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Study of cooperative dislocation phenomena in solids by the acoustic emission technique
Knapek, Michal ; Chmelík, František (advisor) ; Haušild, Petr (referee) ; Landa, Michal (referee)
Title: Study of cooperative dislocation phenomena in solids by the acoustic emis- sion technique Author: Michal KNAPEK Department: Department of Physics of Materials Supervisor: doc. RNDr. František Chmelík, CSc., Department of Physics of Materials Abstract: Plastic deformation of micron-scale crystalline materials differs con- siderably from bulk specimens, as it is characterized by random strain bursts. Three categories of metallic samples were investigated in this thesis: micron- scale copper micropillars with varied geometries, submillimeter-scale aluminum microwires, and aluminum and aluminum-magnesium salt-replicated foams. Very precise fabrication methods and sensitive measurement set-ups consisting of uni- axial compression and tensile tests with concurrent acoustic emission (AE) record- ing were developed. These fine methods allowed for investigations of effects re- lated to plastic deformation at micrometer scales, i.e. the dislocation dynamics associated with the stress drops. Size effects in plastic deformation, as well as clear correlations between the stress drops and the AE events, were found in mi- crosamples, confirming that dislocation avalanches are indeed responsible for the stochastic character of deformation processes also at microscales. Open-cell pure aluminum and aluminum-magnesium...
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Mechanical and thermophysical properties of illite-based ceramic materials.
Kušnír, Jakub ; Knapek, Michal (advisor) ; Chmelík, František (referee)
Title: Mechanical and thermophysical properties of illite-based ceramic materials. Author: Jakub Kušnír Department: Department of Physics of Materials Supervisor: RNDr. Michal Knapek, Ph.D, Department of Physics of Materials Abstract: This work examines high purity illite-based ceramic material (illite) with varying porosity, illite with fly-ash addition and textured illite- and kaolin-based ceramics. Investigated illitic clay originated from the Tokaj region in Hungary and contained 84 wt.% of illite. Kaolinitic clay (Sedlecký Kaolin Inc.) contained 88-94 wt.% of kaolinite. Samples were prepared using different heating regimes based on the type of material, with maximum firing temperature of 1100 řC. The porosity was controlled by adding charcoal powder to the green body before firing. Fly-ash waste from the combustion of powdered oil shale from Estonia was used as another additive. The microstructure of samples was analyzed by scanning electron microscopy. Mechanical properties were studied by compression tests with concurrent application of advanced investigation methods: Acoustic emission (AE) and Digital image correlation. By means of thermal analyses and AE we also investigated the frost resistance of samples with porosity created by charcoal combustion. Keywords: illite; kaolinite; ceramics;...
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Study of cooperative dislocation phenomena in solids by the acoustic emission technique
Knapek, Michal ; Chmelík, František (advisor)
Title: Study of cooperative dislocation phenomena in solids by the acoustic emis- sion technique Author: Michal KNAPEK Department: Department of Physics of Materials Supervisor: doc. RNDr. František Chmelík, CSc., Department of Physics of Materials Abstract: Plastic deformation of micron-scale crystalline materials differs con- siderably from bulk specimens, as it is characterized by random strain bursts. Three categories of metallic samples were investigated in this thesis: micron- scale copper micropillars with varied geometries, submillimeter-scale aluminum microwires, and aluminum and aluminum-magnesium salt-replicated foams. Very precise fabrication methods and sensitive measurement set-ups consisting of uni- axial compression and tensile tests with concurrent acoustic emission (AE) record- ing were developed. These fine methods allowed for investigations of effects re- lated to plastic deformation at micrometer scales, i.e. the dislocation dynamics associated with the stress drops. Size effects in plastic deformation, as well as clear correlations between the stress drops and the AE events, were found in mi- crosamples, confirming that dislocation avalanches are indeed responsible for the stochastic character of deformation processes also at microscales. Open-cell pure aluminum and aluminum-magnesium...
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Mechanical and thermophysical properties of illite-based ceramic materials.
