Im Rahmen der Arbeit wurde das Potential von Magnesium für den Einsatz im Fahrwerk eines Automobils, am Beispiel der Querbrücke des Hinterachsträgers, ermittelt. Verschiedene Mg-Legierungen wurden im konventionellen und vakuumunterstützen Druckguss vergossen und der Al-Legierung vergleichend gegenübergestellt. Es wurden in einem ersten Schritt statische und zyklische Werkstoffkennwerte sowie Materialmodelle erforscht und bewertet. Verschiedene Lastfälle im Standard- und Sonderfahrbetrieb wurden durch statische und zyklische Betriebsfestigkeitssimulationen abgesichert. Konstruktive Bauteiloptimierungen waren notwendig um den Werkstoff Magnesium an die Anforderungen der Querbrücke anzupassen. Äußere Umwelteinflüsse im Fahrbetrieb machten ein Korrosionsschutzkonzept für die Querbrücke aus Magnesium notwendig. Untersucht wurden dabei verschiedene Maßnahmen zur Vermeidung von Kontakt- und Oberflächenkorrosion. Grundsätzlich scheint der Einsatz von Magnesium im Fahrwerk im Bereich mittlerer Betriebsbelastungen denkbar.

In recent years a strong interest has been expressed to produce lighter structures.One possible solution to reduce the weight is to utilize high strength steels and use welding as the joining method. Many components experience fatigue loadingduring all or part of their life time and welded connections are often the prime location of fatigue failure. This becomes more critical in welded high strength steels as fatigue strength of welds does not increase by increasing the steel strength. A possible solution to overcome this issue is to use fatigue improvement methods.The main objectives of this project are, therefore, to increase understanding of the factors that control fatigue life and to investigate how the fatigue strength improvement methods; high frequency mechanical impact (HFMI) treatment and use of Low Transformation Temperature (LTT) consumables will affect fatigue properties of welds in high strength steels. In this regard, Gas Metal Arc Welding(GMAW) was used to produce butt and fillet welds using LTT or conventional fillers in steels with yield strengths ranging from 650-1021 MPa and T-joint weldsin a steel with 1300 MPa yield strength. The effect of HFMI on fatigue strength of the welds in 1300 MPa yield strength steels was also investigated. Butt and fillet welds in 650-1021 MPa steels were fatigue tested under constant amplitude tensile loading with a stress ratio of 0.1 while T-joints were fatigue tested under constant amplitude fully reversed bending load with a stress ratio of -1. The nominal stress approach was used for fatigue strength evaluation of butt and fillet welds whereas the effective notch stress approach was used in case of T-joints. Relative effectsof the main parameters such as residual stress and weld toe geometry influencing fatigue strength of welds were evaluated. Residual stresses were measured using X-ray diffraction for as-welded and HFMI treated welds. Neutron diffraction was additionally used to investigate the near surface residual stress distribution in 1300 MPa LTT welds.Results showed that use of LTT consumables increased fatigue strength of welds in steels with yield strengths ranging from 650-1021 MPa. For butt welds, the vii characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to46% higher when compared to corresponding welds made with conventional fillermaterials. In fillet welds, a maximum improvement of 132% was achieved when using LTT wires. The increase in fatigue strength was attributed to the lower tensile residual stresses or even compressive stresses produced close to the weldtoe in LTT welds. Weld metals with martensite transformation start temperatures around 200 °C produced the highest fatigue strength. In 1300 MPa yield strength steel, similar FAT of 287 MPa was observed for LTT welds and 306 MPa for conventional welds, both much higher than the IIW FATvalue of 225 MPa. The relative transformation temperatures of the base and weldmetals, specimen geometry and loading type are possible reasons why the fatigue strength was not improved by use of LTT wires. Neutron diffraction showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It was additionally found that there arevery steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe. Due to difficulties to accurately measure residual stresses locally at the weld toe most often in the literature and recommendations residual stresses a few millimetre away from the weld toe are related to fatigue properties. However, this research shows that caution must be used when relating these to fatigue strength, in particular for LTT welds, as stress in the base materiala few millimetre from the weld toe can be very different from the stress locally at the weld toe.HFMI increased the mean fatigue strength of conventional welds in 1300 MPa steels about 26% and of LTT welds by 13%. It increased the weld toe radius slightly but produced a more uniform geometry along the treated weld toes. Large compressive residual stresses, especially in the longitudinal direction, were introduced adjacent to the weld toe for both LTT and conventional treated welds. It was concluded that the increase in fatigue strength by HFMI treatment is due to the combined effect of weld toe geometry modification, increase in surface hardness and introduction of compressive residual stresses in the treated region.It was concluded that the residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welds. This is based on the observation that a moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm, in fillet welds. Also, a higher fatigue strength was observed for HFMI treated conventional welds compared to as welded samples having similar weld toe radii but with different residual stresses.

