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Creep Behaviour of Aluminium after Severe Plastic Deformation (ECAP)
Král, Petr ; Dvořák, Jiří ; Svoboda, Milan ; Sklenička, Václav
In this work the behaviour of ECAP aluminium with different number of passes at the creep tests was studied. The data indicated that an increase fraction of high angle boundaries has a strong effect on the creep properties of ECAP aluminium which can be explained by extensive grain boundary sliding contributing to the total creep deformation. However, the samples of ECAP aluminium with the identical number of ECAP passes showed significant differences of creep properties. The observed scatter in the creep behaviour is probably a direct consequence of different microstructures in the as-pressed state after ECAP.
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Influence of Microstructure Changes on the Mechanical Behaviour of Aluminium Processed by ECAP Method
Král, Petr ; Dvořák, Jiří ; Svoboda, Milan ; Sklenička, Václav
Extremely coarse – grained aluminium (99.99 %) was subjected to severe plastic deformation (Equal-Channel Angular Pressing) at room temperature. The properties of the ECAP material may considerably differ from properties of material with a standard coarse grain size. The largest changes of microstructure take place during the first four ECAP passes. Thus, the microstructure after twelve passes consists of roughly equiaxed grains (~m) with high fraction of high angle boundaries (~70%). In this work the behaviour of ECAP material with different number of passes at the tensile and creep tests has been studied. It is shown that ECAP aluminum provides a significant increase of the ultimate strength, however, there is low strain hardening during tensile deformation. The creep resistance of aluminum increased considerably already after one ECAP pass. However, repetitive ECAP pressing lead to a noticeable degrease in the creep properties. ECAP microstructure was examined in terms of the inhomogeneity. The results indicate that an inhomogeneity of the ECAP microstructure may influence the creep behaviour of the ECAP material.
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Propagation of inclined cracks to the interface of ceramic laminates
Novotná, Lenka ; Trunec, Martin (referee) ; Chlup, Zdeněk (advisor)
Composite materials with laminated structure provide advantages which are utilised during component design. Low density, temperature and chemical stability are the profitable properties predetermining application of ceramic laminates. The main obstacle for wide spread of ceramic materials is their inherent brittleness. Therefore, in this thesis, the crack propagation in ceramics laminates has been extensively studied. Laminated structures with various volume fractions of components (alumina and zirconia) were prepared by electrophoretic deposition. Evaluation of crack propagation through the interface and determination of basic mechanical properties was conducted on the basis of extensive literature search. Crack deflection originated in both presence of internal stresses and differences in elastic modulus during the crack interface passing was monitored. A special type of specimen geometry was employed with the aim to set arbitrary angle between crack and interface. It was experimentally found that the degree of crack deflection is dependent on entering angle and volume fraction of components. Higher crack deflection was already found in the bulk of the test piece comparing to the test piece surface. The 3D fracture surface reconstruction generated using laser confocal microscopy was used in this detailed crack propagation study. Further basic elastic and strength characteristics of laminates were determined and compared to those obtained from monolithic materials. The validity of the mix rule for elastic characteristics was confirmed by comparing of elastics modulus. The most reliable method for elastic modulus determination was marked the dynamic resonance method due to low scatter and consistency in measurement. The flexural strength of all laminates tends to be close to the flexural strength of the weakest component. Therefore the mix rule is not applicable for flexural strength estimation on the contrary of elastic characteristics. The change of component volume fraction leads only to change of flexural strength scatter. Thanks to gained knowledge about crack propagation and basic characteristic determination will be possible to design ceramic laminates more efficiently for given needs of application.
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Kritérium stability bi-materiálového vrubu se dvěma singularitami
Klusák, Jan
Interfaces with a step change of material properties occur often in technical constructions. In combination with a sharp notch it usually leads to singular stress distribution in a vicinity of such a wedge. The existence of two singularities seems to be the main problem within study of this stress concentrator. The other problem is that each singularity does not correspond to particular mode of loading. The presented contribution studies stress distribution in a bi-material wedge vicinity and shows a method of solution of the problems in case of existence of multiple stress singularity
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The structural and the fundamental mechanical properties of intermatallics on the base of TiAl
Krahula, Karel ; Dlouhý, Ivo
Gamma TiAl alloys are emerging as a pervasive structural material. Remarkable progresses have been made through refining lamellar microstructure and grains, microalloying, chemistry modification, process development and/or their combination. The main thrust was to enhance resistance to creep deformation, oxidation and high cycle fatigue deformation/failure. Less or even no knowledge have been obtained in the field of the intermetalics fracture at uniaxial or bending loading, there are missing data about their behaviour at the presence of cracks and other defects. The reason is simply in the other properties that are key from application point of view. Due to their brittleness at temperature close to room temperature the investigation of the intermetalics fracture is complicated but promissible provided it bring ideas for the further development of the alloying and microstructure. The paper is focused on the first steps in this field.
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Rheological properties of binders
Hotař, Petr ; Fišer,, Jiří (referee) ; Kudrna, Jan (advisor)
The comparison of rheological properties (complex shear modulus and phase angle and dynamic viscosity) of four paving bitumens and two polymer modified bitumens is performed in this diploma thesis. Furthermore, the empirical tests (needle penetration and softening point) were determined on these binders. Effect of asphalt binders aging was modeled using RTFOT test and modified RTFOT test (3 x RTFOT).
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Proposal for a stove fire
Štelcl, Otakar ; Skála, Zdeněk (referee) ; Baláš, Marek (advisor)
Abstract The diploma thesis is divided into five main parts. First part deals with wood as a firing in term of its composition, emissions of carbon dioxide and its properties. The second part describes the calculation of a stove fire, especially stoichiometry of firing, temperature of uncooled flame and area of combustion chamber. The third part focuses on the proposal for a stove fire in connection with comparative criteria of the fireplace, shape of the combustion chamber and the tertiary air jet. The fifth part describes a manufacturing of the stove fire in the work-room at VUT Brno. The major part of the diploma work pays attention to the measuring of stove fire parameters for the effectivity calculation, measuring section of combustion gas and measurement evaluation with stove fire constructional modifications
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