Kušnír, Jakub ; Knapek, Michal (advisor) ; Chmelík, František (referee)
Title: Mechanical and thermophysical properties of illite-based ceramic materials. Author: Jakub Kušnír Department: Department of Physics of Materials Supervisor: RNDr. Michal Knapek, Ph.D, Department of Physics of Materials Abstract: This work examines high purity illite-based ceramic material (illite) with varying porosity, illite with fly-ash addition and textured illite- and kaolin-based ceramics. Investigated illitic clay originated from the Tokaj region in Hungary and contained 84 wt.% of illite. Kaolinitic clay (Sedlecký Kaolin Inc.) contained 88-94 wt.% of kaolinite. Samples were prepared using different heating regimes based on the type of material, with maximum firing temperature of 1100 řC. The porosity was controlled by adding charcoal powder to the green body before firing. Fly-ash waste from the combustion of powdered oil shale from Estonia was used as another additive. The microstructure of samples was analyzed by scanning electron microscopy. Mechanical properties were studied by compression tests with concurrent application of advanced investigation methods: Acoustic emission (AE) and Digital image correlation. By means of thermal analyses and AE we also investigated the frost resistance of samples with porosity created by charcoal combustion. Keywords: illite; kaolinite; ceramics;...
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Study of deformation mechanisms in extruded magnesium alloys containing neodymium and yttrium
Hojnoš, Peter ; Minárik, Peter (advisor) ; Chmelík, František (referee)
Submitted work shows results of the investigation of ternary (WN43) and two binary magnesium alloys containing neodymium (2Nd) and yttrium (4Y) extruded at two different extrusion rates (2 and 5 mm/s). Microstructure of the investigated samples was analysed by light microscope. Additionally, texture of all samples was measured by X-ray diffraction. Mechanical properties were studied by compression deformation tests with two different deformation directions with respect to the processing direction. Acoustic emission was recorded during the deformation tests in order to correlate deformation behaviour with the micros- tructure. Analysis of the acoustic emission helps to identify deformation micro- mechanisms acting during the mechanical straining. Additionally, effect of sample size and deformation rate on the deformation mechanisms was investigated. 1
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Study of cooperative dislocation phenomena in solids by the acoustic emission technique
Knapek, Michal ; Chmelík, František (advisor) ; Haušild, Petr (referee) ; Landa, Michal (referee)
Title: Study of cooperative dislocation phenomena in solids by the acoustic emis- sion technique Author: Michal KNAPEK Department: Department of Physics of Materials Supervisor: doc. RNDr. František Chmelík, CSc., Department of Physics of Materials Abstract: Plastic deformation of micron-scale crystalline materials differs con- siderably from bulk specimens, as it is characterized by random strain bursts. Three categories of metallic samples were investigated in this thesis: micron- scale copper micropillars with varied geometries, submillimeter-scale aluminum microwires, and aluminum and aluminum-magnesium salt-replicated foams. Very precise fabrication methods and sensitive measurement set-ups consisting of uni- axial compression and tensile tests with concurrent acoustic emission (AE) record- ing were developed. These fine methods allowed for investigations of effects re- lated to plastic deformation at micrometer scales, i.e. the dislocation dynamics associated with the stress drops. Size effects in plastic deformation, as well as clear correlations between the stress drops and the AE events, were found in mi- crosamples, confirming that dislocation avalanches are indeed responsible for the stochastic character of deformation processes also at microscales. Open-cell pure aluminum and aluminum-magnesium...
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Study of cooperative dislocation phenomena in solids by the acoustic emission technique
Knapek, Michal ; Chmelík, František (advisor)
Title: Study of cooperative dislocation phenomena in solids by the acoustic emis- sion technique Author: Michal KNAPEK Department: Department of Physics of Materials Supervisor: doc. RNDr. František Chmelík, CSc., Department of Physics of Materials Abstract: Plastic deformation of micron-scale crystalline materials differs con- siderably from bulk specimens, as it is characterized by random strain bursts. Three categories of metallic samples were investigated in this thesis: micron- scale copper micropillars with varied geometries, submillimeter-scale aluminum microwires, and aluminum and aluminum-magnesium salt-replicated foams. Very precise fabrication methods and sensitive measurement set-ups consisting of uni- axial compression and tensile tests with concurrent acoustic emission (AE) record- ing were developed. These fine methods allowed for investigations of effects re- lated to plastic deformation at micrometer scales, i.e. the dislocation dynamics associated with the stress drops. Size effects in plastic deformation, as well as clear correlations between the stress drops and the AE events, were found in mi- crosamples, confirming that dislocation avalanches are indeed responsible for the stochastic character of deformation processes also at microscales. Open-cell pure aluminum and aluminum-magnesium...
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