This thesis is focused on the issue of computational modeling of soil harvesting while using the compact excavator from the company DOOSAN BOBCAT EMEA s.r.o.. The solution consists in creating two computational models in Rocky DEM and Ansys Mechanical. Rocky DEM software is used to solve the disconnection of soil by excavator components using the discrete element method. The outcome includes courses of forces and moments during the particular time of the individual joints of the model that was used. The obtained courses are then applied as an external load to the joint of a selected structural part of the analyzed model using a kinematic model in ANSYS Mechanical. The kinematic model consists of simplified geometry models of individual parts of the excavator arm, and a more detailed geometry model of the analyzed part of the arm. All the parts are connected to each other by rotational bonds representing joints. A static structural analysis of the mechanical stress is performed in ANSYS Mechanical for the prepared model during the simulated process. Finally, the selected structural part is assessed with respect to the elastic limit and fatigue strength.

The increasing demands for lightweight designs with high strength call for improved manufacturing processes regarding heat treatment of steel. The manufacturing process has considerable potential to improve the mechanical performance and to obtain more reliable results with less variation. The goal of this thesis is to establish new knowledge regarding improved manufacturing processes in industrial heat treatment applications. Three research questions with associated hypotheses are formulated. Process experiments, evaluation of the mechanical performance, and modelling of the fatigue behaviour assist in answering the questions. The gas quenching procedure following low-pressure carburising differs from the conventional procedure of gas carburising and oil quenching. It is shown that the introduction of a holding time during the low-temperature part of the quench has a positive effect on mechanical properties, with some 20 percent increase in fatigue strength. This is attributed to increased compressive surface residual stress and stabilisation of austenite. Tempering is a common manufacturing process step following hardening in order to increase the toughness of the steel. However, the research shows that the higher hardness from eliminating tempering from the manufacturing process is beneficial for contact fatigue resistance. The untempered steel showed not only less contact fatigue damage but also a different contact fatigue mechanism. Straightening of elongated components is made after heat treatment in order to compensate for distortions. The research shows that straightening of induction hardened shafts may lead to lowering of the fatigue strength of up to 20 percent. A fracture mechanics based model is developed to estimate the effects of straightening on fatigue strength. / Ökande krav på höghållfasta lättviktskonstruktioner kräver förbättrade tillverkningsprocesser för värmebehandling av stål. Det finns stor potential att förbättra mekanisk prestanda och att erhålla mer tillförlitliga resultat med mindre variation genom att förbättra tillverkningsprocessen. Målet med denna avhandling är att etablera ny kunskap kring tillverkningsprocesser inom industriella värmebehandlingsapplikationer. Tre forskningsfrågor med tillhörande hypoteser formuleras. Processexperiment, utvärdering av mekanisk hållfasthet och modellering av utmattningsbeteende bygger upp besvarandet av frågorna. Gaskylning som följer lågtrycksuppkolning skiljer sig från det konventionella förfarandet med gasuppkolning och släckning i olja. Resultaten visar att en hålltid i den nedre delen av kylningsförloppet har positiv inverkan på utmattningshållfastheten. Orsaken till förbättringen hänförs till ökade tryckrestspänningar samt stabilisering av austenit. Anlöpning är en vanlig tillverkningsprocess som efterföljer härdning för att öka stålets seghet. Forskningen visar däremot att den högre hårdheten för oanlöpt stål är fördelaktig för motstånd mot kontaktutmattning. Oanlöpt stål visade mindre mängd kontaktutmattningsskador och även en annan skademekanism. Riktning av långa komponenter görs efter värmebehandling för att kompensera för de formförändringar som uppstår. Forskningen visar att riktning av induktionshärdade axlar kan leda till sänkning av utmattningshållfastheten med upp till 20 procent. En brottmekanisk modell som uppskattar effekten av riktning på utmattningshållfasthet presenteras. / <p>QC 20150410</p>

