1,681 Works

Bauteilqualität und Werkzeugverschleiß beim Fräsen von CFK-Gelege unter räumlichen Eingriffsbedingungen

Felix Brügmann
Durch Modellierung der räumlichen Eingriffsbedingungen sowie der Faserüberstände in Abhängigkeit von der Bauteilkontur wurden der Einfluss auf die Schnittqualität beim Fräsen von CFK-Gelege analysiert und optimierte Frässtrategien abgeleitet. Zudem wurde der Einfluss des Faserorientierungswinkels auf den Werkzeugverschleiß beim Fräsen im Vollschnitt nachgewiesen und mittels eines empirischen Modells durch Hobelversuche untersucht.

High-temperature stable Zirconia particles doped with Yttrium, Lanthanum, and Gadolinium

Elisabeth Leib, Robert M. Pasquarelli, Malte Blankenburg, Martin Müller, Andreas Schreyer, Rolf Janßen, Horst Weller & Tobias Vossmeyer
Zirconia microspheres synthesized by a wet-chemical sol–gel process are promising building blocks for various photonic applications considered for heat management and energy systems, including highly effi cient refl ective thermal barrier coatings and absorbers/emitters used in thermophotovoltaic systems. As previously shown, pure zirconia microparticles deteriorate at working temperatures of ≥1000 °C. While the addition of yttrium as a dopant has been shown to improve their phase stability, pronounced grain growth at temperatures of ≥1000 °C...

Reliable data streams in the presence of external interference

Florian Meyer
Vermaschte Netzwerke, als ein Mittel zur drahtlosen Kommunikation in großen industriellen Anwendungen, haben über die letzten Jahre mehr und mehr an Popularität gewonnen. Dabei stellen diese Anwendungen neue Anforderungen an die konventionellen drahtlosen Lösungen bezüglich ihrer Zuverlässigkeit und Voraussagbarkeit unter dem Einfluss externer Störungen, besonders bei der Kontrolle und Überwachen von sicherheitskritischen Systemen. Viele Anwendungen verlangen gar eine vollständig verlustfreie Datenübertragung, in dem Sinne, dass jedes auf der Anwendungsschicht versendete Paket schlussendlich beim Empfänger ankommt....

Process development for the simultaneous microbial production of n-butanol and 1,3-propanediol

Christin Prescher
This thesis comprises the development of a biotechnological process for the simultaneous production of n-butanol and 1,3-propanediol with Clostridium pasteurianum DSMZ 525, growing on substrates from renewable resources. The influence of carbon sources with different reductive states, iron availability in the medium, redox active mediators and electro-bioreactors on metabolism and productivity were analyzed. For the recovery of inhibiting n-butanol, in situ gas stripping was implemented in the fermentation process and further optimized. Under the best...

Joint analysis of TDMA and geographic routing for a large scale wireless mesh network

Tobias Lübkert
Wireless Mesh Networks are a promising technique for large scale networks with low-power and high reliability requirements such as in industrial plants. The shared transmission medium requires a medium access control mechanism which reduces the amount of parallel transmission, because nearby simultaneous transmitting devices hinder the successful reception at the destination device. The common CSMA-CA mechanism cannot satisfy the reliability requirement of an industrial plant, as many messages get dropped when the channel is busy...

Photonic glass for high contrast structural color

Guoliang Shang, Lukas Maiwald, Hagen Renner, Dirk Jalas, Maksym Dosta, Stefan Heinrich, Alexander Petrov & Manfred Eich
Non-iridescent structural colors based on disordered arrangement of monodisperse spherical particles, also called photonic glass, show low color saturation due to gradual transition in the reflectivity spectrum. No significant improvement is usually expected from particles optimization, as Mie resonances are broad for small dielectric particles with moderate refractive index. Moreover, the short range order of a photonic glass alone is also insufficient to cause sharp spectral features. We show here, that the combination of a...

Untersuchung des Einflusses der Struktursteifigkeit auf Eislasten

Maximilian Miotke
Diese Arbeit beschäftigt sich mit Eis-Struktur-Interaktionsversuchen mit Hilfe derer der Einfluss der Struktursteifigkeit auf Eislasten experimentell untersucht wird. Hierbei werden sowohl physikalische (Dicke, Temperatur) als auch mechanische (Druckfestigkeit, Biegesteifigkeit, relative/ absolute Durchbiegung, Reibungsverluste, Reaktionskräfte, Kontaktflächenentwicklung) Aspekte betrachtet. Es werden bisherige Erkenntnisse und Wissen aufgegriffen und zusammen mit den neuen Erkenntnissen Rückschlüsse auf das Eis-Stahl-Verhalten geschlossen.

