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Mechanical-structural characteristics of multi-materials prepared by additive technologies
Hyspecký, Michal ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
The diploma thesis deals with the mechanical-structural characteristics of the multimaterial interface prepared by the additive cold-spray (CS) technology. In the experimental part of the work, the titanium alloy Grade 23 was applied to the surface of aluminum alloy EN AW 2618, after heat treatment T6. Furthermore, a separate bulky block made of Grade 23 alloys for the production of tensile bodies was created using the CS method. The sprays were evaluated in two planes perpendicular to each other, respectively in longitudinal and transverse section. The average porosity of the coatings was evaluated at 2,6 ± 0,6%. The hardness value at low load did not change significantly with increasing distance from the interface and the mean value was 347 ± 51 HV 0,3. The tensile test did not show a significant effect of the sample orientation on the resulting value of the yield strength, which had the diameter of 345 ± 12 MPa. Successful deposition takes place at the temperature of 1010 ° C and the pressure of 5 MPa. The achieved results of the mechanical properties of the coating determined on the basis of tensile tests are at a relatively good level. Therefore, it is possible to consider the use of coating by this method, under given conditions, for rotating components operating at elevated temperatures, and increase their efficiency or service life.
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Adhezion wear mechanisms of moving engine parts
Cahová, Kristýna ; Válka, Libor (referee) ; Jan, Vít (advisor)
The thesis describes adhesion wear on a contact area between Common rail and the component and deals with various effects on this kind of wear. The aim of the thesis is to gain information about adhesion wear phenomena and to understands its physical principals. Theoretical part deals with description of Common rail and then it is focused on research of adhesion wear. Experimental part firstly summarizes available data from tests that have been already done and then continues with analysis of microstructure of materials which are in contact during assembling process and the formation of adhesion wear is increased there.
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The influence of conditioning on the mechanical properties of polymers produced by injection molding technology
Neužil, Tomáš ; Řehořek, Lukáš (referee) ; Válka, Libor (advisor)
The aim of the thesis is to determine change of mechanical properties of three types of damp polymeric materials (polyamides) depending on the water content inside material. Before testing, specimens of all three types of materials were placed inside the air conditioning chambers until equilibrium (conditioned) state was reached when the specimens received the maximum possible amount of water from the environment. A total of three conditioning levels were set, representing besides the standard level of conditioning both extreme states like state when the material was fully dried and the state where the material content the largest possible amount of water. With the increasing content of water bound in material, there is a characteristic change in the mechanical properties of the material, such as a decrease in strength and modulus of elasticity and an increase in toughness and ductility. To examine material properties change, tensile and Charpy impact tests were performed, Charpy impact tests were performed for both specimens with and without a notch. Besides changes in mechanical properties, the rate of water absorption was also observed depending on the materials and its filling.
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Correlation of standard mechanical test results and small punch test results
Holzer, Jakub ; Němec, Karel (referee) ; Válka, Libor (advisor)
The Bachelor’s thesis is aimed to sum up relations of mechanical properties of metallic materials obtained by standard mechanical tests with material properties obtained by small punch test. Methods and procedures used to evaluate material properties are evaluated and influence of external circumstances is analysed. Most important difficulties, that limit correlation of standard mechanical tests results and small punch test results, are also stated. Thesis contains an experimental validation of few selected correlation formulas.
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Repairs of component contact area using Cold Spray technology
Matiash, Dmytro ; Válka, Libor (referee) ; Řehořek, Lukáš (advisor)
The aim of this master’s thesis was to evaluate cold spray technologies as an alternative method of repairing contact surfaces of parts, especially made of high-alloy manganese steels, to choose a suitable system of materials and to analyze the properties and structure of the produced coating. The thesis presents the basic of the mechanism of cold spray deposition, the described influence of basic process parameters on the structure and properties of metal coatings. Performed analysis of chemical composition, structure, porosity, hardness and strength of AISI H13 steel coating on a high-alloy manganese steel substrate. The described dependence of the structure and properties of a given coating on the heat treatment regime.
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The mechanical properties of fiber reinforcement laminates
Jílek, Jan ; Němec, Karel (referee) ; Válka, Libor (advisor)
This bachelor's thesis summarizes the current findings in the area of evaluation of mechanical properties of fibre reinforcement laminates. In the thesis an algorithm for acquiring material characteristics of laminate by calculation is introduced, the results are tested by tensile stress. Among the calculated and experimental values of material characteristics only a small difference was found. The effect of temperature on stiffening of laminate on mechanical properties is studied.
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Microstructural stability of austenitic steels during fatigue loading
Kudelka, Martin ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
This diploma thesis studies the structure of selected austenitic stainless steels which were fatigued at room and depressed temperatures. The theoretical part is divided into three parts. The first one defines the austenitic stainless steels with accent to their chemical composition and microstructure. Second part is dedicated to deformation-induced martensite formation. The third part shows the mechanisms and stages of damage due to cyclic straining. The experimental part is focused especially on the observing of microstructural changes by methods of colour metallography and their relation to stress-strain response of material under selected conditions of fatigue loading. Series of samples of 304 and 316L steels were prepared by colour etching and their microstructures were documented using optical microscopy. Then the semi-quantitative measurements of presence and morphology of deformation-induced martensite were done and the results were discussed and correlated with fatigue damage level.
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Prediction of the fracture toughness temperature dependence
Václavík, Martin ; Pantělejev, Libor (referee) ; Válka, Libor (advisor)
The thesis is focused on the prediction of the fracture toughness temperature dependence through a universal curve of fracture toughness (also known as the master curve). To determine the parameters of the universal curve of fracture toughness, values acquired from the measurement results of fracture toughness and tensile tests of structural steel P91 are used. The theoretical part is based on a summary of the relevant information from the field of fracture mechanics and brittle-ductile fracture behavior of steels that are important for the understanding of fracture-strain response of materials depending on load conditions. The experimental part of the thesis contains the results from practical measurements and analyses, which were used for determining the parameters of a universal curve of fracture toughness as well as for the evaluation of fracture behavior and description of the impact of structural parameters on this behavior in case of steel P91.
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