L’industrie pétrolière s’intéresse aujourd’hui à la possibilité de remplacer certaines brasures par des joints adhésifs rendus conducteurs par leur fort taux de charges conductrices dans les outils électroniques. Ces outils évoluent aujourd’hui à des hauts niveaux de température et de pression pendant leur vie en service. L’utilisation de joints adhésifs pose donc automatiquement la question de leur fiabilité à long terme. L’étude de leur tenue en fatigue, et de l’influence du vieillissement sur cette tenue en fatigue devient nécessaire pour le déploiement final de ces joints. Cette thèse se propose de répondre à une double question : la prédiction de la durée de vie de deux colles commerciales dans les outils électroniques et l’influence du vieillissement de ces colles sur cette prédiction. Deux vieillissements différents ont été mis en œuvre : un vieillissement à l’air libre et un vieillissement inerte (sous argon) confiné.Dans un premier temps, une caractérisation expérimentale du comportement viscoélastique des colles a été menée. Elle met en particulier l’accent sur les non-linéarités induites par les deux paramètres de chargements retenus que sont le cisaillement et la pression hydrostatique.Dans un deuxième temps, une étude plus fine de la microstructure a été effectuée numériquement. Une série d’hypothèses de modélisation a été faite. Les résultats de ces calculs - plutôt qualitatifs - permettent de dégager les tendances sur l’influence de la présence des charges conductrices sur la réponse macroscopique du joint adhésif.Enfin, la tenue en fatigue des joints et sa dépendance à leur vieillissement a été abordée expérimentalement. L’influence de l’atmosphère et du confinement pendant le vieillissement sur l’évolution de la tenue en fatigue a été mise en évidence pour les deux colles étudiées dans cette thèse. Les résultats obtenus ont permis de proposer des lois de fatigue dont certains paramètres dépendent du vieillissement. / The substitution of soldering by electrically conductive adhesive bonding in electronic assemblies is of growing interest in the oil-and-gas industry. These electronic assemblies should nowadays work at high temperature and pressure levels during their service lives. The question of the long-term reliability of adhesive bonding becomes in this context a critical issue. The study of the fatigue strength of adhesive joints as well as the influence of ageing on this strength is therefore crucial for the final deployment of adhesive bonding. This work aims at addressing this fatigue lifetime prediction for two different commercial adhesives in electronic tools, and studying the influence of ageing on the lifetime prediction. Two types of ageing were implemented: an open-air ageing and a confined inert ageing (under Argon).An experimental characterization of the viscoelastic behavior of the two adhesive joints was first carried out. In particular, the non-linearities due to each of the loading parameter (simple shear and hydrostatic pressure) were highlighted and modeled.The microstructural heterogeneity brought by the metallic conductive fillers was then numerically studied. The numerical model introduces several approximations that make the results qualitative, but they highlight the influence of the fillers on the global macroscopic behavior of the adhesive joint.The question of the fatigue strength of adhesive joints and its evolution with ageing is finally experimentally addressed. The influence of the atmosphere and confinement of ageing on the lifetime prediction is clearly noticed for the two joints studied in this work. Fatigue criteria with some of the parameters evolving this ageing are proposed to fit the results experimentally obtained.

