Test anxiety is an individual personality trait, which results in elevated state anxiety in situations of performance evaluation. For school-age children, high-stakes examinations occurring at the culmination of programmes of study are where they frequently experience such evaluation. Alongside its impact on an individual's wellbeing, heightened test anxiety has been reliably linked to deficits in performance on examinations and assessments. Attentional bias has been shown to be an aspect of many forms of anxiety and is considered to have role in the maintenance of state anxiety, though the mechanisms underlying this are not fully clear. However, Attentional Control Theory (Eysenck, Derakshan, Santos, & Calvo, 2007) implicates preferential allocation of attention to threat in its explanation of performance deficits associated with test anxiety. The presence of attentional bias in test anxiety appears theoretically plausible with some empirical support (e.g. Putwain, Langdale, Woods and Nicholson, 2011); however, its reliability is under question. This study aims to investigate the presence of attentional bias in test anxiety, with a view to further understanding its underlying mechanisms and informing the development of interventions to ameliorate its effects. To ensure ecological validity, this study was conducted in schools and colleges, with a sample of 16-18-year olds following high-stakes programmes of study. Full investigation of test anxiety requires individuals to experience heightened state anxiety through performance evaluation threat; hence, the Trier Social Stress Test (TSST) was modified to make it applicable to this context and population. This study was conducted in two experimental phases, both of which adopted a mixed methodological approach to provide quantitative and qualitative data. The preliminary phase evaluated the materials and anxiety manipulation protocols. The main phase employed the modified-TSST in collaboration with a dot-probe task to investigate participants' attentional bias when under high performance evaluation threat. No patterns of attentional bias were uncovered to indicate a consistent relationship to either trait test anxiety or attentional control. However, there was a level of congruence between how some individuals describe themselves in evaluative situations and the attentional bias they displayed. Further investigation employing mixed methodological approaches such as Single Case Experimental Design is recommended to identify and address attentional bias in test anxiety.

Fatigue failure of metallic structures operating under dynamic loading is a common occurrence in engineering applications. It is difficult to estimate the response of complicated systems analytically, due to structure&amp / #8217 / s dynamic characteristics and varying loadings. Therefore, experimental, numerical or a combination of both methods are used for fatigue evaluations. Fatigue failure can occur on systems and platforms as well as components to be mounted on the platform. In this thesis, a helicopter&amp / #8217 / s Missile Warning Sensor - Cowling assembly is analyzed. Analytical, numerical and experimental approaches are used wherever necessary to perform stress and fatigue analyses. Operational flight tests are used for obtaining the loading history at the analyzed location by using sensors. Operational vibration profiles are created by synthesizing the data (LMS Mission Synthesis). Numerical fatigue analysis of the assembly is done for determining the natural modes and the critical locations on the assembly by using a finite element model (MSC Fatigue). In addition, numerical multiaxial PSD analysis is performed for relating the experimental results (Ansys). Residual stresses due to riveting are determined (MSC Marc) and included in experimental analysis as mean stresses. Bolt analysis is performed analytically (Hexagon) for keeping the v assembly stresses in safe levels while mounting the experimental prototype to the test fixture. Fatigue tests for determining the accelerated life parameters are done by an electromagnetic shaker and stress data is collected. Afterwards, fatigue test is performed for determining whether the assembly satisfies the required operational life. Resonance test is performed at the frequency in which the critical location is at resonance, since there was no failure observed after fatigue testing. A failure is obtained during resonance test. At the end of the study, an analytical equation is brought up which relates accelerated life test durations with equivalent alternating stresses. Therefore, optimization of the accelerated life test duration can be done, especially in military applications, by avoiding the maximum stress level to reach or exceed the yield limit.

