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Interaction between TiAl melt and coated oxide refractories
Dočekalová, Kateřina ; Dlouhý, Antonín ; Zemčík, L. ; Fiala, J.
The present study focuses on reactions between ceramic crucibles and molten TiAl intermetallics. Coating strategies are investigated that exhibit a potential in slowing down the decomposition of the crucible wall. Uncoated crucibles (system TiAl melt - Al2O3 crucible) and crucibles with the coat (system TiAl melt - CaO coat - Al2O3 crucible) were used in melting and casting experiments. The reference state of the coated crucible before the melting trial was also investigated. Results of the SEM, EDAX and X-ray diffraction analysis contributed to the identification of the reaction zone and its chemical composition. The melt contamination with oxide inclusions results from the erosion process in which individual components of the melt diffuse along grain boundaries of the refractory and activate chemical reactions that decompose the crucible wall. Assessment of thermodynamic parameters associated with the chemical reactions helped in identifying the nature of the erosion process.
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Design and stress analysis of temperature and force sensor in hot rolling process.
Nejedlý, Pavel ; Pohanka, Michal (referee) ; Horský, Jaroslav (advisor)
In the process of hot rolling is roll surface thermo-mechanically stressed. To define lifetime of roll or to increase it by change of thermal mode, temperatures and forces acting on this roll need to be known. For this purpose should be used sensors, that are placed near by surface of roll. Aim of the first part of diploma thesis is to debug 2D computing model (MKP) to achieve the match of temperature graphs with experimentally measured values, which was recorded by temperature sensors in real process of rolling. In the second part the same temperature boundary conditions are applied on 3D model, which is used to solve mechanical strength check of the temperature sensor. The last part of thesis is design and verification of mechanical strength of the designed force sensor. The used boundary conditions were acquired in Laboratory of heat transfer and flow. The computing system ANSYS 11 is used to design a model of geometry and numerical calculation. This diploma thesis will be used as donating solution for the granted project, which started in this year with Laboratory of heat transfer and flow partnership.
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Effect of the temperature-dependent viscosity on the laminar flow in the entrance region of a circular tube
Mík, Václav
An analytical-numerical model of the velocity and temperature field was created. The model was tested by comparison of the calculated temperatures of the wall in the region of the development of the velocity profile and the values obtained experimentally. The model was employed to monitor the effect of the temperature-dependent viscosity on the flow conditions in the entrance part of the tube. Liquids with various viscosities were used and the differences were evaluated between isothermal flow and flow during heating of the wall by a constant heat fluxes taking into consideration the temperature-dependent viscosity. The shapes of the isothermal and non-isothermal velocity profiles, the temperature profiles, the changes in the thickness of the hydrodynamic and temperature boundary layers and the changes in the velocity gradient at the wall for isothermal and non-isothermal flow were obtained in the region of development of the velocity profile. These data could be used to quantitatively evaluate the effect of the temperature-dependent viscosity on the flow and heat transfer in the entrance region of the tube.
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Motion Feedback of Man to the Monotonous Sittting Stress from the Point of View of the Th1 and PSIS 3D-kinematics and Pressure
Cerhová, Ivana ; Jelen, Karel (advisor) ; Tlapáková, Eva (referee)
Aim of the thesis: Description of the current feeling of dyscomfort in three different probands under standard conditions as well as the modalities to relieve this dyscomfort, it's objectivisation by means of two experimental analytical methods - the Footscan technology and Qualysis as well as the questionnaire method. Method: 1. questionnaire 2. Th1 and PSIS motion detection - QUALISYS technology 3. relative pressure forces detection on the man-seat-technology boundary FOOTSCAN + Panasonic digital video camera Results: our study brought useful information concerning the perception and ways of reaction to sitting discomfort from the point of view of subjective perception and objective parameters of discomfort detection - pressure distribution on the interaction boundary as well as the motion response analaysed in 3D. These parameters have been compared both intra- and interindividually. Key words: sitting, dyscomfort, objectivisation, motion feedback, pressure distribution
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Analýza rozdělení napětí pro trhlinu s vrcholem na rozhraní dvou materiálů
Náhlík, Luboš
The problem of arbitrarily oriented crack terminating at the boundary of two bonded materials is studied from the point of view of linear elastic fracture mechanics. The nature of the stress singularity for the crack terminating at the interface is different from 1/ square root of r and thus current fracture mechanics criteria cannot be adopted. The values of stress singularity exponent for selected ratio of elasticity modulus of both applied materials in dependency on orientation of crack and interface are calculated.
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Influence of grain orientation on threshold values of short fatigue cracks
Náhlík, Luboš ; Knésl, Zdeněk
The influence of a grain boundary on the propagation of a fatigue crack is studied. To this aim the grain boundary is considered as an interface between two different materials with their elastic constants depending on the orientation of the adjacent grains. The main goal is to estimate the threshold value of a microstructurally short fatigue crack propagating through the grain boundary. The corresponding threshold values are calculated as a function of material parameters of grains. Corresponding modelling have been performed by combination of analytical and numerical approach. For numerical calculations the finite element system ANSYS has been used. The model describes only one of many aspects of short fatigue crack behaviour and the results obtained contribute to a better understanding of microstuctural aspects of short fatigue crack growth.
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Boundary Conditions in the Roll Gap during Hot and Cold Rolling
Luks, Tomáš ; Pernis,, Rudolf (referee) ; Hajduk, Daniel (referee) ; Horský, Jaroslav (advisor)
Boundary conditions in the roll gap play an important role in modelling of rolling processes. In the roll gap we can observe the following: changes of rolling pressure, changes of relative velocity, influences of oxides and lubrication, etc. When taking into account all conditions mentioned above the determination of the boundary conditions is not trivial and extensive measurements are necessary. Therefore, this thesis is dealing with design of temperature and force sensors specified for the determination of friction coefficient and heat transfer coefficient in contact. The temperature sensor with an installed thermocouple measures subsurface temperature for a given depth; and then the inverse heat conduction task is used to compute temperature and heat flux on the surface. Several temperature sensors were designed and used for measuring in pilot mill and industrial rolling mill as well. The thermal responses of different sensors were compared in the numerical simulations. The inverse calculations were tested for various rolling conditions. A durability of the sensors was also studied in industrial rolling conditions. The contact stresses in the roll gap were measured by a pin, which was in direct contact with the rolled material. The forces on the top of the pin were measured by a three-axes piezoelectric force transducer and recalculated to the contact stress and friction coefficient. The sensor was implemented in a work roll and tested when rolling aluminium and steel slab for different rolling conditions. The results were compared with the integrative force sensor ROLLSURF.
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