Die vorliegende Arbeit beschäftigt sich mit der Anwendung der indirekten Methoden zur automatisierten Lösung von einer bestimmten Klasse von Optimalen Steuerungsproblemen im Rahmen einer modellprädiktiven Regelung für Windenergieanlagen. In einem zweiten Teil wird der Einfluss dieser Regelungsmethode auf die Festigkeit des Triebstranges untersucht. Diese führt zu einer überproportionalen Beanspruchung und damit zu einer Reduktion der Betriebsfestigkeit. Es gilt entsprechende Randbedingungen für die der Regelung zugrunde liegenden Optimalen Steuerungsprobleme zu finden, so dass weiterhin die Energieausbeute maximiert werden kann, gleichzeitig jedoch die Beanspruchung durch die Regelung begrenzt wird.

This thesis is mainly focused on the seismic behaviour of cross laminated timber (CLT) buildings. The document can be subdivided into three main sections closely related to each other. In the first part, after a short introduction on the state of the art on timber buildings regarding the constructive and legislative issues, the behaviour of CLT buildings is presented. The research is focused on the study on single shear-walls, on the multi-storey single-walls and on the behaviour of the whole buildings. The analyses are performed in order to assess the ductility level achievable by a CLT building as a result of different choices for the ductility of the connections at the foundation level. In order to estimate the ductility level, a large number of non-linear analyses were performed. This was possible thanks to a Matlab code, specifically developed, which allowed to reduce the computational burden. The results are used to evaluate a reliable set of behaviour factors to be applied in the seismic design of CLT buildings. In the second part of thesis, the low-cyclic fatigue strengths for different typologies of dissipative timber connections are presented. The low-cyclic fatigue strength represents a key-parameter in the assessment of the seismic behaviour of timber connections. In fact, high values of ductility associated with low values of strength degradation ensure a remarkable and reliable energy dissipation without a significant loss of strength. Despite the current version of chapter 8 of Eurocode 8 requires specific values of seismic demand for timber connections in terms of low-cyclic fatigue strength, no specific provision is reported to this regard in the European Standard for the cycling testing of timber connections and assemblage in seismic design (EN 12512). In This Standard the ductility capacity and the impairment of strength are calculated as separate mechanical parameters. For this reason, a proposal of revision of European Standard EN12512 is presented and discussed. The third and last part of the thesis describes an innovative connection for CLT buildings. This innovative connection was originally developed in order to absorb both traction and shear actions. Furthermore, a good performance has been obtained in terms of low-cyclic fatigue strength and ductility, with the aim of conceiving a connection able of satisfy the requirements of the current seismic European Standard. The design of this new connection was an iterative process, starting from some simplified numerical models. After some improvements, it was possible to obtain the expected performance levels. The strength and rigidity of the designed connection were initially obtained through numerical analysis, and then compared with the results of physical tests carried out in the Materials and Structures Testing Laboratory (MSTL), that is a part of the Department of Civil, Environmental and Mechanical Engineering (DICAM) of the University of Trento.

