|
|
Investigation of deformation mechanisms of advanced light-weight alloys
Németh, Gergely ; Mathis, Kristián (advisor) ; Drozd, Zdeněk (referee)
The objective of this thesis is to investigate the mechanical and damping properties in AZ91 alloys with different boron concentrations and in two experimental alloys based on commercial pure magnesium. Further aim is to identify the influence of heat treatment of alloys AZ91+B on the properties mentioned above. Micro-structural observations were achieved by optical and scanning electron microscope. Mechanical tests were performed in a wide range of temperatures from 23řC to 300řC and, simultaneously, the acoustic emission was recorded at room temperature. The temperature spectrum of internal friction was determined in the temperature range from 23řC to 400řC. Moreover, the amplitude dependence of damping properties of materials were studied. Phenomena leading to dissipation of mechanical energy in the temperature spectrum were determined by micro-structural observation.
|
|
|
Ceramic materials and composites for advanced applications
Mařák, Vojtěch ; Částková, Klára (referee) ; Michálková,, Monika (referee) ; Drdlík, Daniel (advisor)
Tato dizertační práce se zaměřuje na pokročilou oxidovou keramiku a částicové a vrstevnaté kompozity. Studované materiály zahrnují biokeramický hydroxyapatit, termomiotický wolframan hlinitý a bezolovnaté piezoelektrické materiály na bázi titaničitanu barnatého. Příprava těchto keramik má několik omezení ovlivňující finální vlastnosti, zahrnující použití toxických stabilizátorů, nízké zhutnění, náchylnost k praskání, vznik nežádoucích chemických reakcí, nízké mechanické a elektrické vlastnosti. Tato práce řeší tyto problémy přizpůsobením jednotlivých kroků zpracování a použitím progresivních výrobních metod pro optimalizaci požadovaných funkčních vlastností materiálů. Úprava hydroxyapatitového prášku studenou plazmou umožnila elektroforetickou depozici bez toxických stabilizátorů, což vedlo k hutnějším povlakům bez trhlin. Praktický benefit tohoto přístupu byl demonstrován v případě bezdefektních hydroxyapatitových povlaků ortopedických šroubů. Termomiotický wolframan hlinitý, vyznačující se svým téměř nulovým koeficientem tepelné roztažnosti, byl syntetizován optimalizovanou koprecipitací za účelem zlepšení slinovatelnosti prášku. Rychlé beztlaké slinování a slinování plazmovou jiskrou byly použity ke zhutnění materiálu, přičemž bylo dosaženo dosud nejvyšších publikovaných hodnot hustot při nejnižší slinovací teplotě. Vývoj mikrostruktury piezokeramiky titaničitanu barnatého byl studován pomocí rychlého beztlakého slinování a slinování s pomocí radiace. Získané poznatky byly využity pro slinování částicových kompozitů na bázi titaničitanu barnatého vyztuženého oxidovými keramikami. Vysoká reaktivita mezi zvolenými materiály měla negativní vliv na vlastnosti kompozitů a jeden z reakčních produktů byl podrobněji charakterizován. Byly připraveny vrstvené kompozity střídáním vrstev na bázi titaničitanu barnatého a dielektrického oxidu zirkoničitého. Vysoká reaktivita piezoelektrických materiálů byla potlačena volbou slinovací strategie. Souhrnným cílem této disertační práce je posunout vědění v oblasti vlastností a zpracování keramických materiálů, poskytnout náhled na optimalizaci funkčnosti a řešit kritická omezení v různých aplikacích.
|
|
|
Analysis of Dubičná landslide - slope stability and soil mechanical properties
Pospíchal, Vojtěch ; Jerman, Jan (advisor) ; Racek, Ondřej (referee)
Diploma thesis Bc. Vojtěch Pospíchal Analysis of slope movement Dubičná - mechanical properties of mudstones and stability ratios ABSTRACT This thesis deals with the stability conditions of the Dubičná landslide area, which is located at the contact of two regional geological units of the Czech Cretaceous Basin and the Bohemian Central Highlands. It compares the mechanical properties of the mudstones of the Březno Formation, which were obtained through laboratory tests, with the results from another landslide site, Prackovice, where very similar geological and morphological conditions occur. Determination of critical and residual strength is essential for determining slope stability. For this purpose, laboratory tests were carried out and at the same time correlation relations were tested, which can predict strength parameters based on index parameters. Furthermore, the geometry of the landslide area with seasonal variations of the groundwater level was created. The obtained parameters and geometries were used to calculate the stability in the Plaxis program. The factor of safety is around 1, depending on the height of the groundwater level.
|
|
|
Assessment of 3D printing technology as an alternative in manufacturing
Balvín, Patrik ; Šafl, Pavel (referee) ; Binar, Tomáš (advisor)
This bachelor thesis is devoted to 3D printing. The main methods od 3D printing, widely used materials (their production, their properties and the advantages and disadvantages of using them), degradation due to enviromental conditions, other common methods of producing polymer parts and mechanical test are described in the theoretical part. This paper also compares the advantages of using 3D printing for prototyping. The experimental section is dedicated to measuring the impact of material degradation on the toughness, hardness, and tensile strength of PLA and PA6 CF15 materials. The case study focuses on the design of an engine spark coil holder and a mobile workstation for 3D printing.