nÃo hà / A execuÃÃo de um projeto de fundaÃÃes superficiais requer um estudo prÃvio do subsolo de assentamento. Tal estudo inclui a estimativa da tensÃo admissÃvel e a previsÃo dos recalques aos quais a estrutura se submeterÃ. Para a previsÃo do comportamento mecÃnico, sÃo necessÃrias investigaÃÃes que tanto podem ser de campo como de laboratÃrio. Nesse contexto, o ensaio de prova de carga direta à uma alternativa interessante, pois, atravÃs dele, o comportamento da futura fundaÃÃo à reproduzido em escala praticamente real. O presente trabalho trata do estudo do comportamento de fundaÃÃes superficiais assentes em subsolos, da cidade de Fortaleza, arenosos de baixa compacidade, cuja previsÃo do comportamento à feita correntemente atravÃs de sondagens à percussÃo (SPT). A metodologia adotada no presente trabalho consiste na coleta de dados de ensaios de placa e sondagens à percussÃo em uma empresa local, coleta de amostras deformadas e caracterizaÃÃo geotÃcnica em laboratÃrio dos solos presentes nos locais de ensaio, previamente escolhidos, realizaÃÃo de provas de carga direta com placas de trÃs diÃmetros diferentes (30, 50 e 60 cm), e, por fim, realizaÃÃo de anÃlises com o objetivo de avaliar o desempenho de solos arenosos de baixa compacidade atravÃs de mÃtodos consagrados para a previsÃo da tensÃo admissÃvel, do recalque e do coeficiente de reaÃÃo vertical. A partir daÃ, foi possÃvel avaliar o desempenho de diversos mÃtodos, usualmente utilizados, em projetos de fundaÃÃes superficiais na prÃtica de Fortaleza. Foi observado que a sondagem à percussÃo (SPT) nÃo à um ensaio apropriado para a previsÃo do comportamento de solos arenosos de baixa compacidade de Fortaleza. Nesses casos, a previsÃo da tensÃo admissÃvel deve ser feita pela realizaÃÃo de ensaios mais acurados como provas de carga direta, ensaio de cone (CPT) ou, atà mesmo, com o ensaio pressiomÃtrico. AlÃm disso, quanto ao coeficiente de reaÃÃo vertical, o ensaio de prova de carga direta forneceu resultados superiores aos obtidos de correlaÃÃes com o Ãndice de resistÃncia à penetraÃÃo (NSPT) de sondagens à percussÃo. Por fim, em relaÃÃo à estimativa de recalques, o mÃtodo semi-empÃrico de DÃcourt (1992) foi o que apresentou o melhor desempenho. / The implementation of a project of shallow foundations requires a prior study of the subsoil. This study includes an allowable stress estimative and prediction of settlements to which the structure will be subjected. To predict the mechanical behavior, investigations are required which can be both field and laboratory. In this context, the plate test is an interesting alternative because, through it, the future behavior of foundation is reproduced in virtually real scale. The present work deals with the study of the behavior of shallow foundations on soils in Fortaleza city, which are sandy low compactness, whose behavior prediction is done currently through the standard penetration test (SPT). The methodology adopted in this study consists of collecting data from plate test and standard penetration test in a local company; collecting disturbed samples in test sites and doing geotechnical characterization of soils in laboratory, previously chosen; performing plate tests with three different diameters (30, 50 and 60 cm), and, finally, analyzing in order to evaluate the performance of sandy soils of low compactness through established methods for predicting the admissible stress, the settlement and coefficient vertical reaction. From there, it was possible to evaluate the performance of several methods commonly used in projects of shallow foundations in practice in Fortaleza city. It was observed that the standard penetration test (SPT) is not an appropriate test for predicting the behavior of sandy soils of low compactness of Fortaleza. In these cases, the prediction of the allowable stress should be made by using more accurate tests like plate tests, cone test (CPT) or even the pressuremeter test (PMT). Moreover, as the coefficient of vertical reaction, the plate test provided superior results to those obtained from correlations with the SPT resistance (N-value). Finally, in relation to the estimation of settlements, the semiempirical method of DÃcourt (1992) showed the best performance.

L’amélioration des systèmes de conversion d’énergie rend les dispositifs à base de SiC très attractifs pour leur efficacité, compacité et robustesse. Cependant, leur comportement en réponse à un défaut de court-circuit doit être soigneusement étudié pour assurer la fiabilité des systèmes. Ce travail de recherche porte sur les problèmes de robustesse et de fiabilité du MOSFET SiC sous contraintes de court-circuit. Cette étude repose sur des caractérisations électriques et microstructurales. La somme de toutes les caractérisations avant, pendant et après les tests de robustesse ainsi que l’analyse microstructurale permet de définir des hypothèses sur l’origine physique de la défaillance pour ce type de composants. De plus, la mesure de la capacité est introduite au cours des tests de vieillissement en tant qu’indicateur de santé et outil clé pour remonter à l’origine physique du défaut. / The improvement of power conversion systems makes SiC devices very attractive for efficiency, compacity and robustness. However, their behavior in response to short circuit mode must be carefulli studied to ensure the reliability of systems. This research work deals with the SiC MOSFET robustness and reliability issues under short-circuit constraints. It is based upon electrical and microstructural characterizations. The sum of all the characterizations before, during and after the robustness tests as well as microstructural analysis allow to define hypotheses regarding the physical origin of failure of such components. Also, caoacitance measurement is introduced during aging tests as a health indicator and a key tool to go back to the physical origin of the defect.

