1,721,065 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Influence of fillers on the quasi-static mechanical properties of elastomers
No full textDie vorliegende Arbeit liefert einen Beitrag zur Beschreibung des Füllstoffeinflusses auf das quasi-statische, mechanische Verhalten von Elastomeren insbesondere unter hydrostatischem Druck. Vulkanisate aus Naturkautschuk und Styrol-Butadien-Kautschuk mit und ohne aktive sowie inaktive Füllstoffe werden untersucht. Der entscheidende Materialparameter zu einer Beurteilung dieses Füllstoffeinflusses ist der Kompressionsmodul, der sowohl vom Füllstoffgehalt als auch von der Beanspruchung anhängt. Außerdem wird ein gegenseitiger Einfluss der Belastungen beobachtet. Die Kompressibilität nimmt nach uniaxialer Beanspruchung um ca. 10 % ab, was durch das freie Volumen verursacht wird. Ebenso nimmt die volumetrische Dehnung unter Zugbelastung nach Kompression zu. Bei hydrostatischen Beanspruchungen ergeben sich Modulwerte größer 2 GPa, die mit zunehmendem Anteil an verstärkenden Füllstoffen größer werden. Der über die Querdehnung bestimmte Kompressionsmodul bei Zugbelastung nimmt um zwei Größenordnungen kleinere Werte als bei hydrostatischer Beanspruchung an. Um eine hohe Abbildungsgüte durch Finite Elemente Simulationen zu gewährleisten, sind beide Fälle bei der Materialmodellierung zu berücksichtigen. Es wird daher ein deformationsabhängiger Kompressionsmodul für den Übergang von oder zu hydrostatischer Belastung definiert. Durch einen Vergleich von Simulationen mit realen Bauteilversuchen wird gezeigt, dass eine hohe Simulationsgüte für verschiedene Belastungsfälle erreicht wird.The present work contributes to the characterisation of the filler influence on the quasi-static mechanical behaviour of elastomers in particular under hydrostatic pressure. Natural rubber and synthetic styrol butadiene rubber vulcanisates with and without waxes and at different content of carbon black are investigated. The most crucial material parameter to evaluate this influence is the material’s bulk modulus, which is shown to depend on both filler content and type of load. Furthermore, a mutual influence of these loading conditions is observed. The compressibility of NR compounds under hydrostatic load after the application of uniaxial tension reduces by 10 %, mainly caused by the influence of free volume. The volumetric strain under uniaxial tension of previously compressed NR also increases. A hydrostatic load state leads to a modulus larger than 2 GPa, increasing with the filler content. In any other case, where the rubber is not exposed to hydrostatic loads, the bulk modulus resulting from the lateral strain reduces about two orders of magnitude. To achieve a good result quality in finite element simulation both cases have to be taken into account. Therefore, a deformation dependent bulk modulus is defined in order to provide a smooth transition from and to hydrostatic stress. A comparison of simulation and experimental results of real components proves the high result quality for different load cases
Contribution to the micromechanical simulation of short fiber reinforced plastics - deformation and failure
No full textDie Finite-Elemente-Methode (FEM) hat sich in den letzten Jahren als Werkzeug für die Auslegung von Konstruktionsbauteilen, ebenso wie kurzfaserverstärkte thermoplastische Kunststoffe als Konstruktionswerkstoff, fest etabliert. Im Gegensatz zum weitverbreiteten Einsatz der FEM als Werkzeug, sowie der kurzfaserverstärkten Kunststoffe als Werkstoff, sind Methoden zur effizienten Berechnung der Deformation und des Versagens dieser Verbundwerkstoffe mittels FEM nicht ausreichend entwickelt.
