|
|
Transformace dynamické odolnosti nerezových ocelí vlivem strukturní nehomogenity
Dobrovolný, Pavel
This diploma thesis: Transformation of the dynamic resistance of stainless steels due to structural inhomogeneity deals with the effects of corrosive damage on fatigue properties of stainless steels. The theoretical part deals with general principles of creation and chemical reactions, the factors affecting their speed, as well as, fatigue properties of materials (formation of cracks, stages of high cycles fatigue, fatigue slip zone etc.) and description of the method of non destructive testing the acoustic emission. The practical part describes executed experiment which focuses on comparing the results of fatigue tests between the standards and thermal and corrosion exposed samples. The actual measurements supplement microscopic images of the fracture surfaces and the records acoustic emission during measurements of some samples.
|
|
|
Performace rychlosti martenzitické transformace při snímání silových akustických pulsů
Mazal, Aleš
Thesis topic: Performance speeds martensitic transformation when shooting power acoustic pulses deals with the thermal processing of steel when recording acoustic emission. The theoretical part deals with the hot gas transition, martensitic transformation, refining steel, and basic information about the acoustic emission. The practical part consisted of sensing acoustic emission during hardening steels in water and in oil, followed by detecting the hardness in different locations of the sample. Evaluation was carried out using a hardness test, metallographic images and records acoustic emission obtained during hardening.
|
|
|
Analýza CMT svarových spojů
Doležel, Radek
Thesis on Analysis CMT welded joints simply describes welding process and CMT welding methods. Individual chapters deal with the emerging defects in the weld-ed materials and inform readers with selected non-destructive methods. An important chapter is the CMT welding process at the selected three pairs of material CMT and CMT welding evaluate the advantages for heterogeneous materials (aluminium and steel).
|
|
|
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.
|
|
|
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.
|
|
|
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...
|
|
|
Characterization of migmatite fracturing using ultrasonic methods
Petružálek, Matěj ; Vilhelm, Jan (advisor) ; Vavryčuk, Václav (referee) ; Koktavý, Pavel (referee)
Submitted PHD thesis is focused on fracturing process of migmatite, which is a low porosity anisotropic rock. Migmatite, from a locality Skalka, was chosen as a suitable experimental material, namely due to its macroscopically visible, plane-parallel structure (foliation). The fracturing was studied by means of uniaxial loading experiments on cylindrical samples with different dip of migmatite foliation: 13ř (subhorizontal), 81ř (subvertical) and oblique (47ř and 67ř). The net of eight piezoceramic transducers was employed for ultrasonic sounding (US) measurement and acoustic emission (AE) monitoring during the loading experiments. Realized study of migmatite fracturing is based on the interpretation of both mentioned ultrasonic methods. Part of this work was a software development, including its testing for processing and interpretation of measured AE and US data. Methodical part of the thesis consists of: development and testing of algorithms for automatic P wave arrival detection; introduction of anisotropic velocity model to describe magnitude and orientation of velocity anisotropy, as well as to localize AE events in anisotropic velocity field; determination of crack initiation stress using first arrival amplitude of US. Based on the interpretation of AE and US data, there was found a...
|
|
|
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...
|
|
|
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)
|
|
|
Study of mechanical and thermal properties of nanoparticle-reinforced composites
Németh, Gergely ; Mathis, Kristián (advisor) ; Lukáč, Pavel (referee)
Title: Study of mechanical and thermal properties of composites reinforced by nanoparticles Author: Gergely Németh Department: Department of Physics of Materials Supervisor: RNDr. Kristián Máthis, Ph.D. Abstract: In the present work the deformation behavior of magnesium-based alloy AZ31 reinforced by SiC nanoparticles which was produced by horizontal continual casting is studied. Tension tests in the room temperature, compression tests in the temperature range of 20řC-300řC have been preformed. Samples was with two different orientation. Deformation strain rate was 10-3 s-1 . Simultaneously, the acoustic emission is recorded and studied. The mechanisms of plastic deformation of material are discussed mainly in term of mechanical twinning. Dependence of deformation behavior in compression on temperature is analyzed. The microstructure of original and deformed material is also studied. Keywords: magnesium alloys, composit material, mechanical twinning, metals with hexagonal structures.
|
guest ::
