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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Passive biomimetic actuators : the role of material architecture

Guiducci, Lorenzo January 2013 (has links)
Passive plant actuators have fascinated many researchers in the field of botany and structural biology since at least one century. Up to date, the most investigated tissue types in plant and artificial passive actuators are fibre-reinforced composites (and multilayered assemblies thereof) where stiff, almost inextensible cellulose microfibrils direct the otherwise isotropic swelling of a matrix. In addition, Nature provides examples of actuating systems based on lignified, low-swelling, cellular solids enclosing a high-swelling cellulosic phase. This is the case of the Delosperma nakurense seed capsule, in which a specialized tissue promotes the reversible opening of the capsule upon wetting. This tissue has a diamond-shaped honeycomb microstructure characterized by high geometrical anisotropy: when the cellulosic phase swells inside this constraining structure, the tissue deforms up to four times in one principal direction while maintaining its original dimension in the other. Inspired by the example of the Delosoperma nakurense, in this thesis we analyze the role of architecture of 2D cellular solids as models for natural hygromorphs. To start off, we consider a simple fluid pressure acting in the cells and try to assess the influence of several architectural parameters onto their mechanical actuation. Since internal pressurization is a configurational type of load (that is the load direction is not fixed but it “follows” the structure as it deforms) it will result in the cellular structure acquiring a “spontaneous” shape. This shape is independent of the load but just depends on the architectural characteristics of the cells making up the structure itself. Whereas regular convex tiled cellular solids (such as hexagonal, triangular or square lattices) deform isotropically upon pressurization, we show through finite element simulations that by introducing anisotropic and non-convex, reentrant tiling large expansions can be achieved in each individual cell. The influence of geometrical anisotropy onto the expansion behaviour of a diamond shaped honeycomb is assessed by FEM calculations and a Born lattice approximation. We found that anisotropic expansions (eigenstrains) comparable to those observed in the keels tissue of the Delosoperma nakurense are possible. In particular these depend on the relative contributions of bending and stretching of the beams building up the honeycomb. Moreover, by varying the walls’ Young modulus E and internal pressure p we found that both the eigenstrains and 2D elastic moduli scale with the ratio p/E. Therefore the potential of these pressurized structures as soft actuators is outlined. This approach was extended by considering several 2D cellular solids based on two types of non-convex cells. Each honeycomb is build as a lattice made of only one non-convex cell. Compared to usual honeycombs, these lattices have kinked walls between neighbouring cells which offers a hidden length scale allowing large directed deformations. By comparing the area expansion in all lattices, we were able to show that less convex cells are prone to achieve larger area expansions, but the direction in which the material expands is variable and depends on the local cell’s connectivity. This has repercussions both at the macroscopic (lattice level) and microscopic (cells level) scales. At the macroscopic scale, these non-convex lattices can experience large anisotropic (similarly to the diamond shaped honeycomb) or perfectly isotropic principal expansions, large shearing deformations or a mixed behaviour. Moreover, lattices that at the macroscopic scale expand similarly can show quite different microscopic deformation patterns that include zig-zag motions and radical changes of the initial cell shape. Depending on the lattice architecture, the microscopic deformations of the individual cells can be equal or not, so that they can build up or mutually compensate and hence give rise to the aforementioned variety of macroscopic behaviours. Interestingly, simple geometrical arguments involving the undeformed cell shape and its local connectivity enable to predict the results of the FE simulations. Motivated by the results of the simulations, we also created experimental 3D printed models of such actuating structures. When swollen, the models undergo substantial deformation with deformation patterns qualitatively following those predicted by the simulations. This work highlights how the internal architecture of a swellable cellular solid can lead to complex shape changes which may be useful in the fields of soft robotics or morphing structures. / Passive pflanzliche Aktuatoren sind bewegliche Strukturen, die eine komplexe Bewegung ohne jegliche metabolische Energiequelle erzeugen können. Diese Fähigkeit entstammt dabei der Materialverteilung mit unterschiedlicher Quellbarkeit innerhalb der Gewebsstruktur.Die bis heute am besten untersuchten Gewebearten pflanzlicher und künstlicher Passivaktuatoren sind Faserverbundwerkstoffe, in denen steife, fast undehnbare Zellulosemikrofibrillen die ansonsten isotrope Schwellung einer Matrix leiten. Darüber hinaus gibt es in der Natur Beispiele für Aktuationssysteme, wie z.B. die Delosoperma nakurense Samenkapsel, in der das Aktuatorgewebe eine Wabenstruktur aufweist, deren Zellen mit einem hochquellenden Material gefüllt sind. Dabei hat die Wabenstruktur des Gewebes eine hohe geometrische Anisotropie, so dass sich das Gewebe bei Wasseraufnahme bis zur vierfachen Länge entlang einer Hauptrichtung ausdehnt und somit die reversible Öffnung der Kapsel angetrieben wird. Inspiriert durch das Vorbild der Delosoperma nakurense, wird in der vorliegenden Arbeit die Rolle der Architektur von 2D-Zellulärmaterialien als Modell für natürliche passive Aktuatoren analysiert. Zunächst wird anhand eines einfachen Flüssigkeitsdrucks in den Zellen der Einfluss verschiedener architektonischer Parameter auf deren mechanische Betätigung untersucht. Wohingegen regelmäßige konvexe Wabenstrukturen (wie z. B. sechseckige, dreieckige oder quadratische Gitter) sich unter Druck isotropisch verformen, wird durch Finite-Elemente-Simulationen gezeigt, dass es bei anisotropen und nicht-konvexen Zellen zu großen Ausdehnungen jeder einzelnen Zelle kommt. Auch wenn nur eine einzelne Zellgeometrie betrachtet wird, können hierbei viele verschiedene Gitter entstehen. Die Ausdehnungsrichtung des Gitters ist variabel und hängt von der lokalen Konnektivität der Zellen ab. Dies hat Auswirkungen sowohl auf makroskopischer (Gitter-) als auch auf mikroskopischer (Zell-) Ebene. Auf makroskopischer Ebene erfahren diese nicht-konvexen Gitter entweder große anisotrope (ähnlich der Delosperma nakurense Samenkapsel) oder vollkommen isotrope Eigendehnungen, große Scherverformungen oder jeweilige Mischformen. Überdies können Gitter mit ähnlichem makroskopischem Verhalten gänzlich unterschiedliche mikroskopische Verformungsmuster zeigen, wie z.B. Zick-Zack-Bewegungen oder radikale Änderungen der ursprünglichen Zellform. Dies verursacht auch eine entsprechende Änderung der elastischen Eigenschaften. In Abhängigkeit der Gitterarchitektur kann es zu gleichen oder unterschiedlichen mikroskopischen Zelldeformationen kommen, die sich in Summe entweder verstärken oder ausgleichen, und somit die Vielzahl an makroskopischen Verhalten erklären. Interessanterweise lassen sich mit Hilfe einfacher geometrischer Argumente aus der nichtdeformierten Zellform und Zellkonnektivität die Ergebnisse der FE-Simulationen vorhersagen. Die Ergebnisse der Finite-Elemente-Simulationen wurden durch Laborversuche bestätigt, in denen (mit 3D-Drucktechnik gefertigte) Modellgitter ähnliches Ausdehnungsverhalten beim Quellen zeigen. Diese Arbeit zeigt auf, wie die Innenarchitektur eines quellfähigen zellulären Feststoffs zu komplexen Formänderungen führen kann, die in den Bereichen der Soft-Robotik oder bei Morphing-Strukturen angewandt werden können.
2