Im Rahmen der Arbeit wird dieser Gegensatz aufgegriffen. Es wird zunächst die prozessbedingt sich einstellende Mikrostruktur analysiert und Methoden zur analytischen Beschreibung vorgestellt. Darauf aufbauend erfolgt die Entwicklung von zwei Ansätzen zur elastisch-plastischen Modellierung kurzfaserverstärkter Kunststoffe unter expliziter Berücksichtigung der vorliegenden Mikrostruktur. Neben der Berechnung des Deformationsverhaltens steht auch das Versagensverhalten im Fokus der Arbeit. Hierzu werden, aufbauend auf die Modellierungsansätze, zwei unterschiedliche Dimensionierungsstrategien entwickelt und exemplarisch angewendet.
Die Arbeit steht im Gesamtkontext einer effizienten und verlässlichen, computergestützten Berechnung von kurzfaserverstärkten, thermoplastischen Kunststoffen. Vor diesem Hintergrund wird der Aufwand zur Kalibrierung und Umsetzung der ausgewählten Modelle und Strategien in einem entsprechenden Bewertungsschema abschließend analysiert und ausgewertet.In recent years the Finite-Element-Method (FEM) has been established as a common tool for the dimensioning of structural parts. Also, short fiber reinforced thermoplastics have been established as structural materials. However, the development of methods for the efficient computation of the deformation and failure behavior of these composite materials is insufficient and in conflict to the common use of short fiber reinforced thermoplastics as a structural material and of FEM as an engineering tool.
In the presented contribution this contrast is in focus of the considerations. The process related microstructure is analyzed and existing methods for the analytical description are presented. Based on this, two approaches for the elastic-plastic modeling of short fiber reinforced thermoplastics are developed by explicitly taking into account the existing microstructure. Besides the computation of deformation behavior, the computation of failure is of special interest. Therefore, two different dimensioning strategies are presented and are exemplarily applied to structural parts.
The contribution is seen in the context of developing an efficient and reliable, computational method for the simulation of short fiber reinforced thermoplastics. Against this background the developed models and strategies are evaluated by taking into account the effort for calibration and application and the results are summarized in an evaluation scheme
Charakterisierung und Modellierung viskoelastischer Eigenschaften von kurzglasfaserverstärkten Thermoplasten mit Faser-Matrix Interphase
Full text linkDer Einfluss mikroskopischer Eigenschaften der Faser-Matrix Interphase auf die makroskopische Verbundsteifigkeit ist für kurzfaserverstärkte Thermoplaste nicht hinreichend bekannt. Im Rahmen der vorliegenden Arbeit wird eine systematische Untersuchung der geometrischen sowie der mechanischen Eigenschaften der Interphase hinsichtlich der Beschreibung linear-viskoelastischer Effekte eines Verbundwerkstoffs durchgeführt. Die erarbeiteten Ergebnisse werden mit einem Fokus auf die Interaktion zwischen mikromechanischer Materialmodellierung und experimenteller Charakterisierung vorgestellt. Einerseits wird zur Beschreibung eines Verbundwerkstoffs mit Interphase ein zweistufiger Modellierungsansatz unter Berücksichtigung anisotroper sowie linear-viskoelastischer Effekte entwickelt. Andererseits werden die Materialparameter des Materialmodells mit experimentellen Methoden zur mikro- sowie makroskopischen Charakterisierung des Verbundwerkstoffs und dem Matrixmaterial identifiziert. Im Vergleich dieser experimentellen Ergebnisse mit den errechneten Verbundwerkstoffeigenschaften kann ein Rückschluss auf die makroskopischen mechanischen Eigenschaften des Verbundwerkstoffs in Abhängigkeit der Interphase getroffen werden. Somit wird in der vorliegenden Arbeit eine inverse Methodik vorgestellt, die mit einer direkten Verknüpfung von realistischer Materialmodellierung und experimentellen Untersuchungen einen neuen Zugang zu unbekannten Werkstoffparametern ermöglicht.In order to improve the mechanical properties of short fiber composites, the fiber-matrix adhesion