Title: Study of novel magnesium alloys with controlled microstructure and texture Author: Daria Drozdenko Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Ing. Patrik Dobroň, Ph.D., Department of Physics of Materials. Abstract: The work elucidates the role of dislocation slip and twinning during plastic deformation in selected magnesium (Mg) alloys with controlled microstructure and texture. The acoustic emission (AE) technique was concurrently applied during deformation to determine the activity of particular deformation mechanisms. A detailed insight into microstructure was provided by electron microscopy. In order to obtain a comprehensive set of AE data for particular deformation mechanisms, Mg single crystals with various crystallographic orientations were channel-die and uniaxially compressed. The obtained results were applied on deformation mechanisms in polycrystalline textured Mg alloys. Particularly, the twinning - detwinning processes, in the sense of twin boundary mobility, during one cycle loading (pre-compression followed by tension) were described. Clear correlations between changes in the AE response and the inflection points on the deformation curve were found. An analysis of twin...

Polymer gels undergo a volume phase transition in solvent in response to an infinitesimal environmental change. This remarkable phenomenon has resulted in many potential applications of polymer gels. The understanding of its mechanical properties has both scientific and technological importance. For this purpose, we have developed a novel method for measuring Poisson's ratio, which is one of the most important parameters determining the mechanical property of gels. Using this method, Poisson's ratio in N-isopropyacrylamide (NIPA) and polyacrylamide (PAAM) gels has been studied.

The need for sustainable packaging is growing, and plastic waste needs to be reduced. A suitable alternative could be fibre-based packaging and cartonboard, and several actions could enhance this alternative. This study investigates crosslinking, a method to create stronger bonds between the OH-groups in the material. The aim is to gather information on the potential of the concept since there is previously a limited amount of research on the specific area. The goal, in the long run, is to create stronger packaging. The study will contribute with knowledge around how crosslinking can be used to enhance the strength of cartonboard and contribute to the development of more durable material. Two research questions were formulated to investigate this.  RQ1: How does the crosslinking concept affect properties of cartonboard when applied? RQ2: What effect could the crosslinking concept have on the product area cartonboard? The research has a deductive starting point, and the project planning was agile, which allowed the study to form as the results gave new intel about the concept. The focus is on collecting qualitative data with high validity, which has been done by testing the material according to different standards. The material investigated is a folding boxboard (FBB) in four separate grammages to give an overview of the effect of the concepts. Properties evaluated include short span compression test (SCT), tensile strength, recyclability, cobb and box compression resistance tests (BCR), and more.  The results show a slight increase in SCT for the highest, 460 gsm, and lowest, 245 gsm, grammages of the materials used in this study. The recyclable is affected minimally with only a few per cent, but it remains high. However, the material becomes a bit stiffer and suffers losses in tensile strength, elongation, and tensile energy absorption. The enhanced strength seen in SCT does not show for BCR. The crosslinked material tends to crack in the creases before and after bending, especially in the highest grammage. The Cobb results indicate crosslinking shows potential to be used as a barrier to make the material more water repellent.  Conclusions drawn from the results are that even though the SCT value is enhanced for two grammages, it suffers losses in tensile strength, and the strength enhancement does not show for BCR. Therefore, the impact on the product area is not clear, and further research is recommended to understand the area more.  Suggestion for further research is to do more research in the area in general and then scale up the study to a pilot study. This would gain intel on how the concept will work in a non-laboratory situation and investigate how it could be implemented in production

Silica nanoparticles (SiO2 NPs) were prepared and functionalized with polyethylene (PE@SiO2 NPs) using the surface-initiated polyhomologation (SI polyhomologation) technique. Polyolefin nanocomposites were fabricated later by melt mixing of different ratios of the as-prepared SiO2 NPs and PE@SiO2 NPs with linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) matrices. Firstly, SiO2 NPs were modified with different alkoxysilane ligands, dichloro(divinyl)silane (DCDVS), allyl trimethoxysilane (ATMS), and vinyl triethoxylsilane (VTES). Subsequently, thexylborane, an initiator for SI polyhomologation, was immobilized to the modified surface of SiO2 NPs through hydroboration reactions. Polyhomologation was then allowed to proceed by adding monomer solution to form polyethylene brushes covalently bonded to the surface of the NPs. Physicochemical characterization had confirmed the morphology, chemical structure, and thermal stability for each step of modification reactions. LLDPE and LDPE nanocomposites were prepared by extrusion with SiO2 NPs and PE@SiO2 NPs as nanofillers. Finally, tensile tests and morphological SEM-based analyses are presented to discuss the influence of the grafted PE on both the dispersion of the fillers and the mechanical properties of the filler/matrix interphase.

