Fundação de Amparo a Pesquisa do Estado de Minas Gerais / This work is dedicated to the development of a strategy for numerical-computational modeling and experimental verification of the self-heating phenomenon in viscoelastic materials with emphasis on the thermal runaway phenomenon taking into account the combined effects of dynamic loads and static preloads. The methodology of modeling by finite element allows us to consider the influence of frequency, temperature and static preload on the self-heating phenomenon of the linear viscoelastic materials. For this purpose, modifications are made that allow thermomechanical analysis of more complex viscoelastic structures, in addition the evaluation of introducing metal inserts in bulk material for reducing effects of self-heating. The validation of the proposed model and the identification of the physical parameters of thermal efficiency and heat transfer by natural convection, initially unknown, are obtained by comparison of the results of numerical simulations with the corresponding obtained through experimental tests for a specimen formed by a translational viscoelastic joint. The curve-fitting procedure is formulated as an inverse optimization problem through use of the Firefly Algorithm for minimizing the objective function defined as the square difference between the temperatures obtained from the simulations and the corresponding generated by the tests for each time instant. The accuracy and limitations of the model are evaluated by comparing the experimental and simulated temperature profile, allowing to verify the numerical evidence and the qualitative consistence of the results obtained with reported in the literature for the thermal runaway phenomenon for simple devices without effect preload. / Este trabalho é dedicado ao desenvolvimento de uma estratégia de modelagem numéricocomputacional e verificação experimental do fenômeno do autoaquecimento de materiais viscoelásticos com ênfase no fenômeno da fuga térmica levando-se em conta os efeitos combinados de cargas dinâmicas e pré-cargas estáticas. A metodologia de modelagem por elementos finitos permite considerar a influência da frequência, da temperatura e da pré-carga estática no fenômeno do autoaquecimento de materiais viscoelástico lineares. Para tanto, são feitas modificações que permitem a análise termomecânica de estruturas viscoelásticas mais complexas, além da avaliação da introdução de insertos metálicos no volume do material para a redução dos efeitos do autoaquecimento. A validação do modelo proposto e a identificação dos parâmetros físicos de rendimento térmico e de transferência de calor por convecção natural incialmente desconhecidos, são obtidos através da confrontação dos resultados das simulações numéricas com os correspondentes obtidos via ensaios experimentais para um corpo de prova formado por uma junta viscoelástica translacional. O procedimento de ajuste de curvas é formulado como um problema inverso de otimização via emprego da técnica Colônia de Vagalumes para a minimização da função objetivo definida como sendo a diferença quadrática entre as temperaturas obtidas das simulações e as correspondentes geradas pelos ensaios para cada instante de tempo. A precisão e as limitações do modelo são avaliadas pela comparação dos perfis simulados e experimentais de temperatura, possibilitando confirmar as evidências numéricas e a consistência qualitativa dos resultados obtidos com o reportado na literatura para o fenômeno da fuga térmica para dispositivos mais simples e sem o efeito da pré-carga. / Mestre em Engenharia Mecânica

This thesis discusses the types of bridge expansion joints certified for use in the Czech Republic and their disorders. The first part was a theoretical evaluation of expansion joint failures. The second part focused on clarifying the failure of anchor bolts at the cantilever expansion joint. On the basis of determining the cause was then designed a method for determining the durability of expansion joints. Prognosis life cycles corresponds records according to administrator- repair works.

This thesis addresses the static security chapel in Medlice. The chapel is a single-Gothic style. The other two dimensions 8x14 m chapels are part of the chapel tower is 20 m high with dimensions of 2,6 x2, 6 m Chapel was built in 1901. The truss chapel was damaged by pests, and therefore, a need to examine and exchange truss. On this occasion, establish a reinforced concrete ring that object until now lacked. In bearing walls of the chapel are visible cracks and occurs because the horizontal bracing object using a technology called monostrands.