Das Örtliche Konzept dient der Berechnung von Lebensdauern zyklisch belasteter Konstruktionen. Dabei wird die Ermüdungsfestigkeit des ungekerbten Werkstoffes zugrundegelegt, um die Bauteillebensdauer abzuschätzen. Mit dieser Annahme verbunden ist ein starke Vereinfachung des Ermüdungsvorganges. Die Ursache ist die unzureichende Berücksichtigung wesentlicher Einflußgrößen, die die Festigkeit des interessierenden Bauteiles bestimmen und die andere Ausprägung als an der Werkstoffprobe erfahren. Dadurch ist die Zuverlässigkeit der Rechnung reduziert. Die vorliegende Arbeit untersucht und klassifiziert die Ursachen für dieses Übertragbarkeitsproblem. Mit einem sehr flexiblen multiplikativen Ansatz, der technologischen, statistischen und spannungsemchanischen Effekt berücksichtigt, läßt sich der Unterschied zwischen Festigkeit des Bauteils und der Werkstoffprobe rechnerisch erfassen. Zur numerischen Betrachtung technologischer und statistischer Einflüsse kann auf bereits bestehendes Wissen zurückgegriffen werden. Dies wird konzeptbezogen und mit Rücksicht auf die Anwendung angepaßt. Die Berücksichtigung des spannungsmechanischen Einflusses hingegen kann nicht von Bestehendem abgeleitet werden. Dazu wird aus einer umfangreichen Sammlung experimenteller Ergebnisse dieser Einflufaktor abgeleitet. Aus der so gegebenen Stichprobe lassen sich durch eine statistische Auswertung eine Reihe von Kennwerten identifizieren, die die Stützwirkung maßgeblich beeinflussen. Darauf aufbauend wird eine Bestimmungsgleichung für den spannungsmechanischen Einflußfaktor abgeleitet. Somit ist ein Stützwirkungskonzept geschaffen, das es erlaubt, die drei wesentliche Aspekte technologischen, statistischen und spannungsmechanischen Einfluß qualitativ uind quantitativ ins Örtliche Konzept zu integrieren. Mit dieser Vorgehsweise und einer vorliegenden Werkstoffwöhlerlinie läßt sich die bauteilspezifische Festigkeit abschätzen. Die so abgeleitete Wöhlerlinie erlaubt eine wesentlich genauere Lebensdauerberechnung, wie die Kotrolle an umfangreichen, unabhängigen Daten beweist. / The local strain concept serves to estimate the service life of cyclically loaded structures. Here the fatigue strength of the mere material coupon is taken as the basis in the calculation for notched components. This represents a distinct simplification of the complex fatigue process because of disregarding the relevant influences that determine strength and durability. By that the reliability of the calculation is not yet satisfying. The present investigation first classifies the reasons for this problem of transferabillity between notched component and unnotched specimen. A simple but flexible approach is used to describe the technological, statistical and and gradient effect. To consider the technological influences and statistical size effect numerically, known relationships and procedures are taken and adapted to the methodology of the concept. To catch gradient effects a new stress-relief-concept was developed. From a comprehensive database of experimental results gradient effects were were separated. By a statistical analysis relevant variables that govern the stress-relief are identified. Using these, an equation gets derived which enables to compute the gradient effects on fatigue strength. The developed stress-relief-concept allows to estimate a component-related strain(parameter-)-life-curve. Lifetime predictioins based on this are by far more reliable than those based on materials data only. This is verified by a check on an extensive and independent database.

The pores in pressed and sintered components constitute weak points in the material since the stress concentration is larger than the nominal stress there. Therefore, fatigue cracks initiate at the pores. Specifically, it can be assumed that the fatigue cracks initiate at the largest pore in the stressed volume. Studies have previously looked at finding ways to model the fatigue strength of the material based on the largest pore. This thesis looks at a model previously derived for hardened pressed and sintered materials that is based on linear elastic fracture mechanics and investigates if said model can be modified to include non-hardened pressed and sintered materials that do not necessarily behave linear elastically. A model describing the influence of the size of the largest pore on the fatigue limit using empirical coefficients is suggested. Furthermore, the area of the largest pore is modelled using extreme value statistics. The model proved successful in modelling the density effect of the porosity on the fatigue strength for two materials with different microstructures: one with a homogeneous microstructure and one with a heterogeneous microstructure. For the material with the homogenoeous microstructure the model also accounted well for the notch effect when tested on samples with a different geometry. However, for the heterogeneous material the model did not account for the notch effect. Deformation hardening due to local plastic deformation in the softer phases was suggested as a possible explanation and was supported by tensile tests.

The focus of this thesis is the construction of a single girder overhead crane. The goal is to render a crane construction according to preset parameters. The parameters include a lifting power of 8,000 kg, a 10,000 mm reach, a 2,400 mm wheelbase and a stroke of 8,000 mm. The thesis includes brief theoretical research focused on overhead cranes, their various types and description of their main components. Brief description of chosen parameters for the construction itself follows. The description of chosen parameters includes calculations of strain acting during operation, technical and stability parameters, essential for the construction. All calculations were made with regard to valid Czech technical standards and specialized literature which focuses on the construction of cranes and their parts. Finally, the thesis is extended by the required technical drawings.