is decisive and depends strongly on the intersection region between the fiber and the matrix material. However, no perspicuous information about the influence or mechanical properties of the fiber-matrix interphase in short fiber reinforced thermoplastic composites is available. Thus, the present thesis aims for a systematic identification of the geometrical and mechanical impacts of an interphase on the linear-viscoelastic behavior in short glass fiber reinforced thermoplastics. Thereby, the performed investigations are focused on the interaction between micromechanical material modeling and experimental testing. On the one hand, a two-step modeling approach is developed for the realistic description of an entire three phase composite with interphase including anisotropic and linear-viscoelastic effects. On the other hand, the input of this model is provided by different experimental testing methods ranging from the micro- to the macroscale characterization of the composite and matrix material. By comparing these experimental results with the linear-viscoelastic modeling output, the impact of the interphase on the mechanical properties of the composite is accessible. Thus, it is shown that a realistic material modeling and experimental investigations are closely interlinked
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Beitrag zur Beschreibung des mechanischen Langzeitdeformationsverhaltens von thermoplastischen Kunststoffen
Full text linkDie Finite Elemente Analyse (FEA) hat sich in den letzten Jahren als Werkzeug für die Bauteilauslegung fest etabliert. Die Berechnung des Langzeitverhaltens von Kunststoffbauteilen stellt hierbei immer noch eine große Herausforderung dar. Gängige FEA-Programme verfügen zwar über eine Vielzahl von unterschiedlichen Materialmodellen, die jedoch nur bedingt in der Lage sind, die stark nichtlineare Zeit-, Temperatur- und Lastabhängigkeit des mechanischen Werkstoffverhaltens der Kunststoffe in guter Näherung darzustellen. Darüber hinaus stehen für die Berechnung oftmals nur wenige Werkstoffdaten zur Verfügung. Diese Arbeit stellt eine Methode vor, mit der das mechanische Werkstoffverhalten von Kunststoffen über einen weiten Last-, Temperatur- und Zeitbereich abgebildet werden kann. Die Methode beinhaltet eine Erweiterung eines linear viskoelastischen Materialmodells sowie die Auswertung und Aufbereitung der Messdaten zu dessen Kalibrierung. Basierend auf um-fangreichen Untersuchungen werden werkstoffgerechte Annahmen getroffen, die es ermöglichen, das Materialmodell bereits anhand von uniaxialen Zugkriechdaten ausreichend zu kalibrieren. Da diese Daten meist in Werkstoffdatenbanken hinterlegt sind, kann somit auf Basis dieser vorliegenden Daten, die gegebenenfalls durch Kurzzeitzugkriechdaten ergänzt werden müssen, eine verbesserte Berechnung des temperatur- und lastabhängigen Langzeitverhaltens von Kunststoffkomponenten erzielt werden.In the past years the Finite Element Analysis (FEA) has established as a tool for the dimen-sioning of plastics parts. The simulation of the mechanical longterm behaviour with this tool is still a challenging task. Common FEA tools indeed offer a number of material models, but these models can not sufficiently represent the time, load and temperature dependency of the mechanical longterm behaviour of plastics. Furthermore, there are just few material data available in material databases to calibrate the material models. This thesis presents a method to simulate the mechanical longterm behaviour of polymers over a wide range of time, temperature and load. The method includes a modification of a linear viscoelastic model and a procedure for the model calibration. On the basis of extensive experiments assumptions are made, which enable a calibration of the model on the basis of uniaxial tensional creep data, which are most of the time available in material data bases. Therefore an improvement of the simulation of plastics components can be achieved on the basis of available material data which, if necessary, are complemented by some shortterm creep data
