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Analysis of the causes of cracks on the wheeel rims
Plundrák, David ; Němec, Karel (referee) ; Foret, Rudolf (advisor)
This thesis looks for the causes of cracks in bicycle rims in the most stressed areas (in places holes for wires). For this reason, in this work is the stress and strain analysis of a simple model of the rim to the working load is given and further the complete production process of the rim is described. As an experimental material were used rims from different producers of aluminum alloy EN AW 6061 and EN AW 6082 T6 temper, in which a crack started to spread. For assessment of rims materials the methods of optical spectroscopy, optical microscopy, scanning electron microscopy, Vickers hardness test were used and for finding another crack penetration test was performed. Based on the performed experiments bad design solution of rivets was found in the rim 1. Broken rivets initiated fatigue cracks. Material of rim 1 was alright. The other two rims were deficiencies in materials. For the rim 2 was a problem with coarse-grained recrystallized structure. The insufficiently rapid cooling for the rim 3 caused exclusion hardening phase (particularly copper phase) at grain boundaries. Moreover, the rim 3 is not cured to the required parameters. Aluminium alloys are an ideal material for bicycle rims. However, they require reliable design solutions and meeting the physical metallurgy, which lies in the knowledge and use of influences of chemical composition, forming and heat treatment on mechanical, chemical, physical and technological properties.
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Welding of USIBOR 1500 steel by YbYAG fiber laser.
Bogar, Radek ; Kubíček, Jaroslav (referee) ; Mrňa, Libor (advisor)
The use of high-strength steel is more and more frequent in the car industry. I focused on USIBOR® 1500 steel welded by Nd-YAG laser. For my experiment, there were used various welding parameters and shielding gases. To compare the weld samples, I used the tensile, bending, macrostructure, microstructure and Vickers hardness test with different combinations of thickness as well as welded material.
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Study of sintering of advanced ceramic materials
Stromský, Tomáš ; Hadraba, Hynek (referee) ; Maca, Karel (advisor)
The influence of various pressure-less heating schedules (CRH - Constant Rate of Heating, TSS - Two Step Sintering, RCS – Rate Controlled Sintering) on the final microstructure of cubic zirconia ceramics was studied in this master´s thesis. There were used nanopowders ZrO2 (stabilized with 8 mol.% Y2O3) with initial particle size 80 nm (TZ-8Y) and 140 nm (TZ-8YSB). Powders were cold isostatically pressed and pressure-less sintered in air by different heating regimes. It was found that for both studied materials the modification of conventional sintering (CRH) using lower sintering temperatures and longer sintering dwell times can result in samples with finer microstructure. For example, the sintering of TZ-8YSB ceramics at a relatively low temperature (1270 °C) but for very long time (60 h) led to ceramics with the same final density (99,25 % of theoretical density) and almost identical grains (1,31 m vs. 1,27 m) in compare with TSS (1440 °C/ 1290 °C/ 15 h). On the other hand, RCS method showed no positive effect on the microstructure of both materials in comparison with CRH method. The obtained results indicate that the microstructure of c-ZrO2 ceramics can be influenced rather in its third sintering stage (by CRH and TSS methods) than in the second sintering stage (by RCS method).
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Fracture behaviour of heat affected zone near heterogeneous weld joint
Jelínek, Vladimír ; Válka, Libor (referee) ; Juliš, Martin (advisor)
The study deals with mechanical characteristic of heterogeneous weld joint. The low carbon steel 22K and austenitic steel have been used as a experimetnal materials. The low carbon steel has special properties in basic condition. The sample has been evaluated in basic condition and after annealation. There have been evaluated impact of annealation proces to structure and mechanical charakteristics in experimental part of study. The particularised analysis of microstructure has been done by pictorial analysis. Mechanical characteristics has been examinated in both conditions by 2 different methods – measurment of microhardness according to Vickers and test of fracture toughness on compact tension specimens.
