The diploma thesis deals with preparation of acrylic copolymers via emulsion polymerization technique. Two sets of copolymer samples were prepared within this thesis, n BA/MMA and 2-EHA/MMA copolymers. n-BA/MMA copolymer sample was used for investigation of effect of surfactant concentration as well as effect of addition of acrylic acid to the feed composition. During all the copolymerizations, conversion was observed via solids content evaluation as the reaction progressed. Copolymerization was lead under inert atmosphere at continuous stirring and 80 °C for 4 hours. Glass transition temperature of samples was determined with DSC and Vicat softening point was measured as well. Data acquired from measurements were compared with values calculated with Fox equation which was used for modelling molar ratio of monomers in initial feed.

This thesis describes selection and shows calibration of material model, capable of describing cyclic softening of material. Stress-strain FEM analysis of circumferential blade attachment for last section of rotor blades of steam turbine is performed, expected lifetime of existing attachment is evaluated. Multi-parameter optimization of new-shape attachment was done, resulting in dimensions for new-shape attachment with longer lifetime. Improvements in strain amount in comparison with existing attachment were evaluated and possible RPM increase of turbine with new attachment type was calculated.

Le travail s’intéresse aux effets de l’histoire de chargement sur le comportement et la durée de vie en fatigue de deux nuances (THYSSEN et CLI)d’un acier inoxydable austénitique 304L à la température ambiante. Les essais ont été réalisés en utilisant deux catégories d’éprouvettes. Les éprouvettes de la première catégorie (vierges) ont été soumises à des essais classiques de fatigue,alors que celles de la deuxième ont subi, avant les essais de fatigue, un pré-écrouissage monotone ou cyclique en déformation imposée. Les éprouvettes vierges manifestent un adoucissement cyclique suivi d’un durcissement cyclique alors que les éprouvettes pré-écrouies ne présentent qu’un durcissement cyclique. Les résultats montrent une grande influence du pré-écrouissage qui semble bénéfique en contrainte imposée, mais néfaste en déformation imposée,même en présence d'une contrainte moyenne de compression. Ces résultats sont discutés en termes d'évolution cyclique du module d'élasticité, des écrouissages isotropes et cinématiques, et de la densité d’énergie absorbées par cycle, dans différentes configurations : avec ou sans pré-écrouissage, en contrainte ou déformation imposées... / This study deals with the effect of the loading history on the cyclic behavior and the fatigue life of two kinds (THYSSEN and CLI) of 304L stainless steel at room temperature. The experiments have been performed using two specimens’ categories. The first one (virgin) has been submitted to only classical fatigue tests while in the second category, prior to the fatigue test, the specimen is subjected to a pre-hardening process under either monotonic or cyclic strain control. Cyclic softening followed by cyclic hardening are observed for the virgin specimens while only cyclic softening is exhibited by the pre-hardened specimens. The obtained results show that fatigue life is strongly influenced by the pre-hardening: it seems beneficial under stress control but detrimental under strain control, even in the presence of a compressive mean stress. The results are discussed regarding the cyclic evolution of the elastic modulus aswell as the isotropic and kinematic parts of the strain hardening, and strain energy density per cycle, in different configurations: with or without prehardening,stress or strain control...

The influence of disorder is an important area in materials research. A supersaturated solid solution is in a metastable state, in which the host lattice is forced to solve guest atoms over the thermodynamical stability limit. The guest atoms are point defects, which amount can be varied by changing the concentration. The increasing amount of point defects makes the lattice unstable against schare, which may ends up in an order-disorder transition. In this work especially the lattice dynamics was studied at the atomic level by means of inelastic neutron scattering. In case of both studied systems (ZrAl, CuFe) a softening of especially the tranverse phonons could be shown, which supports the existing theory. / Der Einfluß von Unordnung ist ein wichtiges Forschungsgebiet der Materialwissenschaft. Bei übersättigten festen Lösungen handelt es sich um einen metastabilen Zustand, bei dem das Wirtsgitter gezwungen ist, mehr Fremdatome aufzunehmen, als thermodynamisch stabil ist. Die Fremdatome im Wirtsgitter sind Punktdefekte, deren Menge mit der Konzentration variiert werden kann. Die Zunahme substitutionaler Defekte bewirkt eine Gitterinstabilität gegenüber Scherkräften und anschliessend möglicherweise einen Ordnungs - Unordnungs - Übergang. In dieser Arbeit wurden vor allem dynamische Aspekte betrachtet: die Gitterdynamik wurde auf atomarer Ebene mittels inelastischer Neutronenstreuung untersucht. Bei beiden untersuchten Systemen (ZrAl, CuFe) konnte ein Weichwerden (softening) von Phononen beobachtet werden, insbesondere von transversalen Moden, die einen direkten Nachweis der oben erwähnten Gitterinstabilität ergeben.