|
|
|
Small Punch test brittle materials
Saňka, Martin ; Válka, Libor (referee) ; Zapletal, Josef (advisor)
Bachelor’s thesis is focused on description of methods for material testing of miniature samples called „Small Punch Test“. Thesis describes the basic test procedures, interpretation of their results and sample removal techniques. Recognized methods of correlating test results with parameters obtained from conventional material tests and after test sample evaluation were described in the thesis. Furthermore, the thesis deals with the evaluation of mechanical properties of brittle materials using the „Small Punch Test“, where a statistical appoach to obtaining their characteristic strength and specifying the procedure for determining the fracture toughness was described.
|
|
|
Mechanical properties of large scale 3D printed parts
Strela, Dominik ; Malý, Martin (referee) ; Křivohlavý, Petr (advisor)
This study focuses on the effects of printing parameters on mechanical properties of parts manufactured with FDM (Fused Deposition Modelling) technology. Specimens made from PLA material using the KUKA KR8 R1620 robotic arm underwent tensile test, their shape was designed so to prevent effects of negative phenomena on the results. The results were evaluated and graphically shown. The results show that inter-rastral bonds intensely weaken the parts strength, however a slight material overfill helps strengthen the bonds. The highest tensile strength was measured on specimens with the largest inter-rastral distance and layer hight, with 1,1 as the coefficient of material flow. The results of this study should serve as reference values for future research of properties and behaviours of parts printed using nozzles of larger diameter. They describe the impact of rasterizing products on the final strength.
|
|
|
Preparation and optimization of a two-layer highperformance cement composite
Kouřilová, Lucie ; Šuleková, Nikola (referee) ; Novotný, Radoslav (advisor)
This bachelor thesis focuses on high-performance cementitious composites with emphasis on the issue of the two-layer concept. The main objective is to design a coarse-grained composite for the front layer with the aim of maximizing the packing density and optimizing the bonding of each layer. High mechanical properties in high performance concrete are achieved, due to the reduction of the water coefficient. In order to optimize the packing density of the coarse-grained cementitious composite, experiments were conducted with different ratios of aggregate types having different particle sizes. The bonding of the layers is influenced by the condition and state of surface, the compaction method and the mechanical properties of the materials. The strength of the bond was evaluated using the tensile strength under three-point bending. The bond strength was affected by the application of a cement paste and in the second case only water on the surface of the face layer.
|
|
|
Weldability of hardenable aluminum alloys
Filip, Josef ; Slováček, Marek (referee) ; Kubíček, Jaroslav (advisor)
The thesis deals with the influence of MIG pulsed metal transfer welding on the mechanical properties of the aluminium curable alloy and on the presence of defects in the welded joint. The aluminium alloy EN AW 6082 T6 was chosen for the experiment, i.e. in the state after the artificial ageing. The experimental part first describes the selected base and filler material, the used welding equipment, the choice of welding parameters and then the preparation process of the test samples is described. There were made 6 sets of samples, each of them was welded with a different combination of welding parameters and pulsed welding mode. Subsequently, the work deals with several material destructive tests that were part of the experiment. Tensile tests, hardness measurements and microstructure tests were performed. The results of the tensile tests showed that in all cases the tensile strength was decreased by more than 30% compared to the base material and similar values were achieved. Thus, the theoretical assumption that soluble precipitates occur during the welding of hardened Al alloys, causing a decrease in the mechanical properties in the HAZ, was confirmed. It is evident in the results of hardness measurements, which for all samples reached the lowest values in the HAZ at the same place where fractures occurred in the tensile tests. The macroscopic examinations then showed the presence of micropores in all samples except the set num. 4, which did not develop porosity. In several cases, the presence of unbroken or oxide inclusions was also detected. The results are evaluated at the end of the thesis.
|
|
|
Assessment of the use of 3D printing technology in the automotive industry
Ondriska, Josef ; Libich, Jiří (referee) ; Binar, Tomáš (advisor)
This thesis deals with 3D printing technology and analysis of various polymeric additive manufacturing materials, with a focus on their application in the automotive industry. In the experimental part, three types of material are tested for mechanical properties, both without degradation and after degradation by a climate chamber. In the tensile strength test, the possibility of using acoustic emission as a diagnostic method was verified. From the results obtained, a specific part used in the automotive industry was designed. The work also includes the design of a stationary
|
|
|
Characterization of surface and mechanical properties of microbial cells
Khýrová, Markéta ; Lukeš,, Jaroslav (referee) ; Plichta, Tomáš (advisor)
The subject of this diploma thesis is the characterization of bacterial strains capable of polyhydroxyalkanoates (PHA) production in terms of morphology and mechanical properties. With this aim, an atomic force microscope (AFM) was used together with a nanoindentation instrument to perform microcompression tests on selected microorganisms. The model bacterial strains, Cupriavidus necator and Rhodospirillum rubrum, were tested in their PHA-producing form and in their mutant non-producing variant, in order to study the effect of PHA amount on bacterial morphology and mechanical properties. In the experimental part of this work, the preparation of native bacterial samples for both techniques were first optimised. Glass substrates were treated with plasma and the cells were subsequently fixed with poly-L-lysine. In addition, sample preparation including fluorescent staining was optimized for the microcompression tests in order to easily detect cells and determine their size. Finally, the impact of different measurement parameters and mathematical models for calculating Young's modulus on the AFM data were evaluated. The results revealed the effect of PHA on bacterial cell morphology and showed that PHA producers exhibit higher Young´s modulus on average compared to their mutant. It was also shown experimentally that microcompression tests provide significantly higher Young's modulus values than those obtained by AFM.
|
guest ::
