A traditional aircraft is optimized for only one or two flight conditions, not for the entire flight envelope. In contrast, the wings of a bird can be reshaped to provide optimal performance at all...

Morphing aircraft based on smart materials and structures: A state-of-the-art review:

The twenty-first century could be called the 'Multifunctional Materials Age' The inspiration for multifunctional materials comes from nature, and therefore these are often referred to as bio-inspired materials Bio-inspired materials encompass smart materials and structures, multifunctional materials and nano-structured materials This is a dawn of revolutionary materials that may provide a 'quantum jump' in performance and multi-capability This book focuses on smart materials, structures and systems, which are also referred to as intelligent, adaptive, active, sensory and metamorphic The purpose of these materials from the perspective of smart systems is their ability to minimize life-cycle cost and/or expand the performance envelope The ultimate goal is to develop biologically inspired multifunctional materials with the capability to adapt their structural characteristics (such as stiffness, damping and viscosity) as required, monitor their health condition, perform self-diagnosis and self-repair, morph their shape and undergo significant controlled motion over a wide range of operating conditions

/pdf/smart-structures-theory-42oodmh8rk.pdf

Smart Structures Theory

Conventional ultrasound inspection has been a standard non-destructive testing method for a long time. In most cases, though, a liquid coupling medium, such as water or gel, is required because of the huge impedance mismatch at a solid-air boundary. The physical contact with a liquid medium is a drawback because it prevents ultrasound inspection of many important materials. Modern industry, however, has a growing need for new, improved and remote non-destructive testing techniques for the inspection of new kinds of materials. 
This thesis describes the use, advantages, limitations, and applications of a commercially available remote air-coupled ultrasound testing system that has been implemented in an accredited non-destructive testing laboratory (EN ISO/IEC 17025: 2000). One of the objectives of the study, therefore, is to discover whether air-coupled ultrasound conforms to standards of modern quality assurance by comparing requirements of modern standards with the possibilities of this new advanced technique. The results are also compared with other non-destructive methods to discover if air-coupled ultrasound testing can compete with current techniques. First, the possibilities of linear air-coupled ultrasound inspection in through-transmission mode are investigated. In this case the equipment is used in its standard mode and ultrasound images (A-, B-, C-scan images) are performed. Second, the measuring technique is further developed to operate in the non-linear mode. This latter method uses the non-linear behaviour of defects for fast and selective imaging. Therefore, the excitation of a sample by injection of a sinusoidal wave using external or internal sources produces higher harmonics at the damaged area. By using these harmonics, defect-selective imaging is performed in which only the defect itself appears. In the case of non-linear air-coupled ultrasound, the sample is excited at frequencies that have the centre frequency of the air-coupled narrow band receiver as an overtone. When the receiver scans across the sample, it responds selectively to the higher harmonics.
In this study, high performance materials, components, and processes that are close to actual applications and that are difficult or impossible to measure with water are inspected. Results of air-coupled ultrasound imaging performed on fibre-reinforced plastics, water sensitive materials (e.g. C/C-SiC ceramic or wood), and smart structures are presented in order to reveal delaminations, impacts, and growth of internal defects. Further measurements of monitoring the curing process of epoxy resin and of the manufacturing process of the new high temperature resistant C/C-SiC ceramic are presented. In addition, results are shown in which the actuator in shape-adaptive structures is used as transmitter and the receiver of the air-coupled system is used to record the signals. Thus it is possible to detect defect areas of the piezo actuators. 
Analysing the results and by comparing them with other non-destructive testing methods demonstrates that air-coupled ultrasound inspection is a promising new technique that is suitable for modern quality assurance and one that can compete with other non-destructive testing methods. 
Herkommliche Ultraschalluntersuchung ist seit langer Zeit eine Standardmethode der zerstorungsfreien Prufung. In den meisten Fallen wird aufgrund des grosen Impedanzunterschiedes an einer Festkorper/Luft Grenzschicht ein flussiges Koppelmedium (beispielsweise Wasser oder Koppelgel) benotigt. Dieser direkte Kontakt ist jedoch ein Nachteil, da er Ultraschallmessungen an vielen wichtigen Materialien unmoglich macht. Zur Untersuchung neuartiger Werkstoffe hat die heutige Industrie jedoch ein wachsendes Bedurfnis fur neue, weiterentwickelte und beruhrungslose zerstorungsfreie Prufverfahren. 
Diese Arbeit beschreibt den Einsatz, die Vorteile, die Grenzen und die Anwendungen eines kommerziell erhaltlichen luftgekoppelten Ultraschallsystems, welches in ein akkreditiertes Pruflabor (EN ISO/IEC 17025: 2000) eingebunden worden ist. Eine der Zielsetzungen dieser Arbeit ist deshalb herauszufinden, ob luftgekoppelter Ultraschall die Standards der modernen Qualitatssicherung erfullt. Die geschieht durch den Vergleich der Forderungen heutiger Standards mit den Moglichkeiten dieser neuen fortschrittlichen Technik. Die Ergebnisse werden gleichfalls mit weiteren zerstorungsfreien Methoden verglichen, um zu beurteilen, ob luftgekoppelter Ultraschall mit gegenwartigen Verfahren konkurrieren kann. Zuerst werden die Moglichkeiten des linearen luftgekoppelten Ultraschalls in Transmissionskonfiguration untersucht. Dabei wird die Messeinrichtung in ihrem Standardmodus verwendet und Ultraschallbilder (A-, B-, C-Bilder) aufgezeichnet. Dann wird die Messtechnik weiterentwickelt, um sie im nichtlinearen Modus zu betreiben. Diese letztere Methode verwendet das nichtlineare Verhalten von Fehlstellen fur eine schnelle und selektive Darstellung von Defekten. Eine sinusformige Anregung (externe oder interne Anregungsquelle) erzeugt hohere Harmonische in den geschadigten Bereichen. Die Verwendung dieser Harmonischen ermoglicht eine defekt-selektive Darstellung, in der nur die Fehlstellen selbst abgebildet werden. Im Fall des nichtlinearen luftgekoppelten Ultraschalls wird die Probe mit Frequenzen angeregt, die die Mittelfrequenz eines luftgekoppelten schmalbandigen Empfangsprufkopfs als Oberton haben. Beim Abrastern der Probe reagiert der Prufkopf selektiv auf die hoheren Harmonischen. 
In dieser Arbeit werden Hochleistungswerkstoffe, Bauteile und Prozesse untersucht, die nah an praktischen Anwendungen sind und die schwer oder uberhaupt nicht mit Wasser untersucht werden konnen. Es werden Ergebnisse von luftgekoppelten Ultraschall prasentiert, die an faserverstarkten Kunststoffen, wasserempfindlichen Werkstoffen (beispielsweise C/C-SiC Keramik oder Holz) und an formadaptiven Strukturen durchgefuhrt wurden, um Delaminationen, Impactschaden und das Wachstum innerer Fehlstellen zu erfassen. Daruber hinaus werden Messungen dargestellt, bei denen der Aushartevorgang von Epoxidharz und der Produktionsprozess der neuen hochtemperaturbestandigen C/C-SiC Keramik uberwacht wird. Weiterhin werden Ergebnisse gezeigt, bei denen der Aktor einer adaptiven Struktur als Sender verwendet wird und die Signale mit dem Empfanger der Luftultraschallanlage aufzeichnet werden. Auf diese Weise ist es moglich, fehlerhafte Bereiche eines Piezoaktors zu finden.
Durch die Betrachtung der Ergebnisse und deren Vergleich mit weiteren zerstorungsfreien Testmethoden wird gezeigt, dass luftgekoppelter Ultraschall eine vielversprechende neue Technik ist, die fur moderne Qualitatssicherung geeignet ist und die mit anderen zerstorungsfreien Methoden konkurrieren kann.