Evaluating the safety of unreinforced concrete structures, such as concrete dams, requires an accurate prediction of cracking. Developing a suitable constitutive material model and a reliable computational procedure for analysing cracking processes in concrete has been a challenging and demanding task. Although many analytical methods based on fracture mechanics have been proposed for concrete dams in the last few decades, they have not yet become part of standard design procedures. Few of the current research findings are being implemented by practising engineers when evaluating dam safety. This research is focused on the development of a suitable crack modelling and analysis method for the prediction and study of fracturing in concrete gravity dams, and consequently, for the evaluation of dam safety against cracking. The research aims to contribute to the continuing research efforts into mastering the mechanics of cracking in concrete dams. An analytical method for the purpose of establishing a crack constitutive model and implementing the model for the fracture analysis of concrete structures, in particular massive concrete gravity dams under static loading conditions, has been developed, verified and applied in the safety evaluation of a concrete gravity dam. The constitutive material model is based on non-linear fracture mechanics and assumes a bilinear softening response. The crack model has various improved features: (1) an enhanced mode I bilinear strain-softening approach has been put forward; (2) a new formula for bilinear softening parameters has been developed and their relation with linear softening has been outlined; (3) the influence of bilinear softening parameters on the cracking response has been studied; and (4) an enhanced modification to the shear retention factor which depends on the crack normal strain is included. The material model has been incorporated into a finite element analysis using a smeared crack approach. A sub-program was specially coded for this research. The validity of the proposed cracking model and the computational procedure developed for the purpose of analyzing the tensile fracture behaviour of concrete structures has been confirmed by verification on various concrete structures, including beams, a dam model and actual gravity dams. The crack modelling technique developed was successfully used in evaluating the safety of an existing concrete gravity dam in South Africa and adequately predicted the cracking response of the dam structure under static loadings. The main conclusions drawn are as follows: <ul><li>Both mode I and mode II fracture have been modelled successfully.</li> <li>The proposed bilinear softening model remains relatively simple to implement but significantly improves on predicting the softening response of “small-scale” concrete structures.</li> <li>Both plane stress and plane strain crack analyses have been considered and can be confidently adopted in two-dimensional applications.</li> <li>The proposed method is mesh objective.</li> <li>The crack modelling method developed can correctly predict the crack propagation trajectory and the structural behaviour with regard to fracturing in concrete structures.</li> <li>If not considering shear stress concentration near the tip of a crack, constitutive crack analysis normally indicates a higher safety factor and a higher Imminent Failure Flood (IFF) than the classical methods in the analysis of concrete gravity dams for safety evaluation.</li></ul> / Thesis (PhD(Civil Engineering))--University of Pretoria, 2007. / Civil Engineering / PhD / unrestricted

The increased use of thermoplastics in load carrying components, especially in the automotive industry, drives the needs for a better understanding of its complex mechanical properties. In this thesis work for a master degree in solid mechanics, the mechanical properties of a PA 6/66 resin with and without reinforcement of glass fibers experimentally been investigated. Topics of interest have been the dependency of fiber orientation, residual strains at unloading and compression relative tension properties. The experimental investigation was followed by simulations implementing existing and available constitutive models in the commercial finite element code LS-DYNA. The experimental findings showed that the orientation of the fibers significantly affects the mechanical properties. The ultimate tensile strength differed approximately 50% between along and cross flow direction and the cross-flow properties are closer to the ones of the unfilled resin, i.e. the matrix material. An elastic-plastic model with Hill’s yield criterion was used to capture the anisotropy in a simulation of the tensile test. Residual strains were measured during strain recovery from different load levels and the experimental findings were implemented in an elastic-plastic damage model to predict the permanent strains after unloading. Compression tests showed that a stiffer response is obtained for strains above 3% in comparison to tension. The increased stiffness in compression is although too small to significantly influence a simulation of a 3 point bend test using a material model dependent of the hydrostatic stress.