Revolverová hlava pro dlouhotočný automat s elektricky ovládaným indexováním / Turret Head for CNC Sliding Headstock Machine with Electrical Control Indexing

Úšela, Tomáš January 2008 (has links)
Imposition of my diploma thesis is replace current fluid motor that the derive benefit from to indexing turret head behind electrically driven motor in the sliding headstock machine with indication KMX 326 C. Suggested system must be the most toughest and have to correspond with all the dated up parameters for cutting. Integral part of structural design is also becomingly select accurate blocking a turret head. Fluid motor substitutes behind electrical drive from next reasons: - high transmission loss on energy - sensitivity to cleanness liquid - characteristics mechanism depend upon features liquid ( thermal expansivity, fadeaway)
3

Aktivizující metody a techniky učení v předmětu chemie na základní škole / Actuating methods and techniques of teaching in the subject of Chemistry at elementary school

BUDKOVÁ, Veronika January 2008 (has links)
The aim of this thesis was to prove effectiveness of suitable teaching techniques and actuating methods into the subject of Chemistry. The endeavour was to increase pupils{\crq} activity, to hold pupils{\crq} interest on taught subject matter by a suitable leading and to achieve better results of knowledge of a chosen group of pupils in the end of the research. Within the experiment, there were chosen two groups of pupils of the 9th class. Every class has been situated at a different school. A class at the Elementary School in Počátky was chosen as the first experimental group. The experimental teaching was complemented with suitable actuating methods and techniques of teaching. A class from the Elementary School in Žďár nad Sázavou was chosen for the checking group. This group was taught by traditional methods. On the basis of evaluation of input and output tests, the results were gained and confirmed the effectiveness of the experimental teaching.
4

Embedded sensing and actuating in CFRP composite structures - concept and technology demonstration for tailored embeddable sensor-actuator layers (TEmSAL)

Hornig, Andreas, Frohberg, Richard, Bätzel, Tim, Gude, Maik, Modler, Niels 21 May 2024 (has links)
Carbon fibre reinforced plastic (CFRP) materials are of interest for the aerospace and aviation industry to master growing economic and ecological challenges. In contrast to conventional metallic materials, they offer both higher specific material properties, such as strengths, stiffnesses, and an increased energy absorption capacity in case of impact loading scenarios. Additionally, the possibility of integrating functional elements, such as actuators and sensors, predestine CFRP for the development of more lightweight structural components. In this study, a generic composite structure is instrumented with embedded piezo ceramic sensor elements. A technology for TEmSAL is presented and applied within an autoclave manufacturing process. Aspects of the designing process, manufacturing and instrumentation as well as experimental impact sensing and self-actuation results are presented and discussed.

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