Orientador: Francisco José Teixeira Neto / Resumo: Objetivo: Comparar a acurácia diagnóstica da variação da pressão de pulso (VPP), variação do volume sistólico mensurada através do análise de contorno de pulso (VVSACP), índice de variabilidade pletismográfica (IVP), pressão venosa central (PVC) e índice do volume diastólico final global mensurado pela técnica de termodiluição transpulmonar (GEDVITDTP) para predizer a fluido-responsividade em cães. Animais: Quarenta cadelas saudáveis (13,8–26,8 kg) submetidas a ovário-salpingo-histerectomia. Métodos: A anestesia foi mantida com isoflurano sob ventilação mecânica com volume controlado (volume corrente 12 mL/kg, pausa inspiratória 40%, relação inspiração/expiração: 1:1,5). O débito cardíaco e o volume sistólico foram obtidos pela técnica de termodiluição transpulmonar através de um cateter inserido na artéria femoral. A fluido-responsividade (FR) foi avaliada por uma prova de carga (solução de Ringer com lactato, 20 mL/kg durante 15 minutos), administrada uma vez (n = 21) ou duas vezes (n = 18) antes da cirurgia. Respondedores a volume foram definidos como indivíduos onde o VS mensurado pela técnica de termodiluição transpulmonar, elevou-se acima de 15% após a última prova de carga. Resultados: Dos 39 animais incluídos no estudo, 21 cães foram classificados como respondedores e 18 não respondedores ao último desafio volêmico. As áreas sob as curvas de características de operação do receptor (AUROC) foram de 0,976, 0,906, 0,868 e 0,821 para VPP, IVP, PVC e VVSACP, respectivament... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Objective: To compare the diagnostic accuracy of pulse pressure variation (PPV), stroke volume variation from pulse contour analysis (SVVPCA), plethysmographic variability index (PVI), central venous pressure (CVP) and global end-diastolic volume index measured by transpulmonary thermodilution (GEDVITPTD) to predict fluid responsiveness (FR) in dogs. Animals: A group of 40 bitches (13.8–26.8 kg) undergoing ovariohysterectomy. Methods: Anesthesia was maintained with isoflurane under volume-controlled ventilation (tidal volume 12 mL/kg; inspiratory pause during 40% of inspiratory time; inspiration: expiration ratio 1:1.5). Transpulmonary thermodilution cardiac output was recorded through a femoral artery catheter. FR was evaluated by a fluid challenge (lactated Ringer's, 20 mL kg over 15 minutes) administered once (n = 21) or twice (n = 18) before surgery. Individuals were responders if stroke volume index measured by transpulmonary thermodilution increased >15% after the last fluid challenge. Results: Of the 39 animals studied, 21 were responders and 18 were nonresponders. Area under the receiver operating characteristics curve (AUROC) was 0.976, 0.906, 0.868 and 0.821 for PPV, PVI, CVP and SVVPCA, respectively (p < 0.0001 from AUROC = 0.5). GEDVITPTD failed to predict FR (AUROC: 0.660, p = 0.078). Best cut-off thresholds discriminating responders and nonresponders, with respective zones of diagnostic uncertainty (gray zones) were: PPV >16% (15–16%), PVI >11% (10–13%), SVVPCA ... (Complete abstract click electronic access below) / Doutor

In this thesis an investigation of the effect of preload on the fatigue behaviour of additively manufactured (AM) 316L stainless steel parts with less than 5 % porosity, for both horizontal and vertical build direction, is presented. The specimens used were manufactured by selective laser melting (SLM) and cut by EDM. Preloads at two different magnitudes were used, below and above the yield strength of the material, and fatigue tests were performed on the specimens with and without the preloads. In addition, microstructural analysis was carried out in order to illustrate/quantify the defects and to realize the corresponding effect of the preload by use of white light interferometry (WLI), SEM and FEM modeling. It was found that the fatigue life and the fatigue limit clearly increase with increasing the preloads in both build directions, although the preload significance might be varied for different directions. This was attributed to the imposed compressive residual stresses and blunting of sharp defects after preloading. / I detta examensarbete presenteras en undersökning på effekten av förbelastning på utmattningsbeteendet hos additivt tillverkade (AM) komponenter av 316L rostfritt stål med mindre än 5 % porositet, för både horisontell och vertikal byggriktning. Provstavarana tillverkades genom selektiv lasersmältning (SLM) och skars ut med trådgnist (EDM). Förspänningar i två olika storlekar användes, under och över materialets sträckgräns, och utmattningstester utfördes på provstavarna med och utan förspänningarna. Dessutom genomfördes mikrostrukturella analyser för att illustrera / kvantifiera defekterna och effekten av förspänningen med användning av vitt ljusinterferometri (WLI), SEM och FEM-modellering. Det visade sig att utmattningslivslängden och utmattningsgränsen tydligt ökar med ökad förspänning i båda byggriktningarna, även om förspänningens betydelse kan variera för olika riktningar. Denna positiva effekt på utmattningen kommer från de kompressiva restspänningarna och avstumpningen av skarpa defekter som uppstår efter förbelastningen.

