National Repository of Grey Literature 88 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Modernization of R-mat test stations
Papaj, Lukáš ; Dočkal, Aleš (referee) ; Mazal, Pavel (advisor)
The aim of the thesis is to reconstruct obsolete R-mat test stations, which are used for rolling contact fatigue tests of material, which are still of interest from industry. It was necessary to replace the original control electronics with a new industrial computer to allow use modern sensors and automate the entire test process. At the same time, the measurement was supplemented by an acoustic emission method, which can also record the development of damage. Design modifications have been made that allow the installation of all new sensors. The main method for evaluating the tests is vibrodiagnostics, which is supplemented by the acoustic emission method. With the help of several experiments, the shortcomings of the new control system were identified, some parameters were designed, and the main functionality of the modernized R-mat station was verified. According to the proposed parameters and the identified shortcomings, the control system was modified, and a script was created, which is used to evaluate the test. It is still possible to perform rolling contact fatigue tests of the material on the modernized equipment, and thanks to the modernization of the electronics, it is possible to test completely new methods of test evaluation.
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...
Effect of alloying elements and texture on plastic deformation of extruded magnesium alloys
Horváth, Klaudia ; Dobroň, Patrik (advisor)
This work is focused on the study of the relationship between microstructure, texture and deformation mechanisms in aluminum-free magnesium (Mg) alloys. Extruded alloys containing zirconium, zinc, manganese and neodymium (ZK10, MN11, ZN11) in a form of rectangular profiles were deformed at room temperature. Uniaxial tensile and compression tests were performed in the extrusion (ED), transversal (TD) and normal direction (ND). The concurrent acoustic emission (AE) measurement was used in order to study the collective dislocation dynamic and the nucleation of twins. The deformation texture was studied by X-ray diffraction on samples deformed in compression up to different stress levels.
Investigation of plastic deformation instabilities by the acoustic emission technique
Molnárová, Orsolya ; Dobroň, Patrik (advisor)
The influence of the strain rate and heat treatment on the occurrence of plastic instabilities in extruded AlSi1MgMn (6082) and cold rolled AlMg4.5Mn0.4 (5182) alloys was studied. The samples were uniaxially loaded at various strain rates and at room temperature (RT). The results are discussed using concurrent acoustic emission (AE) monitoring during mechanical testing and the AE parameters are correlated to the microstructure and to the stress- time curves. All samples exhibited the Portevin-Le Châtelier (PLC) effect of different types, dependently on the heat treatment and the applied strain rate. The occurrence of the PLC effect is manifested by burst AE signals with high amplitudes. Statistical analysis of the AE signals has shown the power-law probability distribution.
Study of deformation processes in hexagonal materials
Čapek, Jan
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation. Powered by TCPDF (www.tcpdf.org)
Mechanical properties of a novel magnesium WN43 alloy prepared by spark plasma sintering
Greš, Adam ; Knapek, Michal (advisor) ; Dobroň, Patrik (referee)
Title: Mechanical properties of a novel magnesium WN43 alloy prepared by spark plasma sintering Author: Adam Greš Department: Department of Physics of Materials Supervisor: RNDr. Michal Knapek, Ph.D., Department of Physics of Materials Abstract: Properties such as low modulus of elasticity, low toxicity, and biode- gradability make magnesium alloys interesting candidates for medical applicati- ons. To avoid potentially harmful effects of rare earth mischmetal present in the commercial WE43 alloys, it has been replaced in this study with pure neody- mium, which exhibits lower toxicity. To achieve high control over the material microstructure, it was prepared using the spark plasma sintering technique. This study focuses on exploring the mechanical properties of the novel WN43 alloy using compression and tensile testing accompanied by the acoustic emission tech- nique. Ultimate compressive strength and ductility were observed to improve significantly with higher sintering temperatures. In order to obtain better insi- ghts into microscopic aspects of the deformation mechanisms, EBSD images of the samples were taken at multiple points during deformation. It was shown that around the yield point twin nucleation produces strong acoustic emission signal, while later stages of deformation are mostly accommodated by...
Využití akustické emise při hodnocení procesu obrábění
Dostál, Jiří
The thesis deals with the application of acoustic emission system to the machining process. The thesis describes the gist of the machining, the influence of the cutting conditions on the machining process, and attention is also focused to the used tooling materials and creation of sliver. Another part deals with acoustic emission, its basic characteristics and areas of its use. In the experimental part, is determine the measurement objective, is described there methodology of the measurement and the data obtained from the measurement is then evaluated.
Stanovení optimálních řezných podmínek na základě vizulizace řezných odporů
Čupa, Jan
The thesis named Determination of optimum cutting conditions based on the visualization of cutting resistances is focused on the determination of optimum cutting conditions by the method of non-destructive testing - acoustic emission. Thesis specifically deals with the detection of cutting tool wear during continuous observation of machining process. The theoretical part of thesis starts with the theory of machining and wear mechanisms of cutting tools. Considerable attention has been paid to compilation from cutting force measurement. Final chapter of this part describes method of acoustic emission. Practical part of the thesis describes preparation and methodics of the experimental measurement. Next there is described measurement process with sharp and worn cutting tool. End of the thesis evaluates measurement results and also suggests practical application of the obtained knowledge.
Verifikace souběžného měření odezvy plastické deformace
Pištora, Jan
Goal of this diploma work is to practically test method of concurrent hardness and acoustic emission measurement related to theyr correlation depending on material.
Monitoring degradačních vlastností karbonu
Němeček, Václav
In the diploma thesis there was made an attempt to compare the samples of carbon fiber composite materials (carbon). The teoretical part presents knowledge of the composition of composite material. Next, there is described the production and possible use of carbon composite materials in various technological branches. In the practical part the thesis focuses on the testing of composite materials made of carbon fiber with different orientation and weights of fibers. There is performed a tensile test and simultaneous monitoring of the course of the tensile test by acoustic emission. Finally, the statistical processing of the measured values occurs.

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