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Determination of thermal conductivity anisotropy of polymeric heatsinks for electronics
Brachna, Róbert ; Kůdelová, Tereza (referee) ; Komínek, Jan (advisor)
The master's thesis focuses on creating a numerical model of a polymeric heat sink with emphasis on its significant thermal conductivity anisotropy. This anisotropy is caused by highly thermally conductive graphite filler. Its final orientation is given by the melt flow inside the mould cavity during injection molding. The numerical model is created on the basis of a heat sink prototype subjected to experimental measurements, whose physical conditions are reliably replicated by the model. The determination of anisotropy is divided into two parts. The qualitative part is based on the fracture analysis of the heat sink prototype and determines the principal directions of the conductivity tensor in individual sections of the geometry. The computation of principal conductivities falls into the quantitative part, in which this task is formulated as an inverse heat conduction problem. The input data for the proposed task are experimentally obtained temperatures at different places of the geometry. The values of principal conductivities are optimized to minimize the difference between the measured and simulated temperatures.
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Laser-induced surface acoustic waves for thin film characterization
Kudělka, R. ; Václavek, L. ; Tomáštík, Jan ; Malecová, S. ; Čtvrtlík, R.
Knowledge of mechanical properties of thin films is essential for most of their applications.However, their determination can be problematic for very thin films. LAW (Laser-induced acousticwaves) is a combined acousto-optic method capable of measuring films with thickness from fewnanometers. It utilizes ultrasound surface waves which are excited via short laser pulses and detectedby a PVDF foil. Properties such as Young’s modulus, Poisson’s ratio and density of both the film andthe substrate as well as film thickness can be explored.Results from the LAW method are successfullycompared with nanoindentation for Young’s modulus evaluation and with optical method for filmthickness evaluation and also with literature data. Application of LAW for anisotropy mapping ofmaterials with cubic crystallographic lattice is also demonstrated
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The use of small punch tests for materials with a higher level of structural inhomogeneity
Gordiak, Michal ; Řehořek, Lukáš (referee) ; Válka, Libor (advisor)
Master's thesis deals with evaluating applicability of correlation relationships between material characteristics determined by Small Punch Test and standard tensile test for material AlSi7Mg0,6 manufactured by casting and technology SLM. Results of Small Punch Tests are correlated with yield strength, tensile strength, elongation, and Young's modulus of elasticity. For each material characteristic various correlation methods are compared, while for each method corresponding coefficients are determined. Consequently, the applicability of individual methods is evaluated by substituting coefficients determined by various studies. Primarily analyzed are correlation methods for which future normalization is expected. The results of master's thesis show that structural inhomogeneity caused by SLM process does not result in high inaccuracies in determining material characteristics. Larger impact on material characteristics has high porosity, which was identified in cast material and led to significant deviations in evaluating tensile strength and elongation.
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Modeling of anisotropic viscoelastic fluids
Šípka, Martin ; Tůma, Karel (advisor) ; Průša, Vít (referee)
In this thesis, we aim to create a framework for the derivation of thermodynamically consistent anisotropic viscoelastic models. As an example we propose simple models extending the isotropic Oldroyd-B and Giesekus models to illustrate the models' behavior and the process of finding the correct equations. We show what behavior in sheer we can expect and continue with a 3D simulation inspired by the experiment on a real liquid crystal mixture. Finally, we compare the simulation and the experiment to find similarities and possible further research topics.
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Anisotropy of Turbulent Flow around an Airfoil
Uruba, Václav ; Procházka, Pavel P. ; Skála, Vladislav
The flow around an airfoil is analyzed from the point of view turbulence anisotropy assessment. The turbulent flow-field in the vicinity of an airfoil is populated by vortices, in some locations they tend to regularity in orientation, i.e. to anisotropy. However in the wake behind the plate as well as in the core of the boundary layer on the plate suction side the turbulence is close to isotropic state.
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Magnetism in non-centrosymmetric uranium compound: UIrSi3
Valenta, Jaroslav ; Prchal, Jiří (advisor) ; Halevy, Itzhak (referee) ; Isnard, Olivier (referee)
Title: Magnetism in the non-centrosymmetric uranium compound: UIrSi3 Author: RNDr. Jaroslav Valenta Department: Department of Condensed Matter Physics Supervisor of the doctoral thesis: RNDr. Jiří Prchal, Ph.D., DCMP Abstract: The study presented in this thesis is focused on UIrSi3 which is one of two known uranium compounds that crystallize in a non-centrosymmetric structure. This first study of UIrSi3 in single-crystalline form confirms antiferromagnetic order below TN = 41.7 K and reveals strong uniaxial anisotropy. The antiferromagnetic order is suppressed by application of a magnetic field along the c axis (0HC = 7.3 T at 2 K). In contrast, application of a magnetic field up to 14 T along the a axis gives paramagnetic response. The high TN, contrasting with the low 0HC, together with the opposite signs of the paramagnetic Curie temperatures of the a-axis and c-axis paramagnetic susceptibility indicate a competition between antiferromagnetic and ferromagnetic interactions. The first-order metamagnetic transition at HC shows asymmetric hysteresis which reflects a complex antiferromagnetic ground state. With increasing temperature, the hysteresis becomes gradually smaller and vanishes at 28 K where the first-order transition changes to second-order transition which remains up to TN. The point where the...
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Manufacturing of a Component by Using Hydroforming Technology and Its Optimization
Harant, Martin ; Peterková, Eva (referee) ; Řiháček, Jan (advisor)
The project deals with analysis and optimization of the geometry of the stamped part produced by the pillow hydroforming. The blank consists of two sheets of steel DC01, which is welded by laser beam. The forming process can cause excessive thinning and cracking of the part. By evaluation of mechanical tests is created material model, which is the basis for numerical simulation created in software PAM-STAMP. The outputs are analysis which provide information about critical points, failure pressure, limiting deformations and prediction of springback. Validity of the numerical simulation is verified by comparison with the experimentally obtained data. The comparative criterions are the failure pressure and the material thickness at various locations. Based on the results of the numerical simulation, the optimization of the geometry is created. The optimization uses different values of radius at the crack point.
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Analysis of direction dispersion of collagen fibers in soft tissues
Sádovská, Terézia ; Lisický, Ondřej (referee) ; Turčanová, Michaela (advisor)
The bachelor thesis deals with the directional distribution of collagen fibres in soft tissues especially in arteries and tendons. The first part gives basic information about anatomy of human vascular system, particulary structure of the arteries. There are explained polarization microscopy principle of materials exhibiting birefringence. Further is described relation between direction of density and mechanical properties expresses as modulus in tensile. In the next section, we will be defined stress in arterial wall using linear stregth and stiffness. In the last part of thesis will be observed dispertion of collagen fibres in tendon. This dispertion is described by circular distribution Von Mises. At the end is evaluated how dispertion of collagen fibres effects mechanical properties of arteries.
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