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Otomotiv uygulamaları için kompozit-metal yapılarda intrinsik bağlantı arayüzü geliştirilmesi
Full text linkYirmi birinci yüzyılda hafif konstrüksiyon tasarımları farklı alanlara uygulanabilirliği, yakıt tasarrufu ve güvenli sürüş amaçları sebebiyle büyük talep görmektedir. Kompozit malzemeler yüksek birim başına dayanım kuvveti sebebiyle bir hafif malzeme olarak havacılık, otomotiv ve denizcilik sektörlerinde yaygın kullanımdadır. Kompozit parçaları diğer parçaları bağlamak için kullanılan yaygın bir bağlantı yöntemilerinden biri delik delerek cıvatalamadır. Ancak, cıvatalama kompozit malzemenin delinmesini gerektirmektedir ki bu malzemenin dayanımını ciddi ölçüde azaltır. Cıvata bölgesini güçlendirmek ve delme işlemi olmaksızın cıvata deliği oluşturma imkanı sağlayan bir yöntem kompozitin üretimi sırasında cıvata deliği bölgesine kompozitin tabakaları arasına insert yerleştirmedir. Bu tez çalışmasında bir Mercedes benz kamyon parçasının bağlantı bölgesi için üç farklı tip güçlendirme insert'ü tasarlanmıştır. Bunlar metal insert, termoplastik insert ve metal-termoplastik hibrit insert'lerdir. Buna ek olarak, dört tip düz örgü cam elyaf-epoxy kompozit numune üretilmiştir. Bunların üç tanesinin tabakaları arasında insert yerleştirilmişl, bir tanesi delinmiş ve referans olması için insert'süz bırakılmıştır. Numunelere yarı durağan yükleme koşullarında pin çekme testi uygulanmıştır. Test sonuçlarına göre tüm insert'lü kompozit numunelerin son yük taşıma kapasitelerinin arttığı gözlenmiştir (en çok %44 artış). Ek olarak, delinmemiş kompozit numunelerin delik bölgelerinin mukavemetinin referans numuneye göre %74 seviyesinde güçlendiği gözlenmiştir. Öte yandan, insert yerleştirilmiş numunelerin katmanlarında ciddi birbirinden ayrılma gözlenmiştir (3mm'ye kadar). Hepsine ek olarak, testler sonlu elemanlar analizi programı Abaqus'ta modellenmiştir. Analiz ve test sonuçları arasındaki tokluk hatası referans numune için sadece %5, metal insert'lü numune için %39.2 seviyesindedir. Ne yazık ki, elastik bölge sonrası malzeme özellikleri sonlu elemanlar analizi sonucunda iyi seviyede yakınsamamıştır.The lightweight construction is in great demand in the 21st century with the increasing need for fuel saving, safety concerns and customized material properties. For its high specific strength and customizable material properties, the composite materials have found its place as a major lightweight material in aerospace, marine and automotive industries. One fastening technique to join these composite parts to other components is bolted joining which requires drilling to form the holes. Nevertheless, drilling weakens the properties of the composite enormously. One technique to reinforce the joint is to place inserts in the bearing region during the production of the composite. In this work, three different reinforcement inserts were designed for joint region of a Mercedes-Benz Truck component, namely metal insert (M), polymer insert (P) and metal- polymer insert (MP). Four different types of glass/epoxy, plain weave textile composite (PWTC) specimens were designed. One specimen type is only drilled which is used as reference, and other three specimen types have inserts embedded between their layers. The specimens were tested under quasi-static loading conditions at a two-parallel pinned pull-through test. It is observed that all the inserted specimens have higher ultimate load capacity relative to the reference specimens (up to 44% improvement). Besides, the bearing strength increases up to 74.7% at the non-drilled specimen types. However, placement of inserts leads to significant delamination failure (up to 3mm delamination at polymer inserted specimen). Moreover, the pin pull-through test of reference specimen and metal inserted specimen were modeled in commercial Abaqus FEA software. Stiffness values from FE analysis is in relatively good correlation with experimental stiffness. The stiffness errors for reference and metal inserted specimens are 5% and 39.2% consequently. The non-elastic response of PWTC specimens were not properly represented in the FE models
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