raw material. DSC measurements and Cross-cut Test showed that graphene did not affect the curing process or the adhesion properties. Moreover, an increment of water contact angle was displayed. Full article
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