32 research outputs found
"Inducing and Miscarriage": Women-Centered Perspectives on RU-486/Prostaglandin as an Early Abortion Method
No full textMarge Berer analyzes the information available from France on women's
perspectives on their use of RU 486/prostaglandin in comparison with vacuum
aspiration. The latter part of the article calls for further exploration of
women's perspectives on using this method and suggests that the information
from such research would provide a basis for resolving disagreement among
reproductive health professionals and activists and a better idea of what
women think the future of abortion technology should be. The author cautions
that in spite of the widespread agreement that acceptability studies are
central to the development of new reproductive techniques and procedures, the
research on what women find acceptable and how they experience treatments
remains at an early stage. There was much discussion at the December 1991
conference, for example, of whether women might favor medical abortion because
it puts them in charge of the process, while surgical abortion leaves them the
passive subjects of bodily intrusions
Size-Induced Constraint Effects on Crack Initiation and Propagation Parameters in Ductile Polymers
No full textFracture mechanics are of high interest for the engineering design and structural integrity assessment of polymeric materials; however, regarding highly ductile polymers, many open questions still remain in terms of fully understanding deformation and fracture behaviors. For example,
the influence of the constraint and specimen size on the fracture behavior of polymeric materials is still not clear. In this study, a polymeric material with an elastic plastic deformation behavior (ABS, acrylonitrile butadiene styrene) is investigated with regard to the influence of constraint and specimen size. Different single-edge notched bending (SENB) specimen sizes with constant geometrical ratios were tested. The material key curve was used to investigate differences in the constraint, where changes for small and large specimen sizes were found. Based on a size-independent crack resistance curve (J–R curve), two apparent initiation parameters (J0.2 and Jbl) were determined, namely, the initiation parameter Jini (based on the crack propagation kinetics curve) and the initiation parameter JI,lim (based on an ESIS TC 4 draft protocol). It was found that J0.2 and Jbl could be used as crack initiation parameters whereby Jini and JI,lim are indicative of the onset of stable crack growth
Injection Molding Simulation of Polyoxymethylene Using Crystallization Kinetics Data and Comparison with the Experimental Process
No full textIt is well known that the processing conditions in polymer processing have a high impact on the resulting material morphology and consequently the component's mechanical behavior. However, especially for semicrystalline polymers, the tools available for predicting the final morphology of injection molding parts still have significant limitations. In order to investigate the potential of injection molding simulation for the prediction of the morphology, POM homopolymer specimens were injection molded. The crystallization kinetics data were measured, and simulations in 3D and 2.5D with and without crystallization analysis were conducted in Autodesk Moldflow. The simulations are found to be good accordance with the experiments. Predicted spherulite size and crystalline orientation factor reveal a good qualitative correlation with optical micrographs. Also, the evolution of these parameters along the flow path is plausible. The simulation is found to be a powerful tool for morphology prediction in polymeric parts. Its applicability, however, is still limited to 2.5D models in Autodesk Moldflow, which, of course, is insufficient for complex, thick-walled 3-dimensional parts
J-testing of polymers via the load separation criterion based ESIS TC4 procedure: Effect of the specimen size
No full textThe Technical Committee 4, "Polymers, Polymer Composites and Adhesives", of the European Structural Integrity Society (ESIS TC4) developed a draft protocol based on the load separation criterion to determine two fracture parameters (an initiation parameter, J(I,lim) and a crack growth parameter, m(s)) without the need to measure the crack growth (Delta a). This is especially beneficial, since the measurement of Delta a is prone to errors. The developed testing scheme displays promising results, as shown in a round-robin testing exercise. To further push this testing scheme, it is necessary to verify the specimen size scaling possibility. Hence, in this work, single edge notched in bending (SE(B)) specimens with different sizes, but geometrically similar, were manufactured. ESIS TC4 testing scheme was successfully applied to specimens with the different sizes, and data of J(I,lim) and m(s) were obtained. The observed effect of the specimen size on the aforementioned fracture parameters is presented and discussed
Development of a new type of sealing system for a helicopter gearbox