No description available.

Der Verbundwerkstoff Stahlbeton zeichnet sich durch das effektive Zusammenwirken seiner beiden Einzelkomponenten Stahl und Beton aus. Dieses wiederum kann nur durch ausreichend gute Verbundbedingungen zwischen beiden Baustoffen gewährleistet werden. Die Verbundeigenschaften werden von zahlreichen Faktoren beeinflusst, zu denen u.a. die Oberflächenprofilierung des Stahls, die Betonfestigkeit und die Umschnürungswirkung durch den umgebenden Beton oder eine Querbewehrung zählen. Auch eine quer zum Stab angreifende Belastung kann einen erheblichen Einfluss auf den Verbundmechanismus und die Verbundversagensart haben. Bei Stahlbetonbauteilen unter einer zweiaxialen Zugbelastung, wie sie z.B. in Behälterwänden oder zweiachsig gespannten Platten auftritt, unterliegt die Bewehrung sowohl einer Längszug- als auch einer Querzugbeanspruchung. Im Rahmen der vorliegenden Arbeit wurde der Einfluss einer Querzugbelastung auf das Verbundverhalten zwischen Rippenstählen und Normalbeton mit Hilfe von würfelförmigen Ausziehkörpern mit einer kurzen Verbundlänge untersucht. Dabei lag das Querzugniveau stets unterhalb der Risslast des Betons, so dass keine Risse entlang des einbetonierten Stabes auftraten. Neben der Höhe der Querzugbelastung wurden im Versuchsprogramm die Betonfestigkeit, der Stabdurchmesser und die Betondeckung variiert. Anhand der Versuchsergebnisse konnte gezeigt werden, dass sich auch unter einer Querzugbelastung der Verlauf der Verbundspannungs-Schlupf-Beziehung nicht ändert. Die Art des Verbundversagens wird jedoch maßgeblich durch den Querzug beeinflusst, welcher ein Spaltbruchversagen in jedem Fall begünstigt. Mit steigendem Querzug tritt auch bei großen Betondeckungen statt eines Ausziehversagens ein Spaltbruchversagen ein. Mittels des vorgeschlagenen Berechnungsmodells können in Abhängigkeit des Querzugniveaus und der Größe der Betondeckung Grenzlinien für den Wechsel im Verbundversagensmodus bestimmt werden. Hierbei wurde ebenfalls der Einfluss der Probekörpergeometrie auf die Versuchsergebnisse in die Berechnung einbezogen, so dass die angegebenen Grenzlinien auch für reale Einbettungslängen der Bewehrung gelten. Weiterhin wurde anhand der Versuchsdaten sowie eines Datensatzes aus der Literatur ein Verbundmodell für kurze Verbundlängen entwickelt, das den Einfluss der bezogenen Rippenfläche der Bewehrung und der Betonfestigkeit sowohl auf die Verbundspannungen als auch auf die zugehörigen Schlupfwerte berücksichtigt. Über einen zusätzlichen Datensatz zum Einfluss der Verbundlänge im Ausziehversuch konnte ebenfalls die Abhängigkeit zwischen den mittleren Verbundspannungen, den zugehörigen Schlupfwerten und der Verbundlänge spezifiziert werden. Somit ist eine Übertragbarkeit der Ergebnisse von Ausziehversuchen mit kurzen Verbundlängen auf eine reale Einbettungslänge im Bauteil möglich. Für die Bemessung von Stahlbetonkonstruktionen in den Grenzzuständen der Tragfähigkeit und der Gebrauchstauglichkeit erfolgt die Ableitung geeigneter Verformungskriterien für die Relativverschiebung zwischen Betonstahl und Beton und deren Verifizierung an Versuchsdaten aus der Literatur. Die aufgestellten Verformungskriterien in Abhängigkeit der Stahlspannung erlauben eine direkte Ermittlung bemessungsrelevanter Verbundspannungen anhand experimenteller Ausziehversuche. Die Berücksichtigung einer Querzugbelastung ist dabei in allen vorgestellten Berechnungsansätzen ebenfalls möglich. / Reinforced concrete as composite material is characterised by an effective interaction of its individual components reinforcing steel and concrete. This only can be assured by adequate bond conditions between these two materials. The bond quality is influenced by a wide range of parameters, amongst others including the rib geometry of the bar, the concrete strength and the confining action by the surrounding concrete or transverse reinforcement. Moreover loads, which act transverse to the reinforcing bar, can influence the bond mechanism and the bond failure mode significantly. Reinforced concrete structures, such as containment walls or two-way slabs, are often exposed to multiaxial loading conditions. In case of biaxial tensile stresses, reinforcement and surrounding concrete are loaded in tension in longitudinal as well as in transverse direction. An extensive experimental program was carried out in order to investigate the bond behaviour between reinforcing steel and normal strength concrete due to transverse tension. Cubic-shaped pullout specimens with a short bond length were used. The transverse tension level remained always