620 Ingenieurwissenschaften und Maschinenbau
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Innerhalb eines Forschungsprojektes wurde ein Energiesystemoptimierungsmodell entwickelt, das mögliche Geschäftsmodelle als Weiterbetriebsoptionen für Biogasanlagen betrachtet. Insbesondere der Einfluss von fluktuierenden Strommarktpreisen und variierenden Treibhausgasquoten soll kritisch im innerdeutschen Kontext beleuchtet werden.
Reibermüdung ist ein Phänomen, welches an den Kontakträndern von in Berührung ste-henden, kraftübertragenden Bauteilen beobachtet werden kann. Typische Maschinenele-mente, die in diesem Mode versagen können, sind z. B. die Schwalbenschwanzverbindung sowie ihre Ableger, die mehrzahnigen Tannenbaumfixierungen. In der Literatur beschrie-bene Untersuchungen weisen für Flachproben mit Reibbrücken ein Lebensdauerverhalten mit einem lokalen Minimum über der Anpresskraft der Reibbrücken aus. Die vorliegende Arbeit untersucht mithilfe des Sines-Ermüdungskriteriums, kombiniert mit Grenzwerten gemäß FKM-Richtlinie, ob ein solches Verhalten auch für die Schwalbenschwanzverbin-dung zutrifft. Im Gegensatz zur Reibbrückenanordnung mit separater Einleitung von kon-stanter Pressung und Längslastamplitude fluktuieren bei der Schwalbenschwanzverbin-dung die Anpresskraft und Zugkraft mit der einzigen am Hals eingeleiteten Last.
A systematic study was performed to understand the effects of the devulcanizing agent dibenzamido diphenyl disulfide (DBD) on the vulcanization and devulcanization process of a sulfur-cured ethylene-propylene-diene monomer (EPDM) rubber. The influence of DBD on vulcanization was investigated by mixing DBD with virgin rubber and curative system. The devulcanization of rubber waste was achieved with varying amounts of DBD ranging from 0.4 to 13.8 wt% and temperatures from 150 to 200°C. The quality of vulcanizates and devulcanizates was evaluated by rheometer tests, temperature scanning stress relaxation measurements, and analysis of mechanical properties. During vulcanization, DBD acts as an accelerator in the presence of sulfur. When accelerators are added, the scorch time increases, and the cure rate decreases. Thus, DBD acts as a retarder. In the presence of activators, DBD leads to a significant reduction of crosslink density. This results in composites with high elongation at break and poor compression set values. The efficiency of the devulcanization of rubber waste depends strongly on DBD concentration and temperature. The monosulfidic crosslinks are cleaved by low concentrations of DBD, while polysulfidic crosslinks require higher concentrations. These results show that DBD is effective as a devulcanizing agent and degrades the network below 200°C.
In this experimental work, the quasi static and fatigue properties of a 40 wt.% long carbon fiber reinforced partially aromatic polyamide (Grivory GCL-4H) were investigated. For this purpose, microstructural parameter variations in the form of different thicknesses and different removal directions from injectionmolded plates were evaluated. Mechanical properties decreased by increasing misalignment away from the melt flow direction. By changing the specimen thickness, no change in the general fiber distribution pattern transversal and normal to the axis of melt flow was observed. It has shown that with increasing specimen thickness the quasi static properties along the melt flow direction decreased and vice versa resulting in superior properties normal to the melt flow axis. At around 5 mm, an intersection suggests quasi-isotropic behavior. In addition, the fatigue strength of the material was significantly higher in the flow direction than normal to the flow direction. No change in fatigue life was observed while changing specimen thickness. The Basquin equation seems to describe the effect of stress amplitude on the fatigue strength of this composite. Scanning electron microscopy was used to investigate fracture surfaces of tested specimens. Results show that mechanical properties and morphological structures depend highly on fiber orientation.
Der nachfolgende Projektbericht, welcher im Rahmen des Masterprojektes und des Moduls „Bildgebende Sensortechnik“ erarbeitet wurde, ist wie folgt den beiden Fächern zuzuordnen.
Die Kapitel, welche sich mit der Inbetriebnahme und den Umgang des SICK RMS320 Radarsensors beschäftigen, sind Teil des Masterprojektes. Dies betrifft die Kapitel 2.2, 4.1, 4.3 und in Teilen das Kapitel 4.5.