Ausgangspunkt der hier vorgestellten Entwicklungen ist eine am ICM – Institut Chemnitzer Maschinen- und Anlagenbau e.V. entwickelte adaptronische Werkzeugmaschinen-Hauptspindel zur variablen Einstellung der Lagervorspannkräfte. Diese neuartige Werkzeugmaschinenspindel bietet Anwendungspotentiale in den Bereichen: verbessertes Hochdrehverhalten, erhöhte Flexibilität des Bearbeitungsspektrums, Lebensdauererhöhung der Wälzlager durch verbessertes Bohr-Roll-Verhältnis sowie einer optimierten Spindeldynamik durch gezielte Verschiebung der Eigenfrequenzen. Ziel war die Entwicklung einer möglichst dynamischen und genauen Ansteuerung des in der Hauptspindel enthaltenen hydraulischen Vorspannelementes. Dieser Beitrag fasst das Vorgehen und die bisherigen Ergebnisse zusammen. Auf die Eigenentwicklung eines hydraulischen Aktuators sollte verzichtet werden, sodass die Ansteuerung über ein direktgesteuertes Regelventil erfolgt. Mit einer einfachen Druckregelung mit PID-Regler konnten nur unzureichende Ergebnisse hinsichtlich Dynamik und Regelkreisstabilität erzielt werden. Hinzu kommt die geringe Genauigkeit der Krafteinstellung bei Anwendung einer einfachen Druckregelung. Zur Verbesserung der Ansteuerungsdynamik und -genauigkeit des Vorspannelementes sollten erweiterte Regelungsstrukturen zur Anwendung kommen. Im Projekt wurde hierzu ein modellbasierter Regler entwickelt und in einer dem Experiment vorgelagerten Untersuchung an einem Systemsimulationsmodell getestet und optimiert. Ausgangspunkt für die simulationsgestützte Reglerauslegung war die Entwicklung eines Regelstreckenmodells in SimulationX. Die Modellentwicklung umfasste den Vergleich zweier grundlegender Modellierungsansätze, eines bidirektionalen Modells mit einem linearen Signalflussmodell hinsichtlich Modellgenauigkeit und Rechenperformance. Zur Untersuchung der Reglerfunktionalität sowie zur Optimierung der Reglerparameter wurde die in SimulationX vorhandene COM-Schnittstelle genutzt und eine vereinfachte Optimierungsfunktion in Matlab umgesetzt. Für die experimentelle Validierung des Ansteuerungssystems wurde die entwickelte modellbasierte Reglervorsteuerung in der Programmierumgebung LabView umgesetzt. Erste Tests erfolgten zunächst an der stehenden Hauptspindel. Diese zeigten ein sehr dynamisches und stabiles Regelungsverhalten, sodass neben einfachen Sprungvorhaben auch Trajektorienvorgaben mit hoher Dynamik geregelt werden können. Es konnte eine deutliche Verbesserung gegenüber der zu Beginn vorhandenen einfachen Druckregelung erzielt werden. Umfangreichere experimentelle Untersuchungen an der drehenden Spindel für unterschiedliche Regelungs- und Bearbeitungsszenarien sollen in Zukunft durchgeführt werden. Dabei stehen vor allem die Verkürzung der Hochdrehzeiten für Bearbeitungsprozesse mit geringer Lagervorspannung sowie die anwendungsspezifische Optimierung der Spindeldynamik durch Eigenfrequenzverschiebungen im Vordergrund. / The starting point of the developments presented here is an adaptronic machine tool main spindle developed at the ICM - Institute Chemnitz Machine and Plant Construction e.V. for variable adjustment of the bearing preload forces. This new type of machine tool spindle offers application potential in the areas of: improved high-speed behavior, increased flexibility of the machining spectrum, increased service life of the roller bearings through improved drilling-rolling ratio and optimized spindle dynamics through targeted shifting of the natural frequencies. The aim was to develop the most dynamic and precise control possible for the hydraulic pretensioning element contained in the main