No full textZiel dieser Arbeit ist es, ein innovatives Dichtungssystem für die Antriebswelle eines Helikopters zu finden. Diese Dichtung stellt im Allgemeinen bei vielen Hubschraubergetrieben ein Problem durch Getriebeöl-Leckagen dar. Konkret wird auf das Getriebe des Eurocopter EC135, heutige Bezeichnung Airbus Helicopters H135, eingegangen. Bekanntheit hat dieses Helikoptermodell vor allem durch den Einsatzzweck als Rettungshubschrauber der Christophorus-Flotte sowie den Einsatz als Polizeihubschrauber erlangt. Bei diesem Modell wird die Getriebeeingangswelle mittels herkömmlicher Radialwellendichtring abgedichtet, dieser hat nur bedingte Lebensdauer und führt daraus resultierend zu erhöhten Leckageraten sowie erhöhtem Wartungsaufwand. Da die üblichen Eingangsdrehzahlen im Bereich von 6000 U/min liegen, wird ein berührungsloses Dichtungskonzept für den Betriebsfall angestrebt. Durch methodisches Bewerten von am Markt verfügbaren Dichtungssystemen sowie eines Eigenkonzeptes wird das am besten geeignete Dichtungssystem für diesen Anwendungsfall gefunden.Die Eigenkonzeptionierung überzeugt mit den Eigenschaften in allen Betriebsbereichen nahezu leckagefrei zu arbeiten, sowie wartungsfrei und verschleißarm zu sein. Dies ist möglich durch eine berührungslose Labyrinthdichtung für den Nennbetrieb, sowie eine berührende Stillstanddichtung für den Wellenstillstand und Bereich geringer Drehzahlen. Diese hebt ab einer bestimmten Drehzahl durch einen Fliehkraftmechanismus ab, ohne extern benötigter Steuerung. Anhand eines Kunststoff 3D-Druckes des ausgearbeiteten Dichtungskonzeptes wird die Auslegung und Berechnung des Abhebemechanismus der Stillstanddichtung validiert.The aim of this work is to find an innovative sealing system for the drive shaft of a helicopter. This seal is generally a problem in many helicopter gearboxes due to gearbox oil leaks. Specifically, the gearbox of the Eurocopter EC135, now known as the Airbus Helicopters H135, is examined. This helicopter model is best known for its use as a rescue helicopter in the Christophorus fleet and as a police helicopter. In this model, the transmission input shaft is sealed using a conventional radial shaft seal, which has only a limited service life and therefore leads to increased leakage rates and higher maintenance costs. Since the usual input rotation speeds are in the range of 6000 rpm, a non-contact sealing concept is aspired for the operating case. The most suitable sealing system for this application is found by methodically evaluating sealing systems available on the market as well as an in-house concept.The in-house design impresses with its properties of being virtually leak-free in all operating ranges, as well as being maintenance-free and low-wear. This is made possible by a non-contacting labyrinth seal for nominal operation, as well as a contacting standstill seal for standstill and low speed range. This sealing system lifts off, due to a centrifugal mechanism, at a certain speed, without an external control mechanism. The design and calculation of the lift-off mechanism of the standstill seal is validated using a plastic 3D print of the developed seal concept
Byzantine perceptions of the outsider in the eleventh and twelfth centuries : a method
No full textThis thesis examines the portrayal of outsiders in Michael Psellos's Chronographia, Anna Komnene's Alexiad, and
Niketas Choniates's Narrative - using sociological theories of deviancy. The
twofold aim is to "treat texts seriously", localized in Jakobson's speech-event
nexus of addresser, context, content, contact, code and addressee; and
secondly to understand the texts as statements of the ideology of the
dominant elite.
Outsiders are defined (using the labelling orientation) as people
successfully defined as deviants; deviant behaviour is whatever they do. The
dominant elite creates cultural boundaries, and places individuals in outsider
roles on the other side of those boundaries. Outsiders can be understood only
in terms of who defines them as deviant; there is no material reality to
deviancy. Stereotypes, which identify social categories of people by evaluative
trait-characteristics, are necessary elements of human cognition; they become
prejudice only when they are over-generalized, based on too limited data,
applied too widely and maintained in the face of contrary empirical evidence.
The analysis of the three texts in depth allows the identification of those
groups labelled as outsiders by these expositors of the dominant ideology. My
conclusion is that these authors portray a picture of the Byzantine outsider,
which is coherent between this limited sample group, allowing for individual
variation. These authors used stereotypes to conceptualize and encode in the
linguistic and lexicographical complexities of their texts the outsiders they
identified in their societies. Their presentation uses stereotypes, but does not
descend to prejudice
Fracture of Thin-Walled Polyoxymethylene Bulk Specimens in Modes I and III
No full textThin-walled polymeric components are used in many applications. Hence, knowledge about their fracture behavior in bulk is beneficial in practice. Within this study, the double cantilever beam (DCB) and out-of-plane double cantilever beam (ODCB) tests are enhanced to enable the testing of such bulk specimens in mode I and mode III on the basis of the J-integral. This paper then presents and discusses the experimental results following the investigation of a semicrystalline polymer (polyoxymethylen) under quasi-static load conditions. From the experiments, fracture energies of similar magnitude in both mode I and mode III were determined. In mode III, pop-in fracture was observed. Furthermore, the fracture surfaces were investigated regarding the mode I and mode III dominant crack growth mechanisms, based on the morphology of the tested material. For specimens tested in mode I, no signs of plastic deformation were observed, and the fracture surface appears flat. In mode III, some samples display a twisted fracture surface (twisting angle close to 45°), which indicates local mode I crack growth. A transfer of the presented methodology to other (more ductile) polymeric materials is deemed possible without further restrictions. In addition, the presented setup potentially enables an investigation of polymeric bulk specimens in mixed mode I+III
Methods for automated crack length detection in fracture mechanical fatigue tests of unreinforced polymers
No full textprinting
No full textOsterreichische Forschungsforderungsgesellschaft; Austrian Government; State Governments of Styria, Lower Austria and Upper Austri