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Optimisation of heat treatment of aluminium alloy AlSi7Mg0,6
Julišová, Martina ; Klakurková, Lenka (referee) ; Juliš, Martin (advisor)
The presented diploma thesis deals with various types of quenching and their respective effects on mechanical and structural properties of AlSi7Mg0.6 alloy castings. Cast with precision casting technology into a self-supporting ceramic shell made by plaster investment technology, flat test bars cast by Alucast were used as experimental samples. Sample castings were used in both cast state and after T6 heat treatment. Air-flow and air-water combination with varying water passage (spraying) were used as the quenching media in the quenching process of the castings. In order to evaluate the effect of five different quenching processes on the structure and mechanical properties of the castings, the method of light microscopy, Brinell hardness test and static traction test were used. Evaluation and porosity and SDAS quantifications were carried out by means of image analysis. Experiments did not prove right the hypothesis holding that low SDAS values inevitably mean higher mechanical properties of the castings. On the other hand, distinct is the negative influence of heterogeneous structure and porosity. Despite the fact that the heat treatment was successful in reducing the influence of structural inhomogeneities, it cannot be concluded that spray quenching has an utterly positive bearing on the mechanical and structural properties of the castings.
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Cemented carbides and theirs effective use
Dembek, Jiří ; Sedlák, Josef (referee) ; Humár, Anton (advisor)
This diploma thesis is aimed on cutting tools made of cemented carbides. It characterizes marking, production and properties of non-coating and coating cemented carbides and describes the latest trends in coating. Target of this diploma thesis is comparison of assortment of two important world’s producers and one Czech producer in term of used productive technologies, products microstructure, coatings types, coatings methods and possibilities of their usage. Cutting data were evaluated and compared from obtained technical knowledge, which were recommended by chosen producers for effective turning application of their cutting tools. Recommended cutting speeds were found out for specific type of cutting material according to ISO, width depth of cut and for specific values of feeds per revolution.
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Two-step sintering of advanced ceramic materials with various crystal structures
Žalud, Pavel ; Trunec, Martin (referee) ; Maca, Karel (advisor)
The influence of Two-Step Sintering (TSS) process on the final microstructure of oxide ceramics materials with two different crystal structures was studied. Tetragonal zirconia (stabilized with 3mol%Y2O3, particle size 90nm and 140nm ) and cubic zirconia (8mol%Y2O3, 70nm) powders were cold isostatically pressed and pressure less sintered with different heating schedules. The microstructures achieved with TSS method were compared with microstructures achieved with conventional Single-Step Sintering schedule (SSS). The results showed that the efficiency of the TSS of these oxide ceramics was more dependent on their crystal structure than on their particle size and green body microstructure. The method of TSS brought only negligible improvement of the microstructure of tetragonal zirconia ceramics. On the other hand, TSS was successful in the sintering of cubic zirconia ceramics; it led to a decrease in grain size by a factor of 2.
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Fibre coposites with alkali -activated slag matrix
Pluskalová, Barbora ; Bayer, Patrik (referee) ; Rovnaník, Pavel (advisor)
This master thesis is concerns the preparation of Alkali Activated Materials, specifically Alkali Activated Slag (AAS), with the addition of fiber reinforcement. Alkali Activated Materials have great potential for use in construction practice. However, their use is limited by certain undesirable properties, which can be diminished by adding fiber reinforcement. This thesis deals with the influence of carbon fibers (2 % by weight of the binder) and carbon nanotubes (0,2 % by weigh of the binder) on the mechanical properties, microstructure and shrinkage of AAS. The results of the experiments which were carried out correspond with the literary research. Conclusions of this thesis agree with research published in original scientific papers.
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Study of the properties of mortars with pozzolanic active materials
Vaníček, Štěpán ; Rovnaníková, Pavla (referee) ; Žižková, Nikol (advisor)
This thesis is focused on the study of the properties of mortars and pastes with active pozzolanic materials. It deals with monitoring cementitious composites which describes both the effect of compensation pozzolanic cement mortar admixtures active based on amorphous silica and the modifying polymeric additive. The main criteria for the assessment of these modified mortars and pastes are particularly adhesive and achieved strength compared with the reference mortar. The detailed work also examined the microstructure past through images from REM, records RTG, DTA and high pressure mercury porosimetry.
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