spindle. This article summarizes the procedure and the results so far. The in-house development of a hydraulic actuator should be avoided, so that the control takes place via a directly controlled control valve. With a simple pressure control with a PID controller, only insufficient results could be achieved in terms of dynamics and control loop stability. Added to this is the low accuracy of the force setting when using a simple pressure control. Extended control structures should be used to improve the control dynamics and accuracy of the preload element. For this purpose, a model-based controller was developed in the project and tested and optimized on a system simulation model in an investigation prior to the experiment. The starting point for the simulation-based controller design was the development of a controlled system model in SimulationX. The model development included the comparison of two basic modeling approaches, a bidirectional model with a linear signal flow model in terms of model accuracy and computational performance. The COM interface available in SimulationX was used to examine the controller functionality and to optimize the controller parameters, and a simplified optimization function was implemented in Matlab. For the experimental validation of the control system, the developed model-based controller pre-control was implemented in the LabView programming environment. The first tests were initially carried out on the stationary main spindle. These showed a very dynamic and stable control behavior, so that in addition to simple jump projects, trajectory specifications can also be controlled with high dynamics. A clear improvement could be achieved compared to the simple pressure control that was available at the beginning. More extensive experimental investigations on the rotating spindle for different control and processing scenarios are to be carried out in the future. The main focus here is on reducing the ramp-up times for machining processes with low bearing preload and the application-specific optimization of the spindle dynamics through natural frequency shifts.

Detta examensarbete behandlar bullerskärmar för järnvägen längs Mälarbanan. Det nuvarande utförandet av konstruktionen har visat sig få problem med utmattning av de skruvförband som förbinder bullerskärmen med grundkonstruktionen. Konstruktionen uppfyller inte den tilltänkta livslängden. Examensarbetet föreslår förbättringar av konstruktionen. Denna kan enkelt modifieras, så att skruvförbanden blir förspända vilket minskar lastamplituden. Europeiska regelverk gällande stålkonstruktioner beaktas. Det förnämliga är att de inte fordrar några större eller kostsammare förändraringar av dagens utförande. Två lösningsförslag föreligger och presenteras i rapporten / This thesis project is about railroad noise barriers along the Mälarbanan. The current construction design has been found to have fatigue problems related to the threaded rods connecting the noise screen to the ground structure. This results in the barrier not sustaining the intended life expectancy. The aim of this thesis project has been to improve the current construction design by suggesting solutions enabling the construction to withstand the dynamic loads. The goal of this project has been achieved through reviews of the current construction, previous consulting reports and by taking in consideration the European standards for steel constructions along with Trafikverkets rules and regulations. This has resulted in two solution proposals, for current and future constructions, without the need for major design changes.

