CTM Boom Deployment Mechanism with Integrated Boom Root Deployment for Increased Stiffness of the Boom-to-Spacecraft Interface

CTMs (Collapsible Tube Masts) are well known for small and medium sized solar sails as they can create huge and stiff sail backbone structures out of a very small mass. But one key issue with those masts is the need for a full deployment of the booms cross section in order to generate the full stiffness. Close to the deployment mechanism the stiffness is significantly decreased. Usual mechanisms try to counteract this drawback by guiding rollers or surfaces that support the boom in this weak transition zone. The underlying paper will present a different approach: The boom spool of the novel deployment mechanism contains a simple but reliable mechanism that is triggered at the end of the longitudinal deployment. This inner mechanism deploys the booms cross section and locks the boom spool into the outer walls of the surrounding structure. The result is a boom deployment mechanism that supports the utilization of the full potential of the CTMs

Virtual testing for design and certification of (fusion) bonded longitudinal joints in a fibre composite fuselage: A proposal using FEM-based progressive damage analysis

In the design of bonded aircraft structures, the type of failure is crucial. More specifically, the failure in case of overload should be limited to the surrounding fibre composite structure. Due to the interaction of damage phenomena, failure behaviour cannot be easily predicted. To simplify the design process, guidelines should ensure that the desired failure behaviour occurs. This work investigates if suitable progressive damage analysis methods can, at least in parts, replace physical test campaigns to substantiate these design guidelines. Using the design of a longitudinal fuselage joint as an example, a continuum damage model for composite materials previously developed by the author is used to analyse the strength and occurring failure modes in detail. It is shown that physical tests could be reduced to a minimum in the future

Virtuelles Testen für Design und Zertifizierung von geklebten Längsnähten in FVK-Flugzeugrümpfen

Bei der Auslegung von geklebten Flugzeugstrukturen aus Faserverbundwerkstoffen ist neben der erzielten Festigkeit die Art des Versagens entscheidend. Insbesondere sollte das Versagen im Falle einer Überlast auf die umgebende Faserverbundstruktur beschränkt bleiben. Allerdings lässt sich das Versagensverhalten aufgrund unterschiedlicher möglicher Schadensphänomene und deren Wechselwirkung nicht ohne Weiteres vorhersagen. Um den Entwurfsprozess zu vereinfachen und zu beschleunigen, sollen Konstruktionsrichtlinien daher sicherstellen, dass das gewünschte Versagensverhalten eintritt. In der Forschungsarbeit im Rahmen einer Promotion wurde untersucht, ob geeignete Methoden der numerischen progressiven Schädigungsanalyse physikalische Versuchskampagnen zur Absicherung dieser Auslegungsrichtlinien zumindest teilweise ersetzen können. Am Beispiel der Auslegung einer geklebten Flugzeugrumpflängsnaht wird unter anderem ein vom Autor zuvor entwickeltes Kontinuumsschädigungsmodell für Faserverbundwerkstoffe verwendet, um die Festigkeit und die auftretenden Versagensmodi mit dem kommerziellen FEM-Löser Abaqus/Explicit im Detail zu analysieren. Es wird aufgezeigt, dass physikalische Tests in Zukunft auf ein Minimum reduziert werden könnten

Improving the fatigue life of printed structures using stochastic variations

Additive manufacturing allows designers to create geometries that would not be possible or economical to manufacture using traditional manufacturing processes. Production with these technologies does, however, introduce a large amount of variation and additional unknowns. These random variations from idealized geometry or material properties can harm the performance of the design. The current work presents an approach to improve the fatigue life of such structures, and simultaneously reduce its influence from random variations in local thickness. Following an initial numerical study, the results are experimentally validated. Experimental results show a significant improvement in fatigue life in the redesigned sample with a tailored thickness distribution

Design of a Herringbone-Grooved Bearing for Application in an Electrically Driven Air Compressor

A turbo compressor was investigated to ensure the operational reliability of the charging of fuel cell systems. This study investigated air-lubricated herringbone bearings to support the high-speed rotating shaft. For reliable operation of the rotor bearing system, stable operation in the whole speed range (up to 120 krpm), as well as low lift-off speed, is an important issue. Some publications containing guidelines for an optimized design in terms of stability and lift-off behavior date back to the 1970s, with some simplifying assumptions (such as narrow groove theory and small eccentricity analysis). Many publications have addressed the calculations, as well as the optimization of herringbone-grooved bearings; however, general design guidelines are still missing in the view of the authors. Although the investigations related to bearings for the support of a lightweight rotor for a special compressor of a fuel cell unit, this study could also indicate favorable bearing designs for other high-speed applications. Here, the compressible Reynolds equation was solved in the whole solution domain using a conservative finite difference scheme, and the corresponding bearing characteristics were determined. In a perturbation analysis, the linearized dynamic coefficients of the herringbone bearing are calculated. To compare the suitability and performance of the various herringbone-grooved bearing designs, especially at high speed, the simple model of a Jeffcott rotor airborne with two identical herringbone-grooved journal bearings (HGJBs) was used. The geometrical parameters of the HGJBs were varied, and their effects on bearing characteristics and stability were evaluated. Recommendations concerning favorable geometrical bearing parameters for a sufficiently high stability threshold speed and reasonable low lift-off speed were the result of the parameter study

Structural and Electric Properties of Epitaxial Na0.5Bi0.5TiO3-Based Thin Films

Substantial efforts are dedicated worldwide to use lead-free materials for environmentally friendly processes in electrocaloric cooling. Whereas investigations on bulk materials showed that Na0.5Bi0.5TiO3 (NBT)-based compounds might be suitable for such applications, our aim is to clarify the feasibility of epitaxial NBT-based thin films for more detailed investigations on the correlation between the composition, microstructure, and functional properties. Therefore, NBT-based thin films were grown by pulsed laser deposition on different single crystalline substrates using a thin epitaxial La0.5Sr0.5CoO3 layer as the bottom electrode for subsequent electric measurements. Structural characterization revealed an undisturbed epitaxial growth of NBT on lattice-matching substrates with a columnar microstructure, but high roughness and increasing grain size with larger film thickness. Dielectric measurements indicate a shift of the phase transition to lower temperatures compared to bulk samples as well as a reduced permittivity and increased losses at higher temperatures. Whereas polarization loops taken at −100 °C revealed a distinct ferroelectric behavior, room temperature data showed a significant resistive contribution in these measurements. Leakage current studies confirmed a non-negligible conductivity between the electrodes, thus preventing an indirect characterization of the electrocaloric properties of these films

Transient Dynamic System Behavior of Pressure Actuated Cellular Structures in a Morphing Wing

High aspect ratio aircraft have a significantly reduced induced drag, but have only limited installation space for control surfaces near the wingtip. This paper describes a multidisciplinary design methodology for a morphing aileron that is based on pressure-actuated cellular structures (PACS). The focus of this work is on the transient dynamic system behavior of the multi-functional aileron. Decisive design aspects are the actuation speed, the resistance against external loads, and constraints preparing for a future wind tunnel test. The structural stiffness under varying aerodynamic loads is examined while using a reduced-order truss model and a high-fidelity finite element analysis. The simulations of the internal flow investigate the transient pressurization process that limits the dynamic actuator response. The authors present a reduced-order model based on the Pseudo Bond Graph methodology enabling time-efficient flow simulation and compare the results to computational fluid dynamic simulations. The findings of this work demonstrate high structural resistance against external forces and the feasibility of high actuation speeds over the entire operating envelope. Future research will incorporate the fluid–structure interaction and the assessment of load alleviation capability