below the cracking stress of concrete, meaning that no crack occurred along the pullout bar. The test program contained the variation of the transverse tension level, the concrete strength, the bar diameter and the concrete cover. From the test results no systematic influence of the transverse tension level on the shape of the bond stress-slip-relationship can be detected. The bond failure mode is significantly influenced by transverse tension, which promotes splitting failure. The higher the transverse tension level, even for high concrete covers, splitting failure occurs instead of pulling out the bar. From the test results, a failure criterion depending on the concrete cover and the transverse tension level could be determined, which indicates the failure mode and corresponding bond stress. For this purpose, the influence of the specimen geometry on the test results was considered, which results in a failure criterion that is also valid for real embedment lengths of the reinforcement. Furthermore, a bond model for short bond lengths has been developed, based on the test results and a dataset from literature. The model considers the influence of the related rib area of the reinforcing bar and the concrete strength on the bond stresses as well as on the corresponding slip values. By an additional dataset concerning the influence of bond length in pullout tests, the bond stresses and corresponding slip values could be specified as a function of the bond length. Therefore, the test results of pullout test with short bond lengths are transferable to real embedment lengths in structural elements. For the structural design of reinforced concrete elements in the ultimate and serviceability limit states, appli\\-cable deformation criterions concerning the relative displacement between reinforcing steel and concrete has been derived and verified by test data from literature. By means of the developed deformations criterions dependent on the steel stress, design bond stresses can be determined directly from experimental pullout tests. The consideration of transverse tensile loads is also possible for all presented design formulas.

Die sichere Einleitung und Übertragung der wirkenden Kräfte ist Bedingung für die Funktionsfähigkeit und die vollständige Ausnutzung der Tragfähigkeit von Textilbetonbauteilen und -verstärkungsschichten. So kann es bei ungünstiger Konfiguration und Anordnung der Einzelkomponenten des Verbundbaustoffes zur Ausbildung einer Vielzahl verschiedener Verbundversagensformen kommen. Diese umfassen neben der Bildung von verbundschädigenden Delaminations- und Spaltrissen lokale Abplatzungen der Betondeckung oder einen vorzeitigen Auszug der Garne aus dem Beton. Besonders beansprucht sind in diesem Zusammenhang die bei einer Anwendung von Textilbeton erforderlichen Endverankerungs- und Stoßbereiche der textilen Bewehrungen. Zur sicheren Ausbildung und Bemessung dieser wichtigen Detailpunkte liegen jedoch momentan noch keine umfassenden und zusammenhängenden Untersuchungen vor. Hauptziel der vorliegenden Dissertation war daher eine systematische Erforschung und Beschreibung des Tragverhaltens von Textilbeton in Endverankerungs- und Übergreifungsbereichen. Eine funktionierende und schädigungsfreie Verbundkraftübertragung bildet die Grundlage für die sichere Lasteinleitung und -übertragung. Daher wurden im ersten Teil der Arbeit ausführliche Untersuchungen zur Charakterisierung der zwischen Bewehrungstextil und Feinbetonmatrix wirkenden Kräfte und -mechanismen durchgeführt. Nach der Entwicklung eines geeigneten Versuchsaufbaus erfolgten umfangreiche Parametervariationen zur experimentellen Überprüfung des textilspezifischen Verbundverhaltens. Den Schwerpunkt der Untersuchungen bildete die Identifikation und Bewertung der aus verschiedenen Verarbeitungsparametern der textilen Bewehrungen resultierenden Verbundeinflüsse. Die Versuchsergebnisse ermöglichen die Bestimmung der zugehörigen Verbundspannungs-Schlupf-Beziehungen (VSB) mithilfe eines erarbeiteten Modellierungsverfahrens. Die so ermittelten Verbundkennwerte bilden die Grundlage für die weiteren rechnerischen Untersuchungen. Im zweiten Teil der Arbeit erfolgten Forschungen zum Tragverhalten von Endverankerungsbereichen. Hierbei stand der im Regelfall bemessungsrelevante Grenzzustand eines vorzeitigen Auszuges der Textilien aus der Betonmatrix im Mittelpunkt. Die Arbeiten umfassten experimentelle und theoretische Untersuchungen zur Beschreibung der Kraftübertragung. Aufbauend auf die ermittelten Verbundkennwerte wird ein unabhängiger analytischer Auswertealgorithmus