The measurement of the Young's modulus of ice with ultrasonic waves

Kulbir Singh Randhawa
Many techniques have been used to measure the Young’s modulus of ice. The purpose of this bachelor thesis is to develop a more effective and precise technique. The impulse-echo method has been used to measure the longitudinal ultrasonic velocities of three different types of specimens. From this, the Young’s modulus has been calculated. The specimens included homogeneous, inhomogeneous and a cracked polycrystalline ice Ih sample. The homogenous samples studied were found to be elastic isotropic,...

Entwicklung eines Verfahrens zur Bewertung der Festigkeit von beschädigten Schiffen

Martin Salzwedel

Fatigue crack growth rate measurements in GL D36 grade welded structural steel

Josef Göpfrich
In this master thesis, the differences in the crack growth behavior of welded and base material is investigated. The direct current potential drop method is used to document the crack propagation. The material are tested using middle tension samples. The test is carried out with cyclic loading, a force ratio of 0.1 and a frequenze of approximately 33 Hz. Based on the test result a calibration curve is created using the Johnson formular. With the...

Investigation of constraint effect on fatigue crack growth rate measurements

Veronika Hochfellner
For the purpose of reliable life prediction the fatigue crack growth behaviour of a material has to be well-known. Therefore standardized fatigue crack growth tests are made with test specimens of the material. The obtained fatigue crack growth data is taken as material specific data and is given without any information of the test conditions and used specimen geometry. However, in several studies a geometry dependency of the test specimen on the fatigue crack growth...

Deformation mechanisms in nanoporous metals : effect of ligament shape and disorder

Jingsi Jiao & Norbert Huber
The current work presents a numerical modelling approach for investigating the effect of ligament shape and disorder on the macroscopic mechanical response of nanoporous gold (NPG). The approach starts from a ‘single ligament’ analysis with respect to three fundamental deformation modes, bending, torsion, and compression, that depend on the ligament shape. It can be shown that the predictive capability of the highly computationally efficient beam model is sufficient for a large variation in ligament shapes....

Silver-rich clusters in nanoporous gold

Tobias Krekeler, Anastasia V. Straßer, Matthias Graf, Ke Wang, Christian Hartig, Martin Ritter & Jörg Weißmüller
Herein we report on how to render Ti3C2Tx (MXene) monolayers deposited on SiO2/Si wafers, with different SiO2 thicknesses, visible. Inputting the effective thickness of a Ti3C2Tx monolayer (1 ± 0.2 nm) measured by atomic force microscopy, and its refractive index into a Fresnel-law-based simulation software, we show that the optical contrast of Ti3C2Tx monolayers deposited on SiO2/Si wafers depends on the SiO2 thickness, number of MXene layers, and the light’s wavelength. The highest contrast was found for SiO2...

Die Architektur von Offenheit - Überlegungen zur Gestaltung der digitalen Transformation

Axel Dürkop
Vortragstext der Nachwuchskeynote auf dem Jungen Forum für Medien und Hochschulentwicklung 2017 an der Uni Hamburg. Die Potenziale der Gestaltung von Offenheit sozio-technischer Systeme bilden sich in der Architektur ab. Entscheidungen im Entwicklungsprozess dieser Systeme sind nicht nur gestalterischer, sondern auch politischer Art. Am Ende des Beitrags werden Beispiele für dezentrale und föderierte Architekturen entfaltet.

Ein technisches System für die kollaborative OER-Entwicklung im Experimentierfeld der TUHH

Axel Dürkop, Andreas Böttger, Tina Ladwig & Sönke Knutzen
Der Artikel führt ein in ein umgesetztes Konzept zur kollaborativen Entwicklung von Open Educational Ressources (OER) im Experimentierfeld der HOOU an der TUHH. Dabei werden Erfahrungen sowohl aus dem sozialen und organisatorischen Prozess berichtet als auch informationstechnische Systeme und ihr Zusammenspiel vorgestellt.

Hierarchical microcrack model for materials exemplified at enamel

Hüseyin Özcoban, Ezgi D. Yilmaz & Gerold A. Schneider
This article investigates the mechanical properties of a material with hierarchically arranged microcracks.

Entwicklung einer offenen technischen Infrastruktur für HOOU-Lernarrangements an der TUHH

Axel Dürkop
Der Aufsatz beschreibt eine technische Infrastruktur für die Entwicklung von Open Educational Resources (OER) auf Basis von freier Software und offenen Formaten.