Indiana University-Purdue University Indianapolis (IUPUI) / Objective: This study aimed to evaluate surface microhardness changes in early, incipient, non-cavitated white-spot, enamel caries lesions treated with silver diamine fluoride (SDF) longitudinally. The utilization of silver nitrate and potassium fluoride test groups served as additional controls to assist in evaluating if the remineralization effects were due to the silver or fluoride component in SDF. Hypotheses: 1. SDF treatment will result in increased surface microhardness of early, incipient, non-cavitated white-spot, enamel caries lesions compared to all other tested interventions. 2. Specimen storage for 2-weeks in artificial saliva will result in greater surface rehardening in lesions treated with SDF compared to other tested interventions. Design: This laboratory study had 5 intervention groups (SDF, silver nitrate (AgNO3), potassium fluoride (KF), 5.0-percent sodium fluoride varnish (FV), deionized water (DI)) × 2-time intervals after intervention (immediate & delayed pH-cycling), resulting in 10 groups (n = 18). Early, incipient, non-cavitated white-spot, enamel caries lesions were created in bovine enamel and extent of demineralization was determined using Vickers surface microhardness (VHNlesion). Intervention treatments were applied. Half the specimens from each group underwent immediate 5-day pH-cycling and half were stored in an incubator with artificial saliva for two weeks before undergoing 5-day pH-cycling. After pH-cycling, lesion hardness was evaluated using VHNpost. Specimens were then exposed to a second demineralization challenge and lesion softening was evaluated using VHNsecdem. Surface rehardening was calculated: ΔVHN =VHNpost - VHNlesion. Surface softening was calculated: ΔVHNsecdem =VHNsecdem – VHNpost. Data was analyzed using two-way ANOVA. Results: Immediately cycled, SDF had significantly (p < .0001) greater remineralization than DI, AgNO3, and FV. All delayed cycling groups had significantly (p < .0001) greater remineralization than FV. Significantly greater remineralization was noted in delayed AgNO3 (p < .0001), DI (p = .0003), and FV (p = .0006) compared to immediately cycled. After the second demineralization challenge, FV had significantly less surface softening than AgNO3 (p = 0.0002), DI (p = 0.0003), KF (p = 0.0225), and SDF (p = 0.0388) intervention groups. No significant difference was found between the pH-cycle timings. Conclusion: Based on our findings, FV maybe better suitable than SDF to treat early, incipient, non-cavitated white-spot, enamel caries lesions. Longitudinally, SDF exhibited greater remineralization than both FV and DI groups, though not statistically significant. However, upon a second demineralization challenge, FV significantly outperformed SDF in preventing surface softening. / 2021-09-30

The subject of this diploma thesis is a research of bituminous binder modification by fast react-ing polymer SBS. The theoretical part covers an introduction to bituminous binders, their pro-duction, chemical and physical-mechanical properties. The identification of bituminous binders and their use in bituminous mixtures is briefly described. To conclude, current modification methods are described in detail and important modifiers are introduced. In the practical part, three applied tests (softening point, elastic recovery and penetration) are described in detail. The bituminous binders tested (20/30, 30/45, 70/100, PMB 25/55-55 and PMB 45/80-50) and the fast-reacting polymer SBS are introduced. Samples with two weight percentages of SBS, 7,5% and 10%, are produced. Two mixing times, 60 seconds and 600 seconds were used to mix the bituminous binder and SBS. In conclusion, the results are evaluated and commented. Further research suggestions regarding this field are recommended.

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Quick clay slides are quite rare but often leads to major consequences for the society. These type of slides are complex and the true causes leading to a slide is difficult to map since the evidence is destroyed during the slide. Because of this, different theories develop of the causes of the slide based on the same information. It is also problematic to back-calculate the sliding event because the commonly applied concept of perfectly plastic limite quilibrium cannot be applied on many of the landslides in quick clay. The objectives of this thesis were to construct a fault tree that facilitate risk identification and risk analysis of quick clay slides and to evaluate the applicability of the constructed fault tree, especially in the feasibility study and design phase. Uncertainties within the subject require a careful approach when dealing with quick clay. An implementation of a fault tree for quick clay slides in a risk management could reduce the risk of a slide and better understand the phenomenon. Two case studies were approached with the created fault tree and two advanced calculation methods that account for the special behaviour of quickclay. The use of a qualitative fault tree analysis in combination with calculation methods enables an evaluation of isolated singular events that in the end can lead to a quick clay slide. With the possibility to study isolated events, the implementation of more advanced calculation methods may be facilitated in an early stage to predict and prevent quick clay slides. / Kvicklerskred är sällsynta men leder ofta till stor skada för samhället. Dessa skred är komplexa och orsaken till utlösandet av skredet är svårt att identifiera då bevisen förstörs under händelseförloppet. Detta leder till att olika teorier om orsaken av kvicklerskred kan variera från samma information. Det är också svårt att beräkna skredets omlopp i efterhand den vanliga beräkningsmetoden baseras på idealplastiska samband, något som inte går att applicera på kvicklera. Målet med denna studie var att konstruera ett felträd som underlättar riskidentifiering och riskanalyser av kvicklerskred. Målet var även att utvärdera användandet av felträdet i en byggnadsprocess, framförallt under förstudien och under projekteringsskedet. Osäkerheter inom området kräver en försiktig arbetsmetod när kvicklera finns i områden. Att använda sig av ett felträd för kvicklerskred i en riskhantering skulle kunna minska risken för ett skred och samtidigt öka systemförståelsen över fenomenet. Två fallstudier gjordes med det konstruerade felträdet, under dessa fältstudier gjordes även beräkningar med två avancerade beräkningsmetoder som tar hänsyn till det töjningsmjukande beteendet hos kvicklera. Användningav ett kvalitativt felträd i kombination med beräkningsmetoder möjligör en utvärdering av isolerade händelser som i slutändan kan leda till ett kvicklerskred. Möjligheten av att studera isolerade händelser kan underlätta en implementering av mer avancerade beräkningsmetoder i ett tidigt skede och på så vis förutse och förhindra kvicklerskred.