zur Beschreibung des Verbundtragverhaltens in Endverankerungsbereichen dargestellt. Dieser ermöglicht eine detaillierte rechnerische Bestimmung der erforderlichen Endverankerungslängen von Textilbeton in Abhängigkeit konkreter bzw. untersuchter Bewehrungstextilien. Den dritten Forschungsschwerpunkt bildeten Untersuchungen zum Tragverhalten von Übergreifungsstößen in Textilbetonbauteilen. Mithilfe von umfassenden experimentellen und theoretischen Analysen an unterschiedlich konfigurierten und bewehrten Textilbetonen konnten die maßgebenden Versagensmechanismen untersucht und grundlegende Vorgaben für die Bemessung und Ausführung der Übergreifungsbereiche abgeleitet werden. Die gewonnenen Erkenntnisse wurden anhand von großformatigen Bauteilversuchen mit entsprechend konstruierten Übergreifungsstößen bestätigt. Zum Abschluss wird ein vereinfachtes Ingenieurmodell vorgestellt. Dieses erlaubt eine allgemeingültige und hinreichend genaue Bemessung der untersuchten Detailpunkte unter Beachtung der maßgebenden Grenzzustände. / The safe introduction and transmission of forces is a requirement for the workability as well as the possibility to make full use of the load bearing capacities of components and strengthening layers made of textile reinforced concrete. Accordingly, an unfavourable configuration and arrangement of the composite material’s individual components can lead to various modes of bond failure. These can result from the formation of bond damaging delamination cracks and longitudinal matrix splitting, local spalling of the concrete layer in the outer reinforcement layers or early yarn pull-out from the concrete. In this context, the areas of end anchorage and lap joints of the textile reinforcement, which cannot be avoided when using textile reinforced concrete, are particularly prone to failure. However, no comprehensive and coherent investigations regarding the safe configuration and dimensioning of these essential details are available yet. Consequently, systematic research into textile reinforced concrete’s load-bearing behaviour in the areas of end anchorage and lap joints and the subsequent description was the main goal of this dissertation. A working and damage-free transmission of bond force is the basis for a faultless load transmission and introduction. As a result, extensive tests concerning the characterization of the mechanisms and forces acting between reinforcing textile and fine grained concrete matrix were carried out as the first part of the investigations. After an appropriate test setup had been developed, a great variety of parameters was applied to experimentally examine the bond behaviour specific to the textile. The determination of the influencing factors resulting from various parameters in the textile reinforcement’s processing was a focus in the research. Based on a specifically developed modelling technique, the test results could be used to calculate the corresponding bond stress-slip-relation. The bond parameters, which were determined like this, served as the basis for the following calculations. The second part of the investigations was concerned with the load-bearing behaviour in end anchorage areas. In this case, the limit state of a yarn pull-out from the concrete matrix, which is usually essential for the dimensioning, was at the centre of attention. The investigations encompassed experimental and theoretical tests regarding the description of the force transmission. Based on the determined compound parameters, an independent analytic evaluation algorithm, which served to describe the load carrying behaviour of the bond in the end anchorage area, was presented. Through this algorithm, the detailed calculation of the required end anchorage lengths of textile reinforced concrete depending on the specific reinforcement textile was possible. The third research focus was on tests regarding the load-bearing behaviour of lap joints in textile reinforced concrete components. With the help of comprehensive experimental and theoretical analyses of variously configured and reinforced textile reinforced concretes, the decisive failure mechanisms were examined. Furthermore, fundamental demands for the dimensioning and execution of the lap joint areas could be derived. The findings were confirmed through tests on large-sized building components with corresponding lap joints. At the end of the investigations, a simplified engineering model is presented. This model makes a universally valid and exact dimensioning of the examined details possible while also paying attention to the decisive limit states.