Strain-gauge-based measurements of ice loads on ships

Till Zorn
Design loads are a central element of ship construction, because they influence plate and frame thickness. For the construction of ships that are destined to navigate in cold areas, it is extremely important to take into account the loads of ice impacts and their location on the hull. But ice is a particularly inconsistent material. To measure ice-induced loads, a lot of measurement has been undertaken, many of them used strain gauges. However, long-term strain...

The JamBerry - a stand-alone device for networked music performance based on the Raspberry Pi

Florian Meier, Marco Fink & Udo Zölzer
Today’s public Internet availability and capabilities allow manifold applications in the field of multimedia that were not possible a few years ago. One emerging application is the so-called Networked Music Performance, standing for the online, low-latency interaction of musicians. This work proposes a stand-alone device for that specific purpose and is based on a Raspberry Pi running a Linux-based operating system.

Low-latency audio over IP on embedded systems

Florian Meier
Übertragung von Audiodaten über Netzwerke wie das Internet ist eine weitverbreitete Technology. Bis jetzt ist die hauptsächliche Anwendung die Übertragung von menschlicher Stimme (Voice over IP). Obwohl moderne Voice over IP Systeme dafür ausgelegt sind Latenz zu reduzieren, ist diese immer noch zu groß um bidirektional Livemusik zu übertragen. Die Entwicklung einer Musikumgebung mit niedriger Latenz würde verteilte Musikaufführungen, sowie "Jamming over IP" erlauben. Diese Arbeit geht einen Schritt in diese Richtung in dem ein...

Finite element simulation of pole vaulting

Sven Drücker, Konrad Schneider, Navneet-Kaur Ghothra & Swantje Bargmann
Pole vaulting is one of the most spectacular disciplines in athletics. The evolution of world record heights is strongly influenced by the development of advanced poles and subsequent materials. Employing advanced, load-adjusted composites has resulted in a steady increase of the world record height. This study provides a framework for finite element simulations of pole vaulting with focus on the initial and boundary conditions as well as finite element choices. The influence of the pole...

A Tale of three cities : urban culture and social change in the Palestinian West Bank

Thomas Malsch & Hilke Rebenstorf
Based on survey data of adolescents and parents from three major Palestinian cities, this article is a contribution to an ongoing debate on urban Arab culture and social change in the Middle East. Starting with a critical review of scholarly articles on the three West Bank cities of Hebron, Nablus, and Ramallah, we draw on evolutionary concepts of change from below, assuming varieties of urban modernization instead of global convergence of city cultures. In adopting...

Adsorption-induced deformation of nanoporous materials : a review

Gennady Y. Gor, Patrick Huber & Noam Bernstein
When a solid surface accommodates guest molecules, they induce noticeable stresses to the surface and cause its strain. Nanoporous materials have high surface area and, therefore, are very sensitive to this effect called adsorption-induced deformation. In recent years, there has been significant progress in both experimental and theoretical studies of this phenomenon, driven by the development of new materials as well as advanced experimental and modeling techniques. Also, adsorptioninduced deformation has been found to manifest...

Aging of a Pt/Al2O3 exhaust gas catalyst monitored by quasi in situ X-ray micro computed tomography

Georg Hofmann, Amélie Rochet, Elen Ogel, Maria Casapu, Stephan Ritter, Malte Ogurreck & Jan-Dierk Grunwaldt
Catalyst aging effects were analyzed using X-ray absorption micro-computed tomography in combination with conventional characterization methods on various length scales ranging from nm to mmto gain insight into deactivation mechanisms. For this purpose, a 4 wt% Pt/Al2O3 model exhaust gas catalyst was coated on a cordierite honeycomb and subjected to sequential thermal aging in static air at 950 C for 4, 8, 12 and 24 hours. The aging was followed on the one hand by...

Highly porous α-Al 2 O 3 ceramics obtained by sintering atomic layer deposited inverse opals

Kaline P. Furlan, Robert M. Pasquarelli, Tobias Krekeler, Martin Ritter, Robert Zierold, Kornelius Nielsch, Gerold A. Schneider & Rolf Janßen
A process for generating highly porous α-Al2O3 ceramics has been developed. In this paper, a combination of self-assembly and atomic layer deposition is demonstrated as a means to fabricate inverse alumina opals, which have their structures transformed via sintering. The resulting highly porous structure is stable even after a 4 h dwell time at 1400 °C, in contrast to structures generated by conventional powder metallurgy, sol-gel or colloidal powder suspension infiltration methods. TEM analysis reveals...

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