The desire to replace missing teeth with the aim to improve health and quality of life dates back to a thousand years ago. Although research on dental crown designs, materials and techniques has increased in recent years and is expected to grow in the future. In the past few decades, dental crown studies have gained high importance in dentistry due to their functionality, biocompatibility and good mechanical properties. This paper provides a comprehensive review of history and evolution of dental crowns. The goal of this study is to understand the dental crown materials and the differences in their properties with goals to facilitate the optimal selection and to support further development. It also describes the different methods by which wear is tested on these crowns. Finally, it describes the current technologies used for the analysis, and a comparative study is performed on various dental crown materials and it is demonstrated that the wear resistance is different for different materials.

Among vertebrates, whole-body movement is centered around the vertebral column. The bony vertebral column primarily consists of trabecular (spongy) bone that adapts in vivo to support mechanical demands respective to region, ontogeny, ecology, and locomotion. Previous work has extensively investigated the formfunction relationships of vertebral trabecular bone in terrestrial mammals, who use limb contact with a substrate as the primary support against gravity. However, we lack data from obligate swimming mammals whose locomotor ecology diverged from their terrestrial counterparts in two major ways: (1) body mass is supported by water’s uplifting buoyant forces and (2) swimmers power movement through dorsoventral loading of the axial body. This study examined vertebral trabecular bone mechanical properties and micoarchitecture from fully aquatic mammals, specifically sirenians (i.e. manatees) and cetaceans (i.e. dolphins and whales). We compression tested bone from several regions of the vertebral column among developmental stages in Florida manatees (Trichechus manatus latirostris) and among 10 cetacean species (Families Delphinidae and Kogiidae) with various swimming modes and diving behaviors. In addition, we microCT scanned a subset of cetacean vertebrae before subjecting them to mechanical tests. We demonstrated that in precocial manatee calves, vertebrae were the strongest and toughest in the posterior vertebral column, which may support rostrocaudal force propagation and increasing bending amplitudes towards the tail tip during undulatory swimming. Among cetaceans, we showed that greatest strength, stiffness, toughness, bone volume fraction, and degree of anisotropy were in rigidtorso shallow-divers, while properties had the smallest values in flexible-torso deep-divers. We propose that animals swimming in shallower waters actively swim more than species that conduct habitual glides during deep descents in the water column, and place comparatively greater loads on their vertebral columns. We found that cetacean bone volume fraction was the best predictor for mechanical properties. Due to the shared non-weight bearing conditions of water and microgravity, we present these data as a contribution to the body of work investigating bone adaptations in mammals that live in weightless conditions throughout life and evolutionary history. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

Bioactive glasses exhibit unique characteristics as a material for bone tissue engineering. Unfortunately, their extensive application for the repair of load-bearing bone defects is still limited by low mechanical strength and fracture toughness. The main aim of this work was two-fold: the reinforcement of brittle Bioglass®-based porous scaffolds and the production of bulk Bioglass® samples exhibiting enhanced mechanical properties. For the first task, scaffolds were coated by composite coating constituted by polyvinyl alcohol (PVA) and microfibrillated cellulose (MFC). The addition of PVA/MFC coating led to a 10 fold increase of compressive strength and a 20 fold increase of tensile strength in comparison with non-coated scaffolds. SEM observations of broken struts surfaces proved the reinforcing and toughening mechanism of the composite coating which was ascribed to crack bridging and fracture of cellulose fibrils. The mechanical properties of the coating material were investigated by tensile testing of PVA/MFC stand–alone specimens. The stirring time of the PVA/MFC solution came out as a crucial parameter in order to achieve a more homogeneous dispersion of the fibres and consequently enhanced strength and stiffness. Numerical simulation of a PVA coated Bioglass® strut revealed the infiltration depth of the coating until the crack tip as the most effective criterion for the struts strengthening. Contact angle and linear viscosity measurements of PVA/MFC solutions showed that MFC causes a reduction in contact angle and a drastic increase in viscosity, indicating that a balance between these opposing effects must be achieved. Concerning the production of bulk samples, conventional furnace and spark plasma sintering technique was used. Spark plasma sintering performed without the assistance of mechanical pressure and at heating rates ranging from 100 to 300°C /min led to a material having density close to theoretical one and fracture toughness nearly 4 times higher in comparison with conventional sintering. Fractographic analysis revealed the crack deflection as the main toughening mechanisms acting in the bulk Bioglass®. Time–dependent crack healing process was also observed. The further investigation on the non-equilibrium phases crystallized is required. All obtained results are discussed in detail and general recommendations for scaffolds with enhanced mechanical resistance are served.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20198号 / 理博第4283号 / 新制||理||1615(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)准教授 中西 和樹, 教授 北川 宏, 教授 島川 祐一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

No description available.

No description available.