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Die Auswahl einer zweckmäßigen Verbindungstechnik hat großen Einfluss auf die Kosten für die Herstellung und Wartung von Gütern. Das mechanische Verbinden von Bauteilen mit Schließringbolzen gehört zum umformtechnischen Fügen. Damit werden kostengünstig unlösbare und mechanisch hoch beanspruchbare, punktförmige Verbindungen erzeugt. Die vorliegende Arbeit hatte das Ziel, in umfassender Form den Nachweis zu erbringen, dass mit Schließringbolzensystemen ohne Sollbruchstelle wartungsfreie Verbindungen hergestellt werden können. Diese Wartungsfreiheit bezieht sich auf den Erhalt der mechanischen Eigenschaften der Verbindung und des Korrosionsschutzes bis zur beabsichtigten Grenznutzungsdauer. Aus einer Analyse des Standes der Technik wurde der Forschungsbedarf hinsichtlich der Wartungsfreiheit von Schließringbolzenverbindungen aus mechanischer und korrosiver Sicht abgeleitet. In einem mehrstufigen Prüfprogramm, unterteilt nach Anwendungen im Nutzfahrzeugbau und Stahlbau, wurde nach maschinenbaulichen und stahlbaulichen Konzepten die mechanische Leistungsfähigkeit der Verbindungen untersucht. Die Forschungsergebnisse aus diesem Programm und der Test neu entwickelter Beschichtungssysteme für die Bolzen und die Schließringe bestätigten die Eingangsthese über die Wartungsfreiheit. Metallografische Analysen und FEM Rechnungen ergänzen die Arbeit. Sie ist in sechs Abschnitte unterteilt und enthält 135 Abbildungen, 25 Tabellen, 3 Anlagen. Es wurden 118 Literaturquellen berücksichtigt. Mit der Arbeit steht dem Ingenieur ein umfangreiches Auskunftsmaterial zum Vergleich von Schließringbolzenverbindungen mit anderen Fügeverfahren, besonders jedoch zur Verschraubung zur Verfügung. Die durchgeführten Untersuchungen und Aussagen sollten in zukünftiger Forschung zu einem ganzheitlichen Konzept für die rechnerische Auslegung und Dimensionierung von Schließringbolzenverbindungen nach dem Vorbild der VDI 2230 und der EN 1993 weitergeführt werden.

The design of a bolted joint shall consider several factors such as material and heat treatment of the bolt (defined by the class of the bolt), stiffness of the parts being assembled (stiffness of the union), dimensions of the bolt, among others. In our study we used bolts M6x1, class 8.8, with three different lengths: 40 mm, 60 mm and 80 mm. The purpose of this study is to verify the relationship between the length of the bolt and the fatigue limit of the bolted joints, subjected to fluctuating cyclic loading of tension. The results indicated that the greater the length of the bolt, the larger the fatigue limit. An analytical study was also evaluated on the relationship between the cyclic stress amplitude and the mean stress experienced by the bolts with 40 mm of length. The results were compared with the bolt fatigue diagram of the BURGUETE and PATTERSON (1995). Correction factors were proposed for the relationship between cyclic stress amplitude. The adapted model from LEHNHOFF and WISTEHUFF (1996) for M6 bolts was the one whose results were the closest to estimated. / O projeto de uma união parafusada deve considerar diversos fatores tais como material e tratamento térmico do parafuso (definidos pela classe do parafuso), rigidez das peças que estão sendo montadas (rigidez da união), dimensões do parafuso, entre outros. Em nosso estudo utilizamos parafusos M6x1, classe 8.8, com três comprimentos distintos: 40 mm, 60 mm e 80 mm. A proposta deste estudo é verificar a relação do comprimento do parafuso com o limite de fadiga de uniões parafusadas submetidas a carregamentos cíclicos de tração. Os resultados indicaram que quanto maior o comprimento do parafuso, maior é o limite de fadiga. Foi realizado ainda um estudo analítico da relação entre a amplitude de tensão e a tensão média suportada pelos parafusos de 40 mm de comprimento. Os resultados foram comparados com o diagrama de BURGUETE e PATTERSON (1995). Foram propostos coeficientes de correção para a relação entre as amplitudes de tensão. O modelo de rigidez adaptado de LEHNHOFF e WISTEHUFF (1996) para parafusos M6 foi o que apresentou resultado mais próximo aos estimados.