Dem Modul „Bildgebende Sensortechnik“ sind hingegen die Messung des Einflusses von Kleidung auf die Erkennungsfähigkeit eines Menschen sowie die Radarmessungen der verschiedene Prüfkörper zuzuordnen. Dies wird in den Kapiteln 2.3, 3, 4.2, 4.4 und 4.5 behandelt.
Die „Grundlagen der Radartechnik“ sind für beide Teile gleichbedeutend wichtig.
The aim of this study was to provide a systematic overview of available pressure ulcer prevention quality indicators and to evaluate the underlying empirical evidence. A systematic mapping review was conducted with combined searches in Embase and Medline, and websites of relevant institutions and organisations. The eligibility criteria were clear use of the term “quality indicator” regarding pressure ulcer prevention; English or German language; and all settings, populations, and types of resources, including articles, brochures, and online material. In total, n = 146 quality indicators were identified. Most indicators were published in the United States (n = 50). The majority of indicators was developed for the hospital setting (n = 102). Process indicators were the most common (n = 71), followed by outcome indicators (n = 49). Less than half of identified indicators appeared to be practically used. Evidence supporting the validity and reliability were reported for n = 25 and n = 30 indicators respectively. The high number of indicators demonstrate the importance of measuring pressure ulcer prevention quality. This is not an indicator of our ability to accurately measure and evaluate this construct. There is an urgent need to develop evidence-based and internationally comparable indicators to help improve patient care and safety worldwide.
In dieser Arbeit wird untersucht, wie sich ein steigender energetischer Autarkiegrad eines speziellen containerbasierten Einfamilienhauses auf verschiedene ökologische Indikatoren auswirkt. Zur Steigerung des Autarkiegrades wurden folgende Komponenten verbaut und variiert: Photovoltaik (PV) mit und ohne Batteriespeicher sowie Vakuum-Isolations-Paneelen (VIP) und Phasenwechselmaterialien (PCM) in der Gebäudehülle. Bei der Betrachtung der Umweltbelastungen stehen dabei die folgenden Lebenswegphasen im Vordergrund: Herstellung, Nutzung und Verwertung. Das Recycling Potenzial spielt hier eine untergeordnete Rolle. Nach der Definition des Gebäudes und der Ermittlung der Wärme und Strombedarfswerte werden die Ergebnisse für die verschiedenen Umweltindikatoren einzeln errechnet. Das Treibhauspotenzial (GWP), Versauerungspotenzial (AP) und der abiotische Ressourcenverbrauch werden in Abhängigkeit vom Autarkiegrad dargestellt. Die Ergebnisse zeigen, dass die ökologisch günstigste Lösung je nach Umweltindikator sehr unterschiedlich ausgeprägt ist und zwischen 0 bis 75 % Autarkiegrad liegt. Abschließend findet eine kurze ökonomische Betrachtung statt.
A suspension of PMMA spheres in a density matched saccharose solution is investigated with a classical Searle rheometer and a NMR (Nuclear Magnetic Resonance) spectrometer. Here the NMR is used to measure the radial distribution of the PMMA spheres in the rotating cell, in addition to the local velocity profile of the suspension. The influence of particle concentration on the wall depletion is studied. Further analysis are carried out with computational fluid dynamics software. The velocity field as well as the solid distribution in the couette flow is simulated with a two-phase model including the Darcy law and compared to the experimental data.
The simulation of the residual stress field achieved by shot peening cannot be carried out on component-large models. Hence, an efficient unit cell model for the simulation of the shot peening process is developed. The model allows both, the simple inclusion of a pre-stress and the evaluation of the up-arching of the Almen strip. For this purpose, generalized coupling constraints for the periodic boundaries of the unit cell are developed. These allow for displacement and rotation of the coupled boundaries relative to each other. In the coupling constraints, this is accomplished by respective variables, which can either be prescribed to the analysis or read out as a result from the analysis. Hence, the unit cell can expand, shear, bend and twist under driving forces like, e. g., residual stresses or thermal effects. At the same time, deformations of the cell’s periodic boundary pairs are kept congruent by the generalized coupling. The ability to cover expansion is novel regarding known periodic boundary conditions. Also, the application of a generalized unit cell to shot peening is new.
Results obtained with the generalized unit cell are displayed, demonstrating its capabilities: A fundamental analysis of the residual stress field from shot peening shows inhomogeneities at a fatigue relevant level to be inevitable. A validation of the model was done by comparison with experimental Almen strip shot peening tests reported in literature. Shot peening under pre-stress is demonstrated and its results in terms of residual stress are evaluated. The application of the generalized unit cell is not limited to shot peening.