Air-coupled ultrasound inspection as a new non-destructive testing tool for quality assurance

This paper is about recent advances in Eurocopter’s research activities on passive and active vibration control systems. Emphasis is placed on the reduction of rotor-induced vibrations which is still one of the key challenges in helicopter dynamics. Both passive and active means for the reduction of vibrations are discussed. A short review of the rotor-induced vibration problem is given with a link to typical vibration characteristics of Eurocopter helicopters. The concepts and means to influence and control vibrations are outlined. The main focus of this paper is on recent advances on i) vibration control at the rotor, ii) vibration control at the transmission and iii) vibration control at the fuselage. In the section “vibration control at the rotor”, vibrations are attacked at their source – the rotor itself. Advanced passive and active rotor dynamic layouts are of interest. Here, a 5-bladed bearingless vs. 4bladed main rotor system on EC145 as well as an active flap rotor on the hingeless system of BK117 are discussed. For each system, key parameters of the design, data of the test configuration and test environment and in particular results on vibration reduction are presented. A substantial reduction of the exciting hub loads is achieved thus providing superior airframe vibration levels. In the section “vibration control at the transmission”, a new generation of pylon isolation system is presented. This passive system based on the SARIB principle combines advantages of efficiency, lightness, reliability and low cost design. This technology consists of a compact suspension and a flapping mass integrated in each gear box strut. It provides an important attenuation of the vibrations for all hub loads components and it was successfully tested in-flight. In the section “vibration control at the fuselage”, active anti-vibration control systems (AVCS) installed in the fuselage are presented. The systems rely on single-port active devices which are capable to generate inertia-based control forces which induce a secondary vibration field to compensate the vibration disturbance. Here, systems based on electromagnetic actuation technology for EC225 as well as Piezo-ceramic technology demonstrated on EC135 are presented.

Recent advances in Eurocopter's passive and active vibration control

Since the early helicopter developments, these aircraft have made a tremendous progress in performance, handling qualities, comfort and efficiency. However, modern helicopters still suffer from many problems that hinder a further increase in their efficiency, acceptance and hence their market share. The high level of vibrations and the noise generated by the rotor are the most important reasons for this. While vibrations are a concern of pilot and passenger comfort, they also give rise to an increase in maintenance efforts and costs. The high noise level limits the acceptance of helicopters in the public, e.g. landing of helicopters on or close to hospitals during EMS missions. High noise levels also lead to an early aural detection during military missions. Further drawbacks of helicopters are the high fuel consumption in high speed forward flight due to the excessive power required, the limited speed of flight, the low range for the same reason, low lead-lag damping, etc. To alleviate these drawbacks of helicopters, active rotor control technologies have been investigated for a long time. Many different approaches have been investigated and most of them are not being followed any more. First investigations started with so-called Higher Harmonic Control (HHC) which has been replaced by Individual Blade Control (IBC). The paper gives a survey of the typical problems and explains the vibration and noise issues in more detail. Since active means have to compete with passive ones, such methods are also briefly addressed. Next, the paper gives a review on important HHC achievements. Due to space constraints, the paper mainly focuses on wind tunnel and flight test results. A second paper reviews IBC and gives an outlook on the idea of the swashplateless helicopter.

Eurocopter Deutschland

Papers

Recent advances in Eurocopter's passive and active vibration control

Active Blade Flaps - The Needs and Current Capabilities