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The Influence of Multilayer Composite Interface on Crack Propagation Direction
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel
The paper deals with crack propagation in multilayer composites. A substantial number of experimentally based works have indicated the changes in crack propagation direction on multilayer composite interfaces. Changes of this kind are mostly desirable for composite technical life extension. Crack direction modification in the composite interface is investigated through a numerical simulation of this problem. For determination of the consequent propagation direction the minimal strain energy density criterion is employed. The ascertained propagation direction of the crack in the multilayer composite is compared with experimental results.
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Detection of Eccentricity and Broken Rotor Bar Faults by Means of Monitoring of Current and Magnetic Flux Density Spectrums
Ishkova, I.
In this paper, faults detection and classification using motor current signature analysis (MCSA) and monitoring of magnetic flux density in air-gap of the machine is presented. A series of simulations using the models of three phase cage induction motor performed in different fault condition, such as static, dynamic and mixed eccentricity and broken rotor bars. Designed models were implemented with the help of finite element method to provide data that makes it possible to diagnose presence of any type of fault, as well as to analyze obtained and calculated results. Models were designed on the basis of characteristics and parameters of real motor. The results are illustrated in the form of graphs that makes visible illustration for effectiveness of the used diagnosis method.
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Vysokoteplotní tahové vlastnosti kvazikrystalické Al slitiny
Chlup, Zdeněk ; Dlouhý, Ivo
Low density, sufficient strength and high temperature resistance are the basic requirements for materials used for aerospace and automotive applications. The nanostructured aluminium alloy reinforced by quasi-crystals prepared by powder metallurgy supposes to be a good alternative to currently used alloys. The aim of this paper is to describe high temperature tensile properties of nanostructured quasi-crystalline aluminium alloy including the changes in fracture mechanism at different strain rates and temperatures. High temperature behaviour was assessed by tensile tests of cylindrical testpieces at temperatures ranging from 20C to 550C. Two strain rates 2.7x10 -4 and 1.1s -1 were applied over the whole temperature range of interest. Fractographic analysis was used to describe fracture mechanism and its changes with increasing temperature and loading rate. The material under investigation proved the potential for high temperature applications
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Methods of measurement of bone density
Konvalinka, Jan ; Valášek, Jiří (referee) ; Marcián, Petr (advisor)
This bachelor's thesis focuses on methods for measuring bone density and consequences of changes in bone density on biomechanical properties of bone tissue. In first part are described methods of bone densitometry, especially radiological methods, which are currently most widely used. Second part focuses on measuring bone density from CT images (hog femur bone, healthy and damaged human femur bone and lumbar vertebra) using software ROI Analysis. Third part discusses influence of changes in bone density on strain-stress quantities of trabecular bone. For the assessment was created 2D computational model of hip using FEM.
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Modification of polyurethane by biodegradable poly(hydroxybutyrate)
Kupka, Vojtěch ; Žídek, Jan (referee) ; Vojtová, Lucy (advisor)
Cílem předložené bakalářské práce byla syntéza elastomerního polyuretanu plněného biodegradabilním polyhydroxybutyrátem. Vzorky byly podrobeny analýze morfologie pomocí rastrovací elektronové mikroskopie, mechanické vlastnosti byly testovány jednoosou tahovou zkouškou. Práce se taktéž zabývá předpovědí mechanických vlastností na základě teorií kaučukové elasticity. Bylo zjištěno, že výsledný materiál je částicový kompozit, kde se vzrůstajícím hmotnostním obsahem plniva v materiálu vzrůstá modul pružnosti. Predikce tahových křivek pomocí softwaru SEC.exe ukazovala pro reálný průběh křivky nereálné hodnoty hustot polymerních řetězců. U modelů, které vykazovaly reálné hodnoty hustot, byly naopak hodnoty napětí vyšší, než ve skutečnosti naměřené.
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Characterisation of InAs/GaAs quantum dots by high resolution transmission electron microscopy
Zíková, Markéta ; Hospodková, Alice ; Pangrác, Jiří ; Hulicius, Eduard ; Komninou, Ph. ; Kioseoglou, J.
The InAs/GaAs quantum dots (QDs) covered by GaAsSb strain reducing layer (SRL) have suitable properties for various applications. The GaAsSb SRL covering InAs QDs is used to improve the structure growth and the final parameters like QD density, QD size or photoluminesence. To obtain high-quality structure with required properties, the structure growth and final structure have to be deeply studied. Since the QDs and SRL system is surrounded by GaAs, the high resolution transmission electron microscopy (HRTEM) measurement was used to reveal the real material arrangement in a prepared sample. In this work we will discuss the results of following HRTEM measurements: flatness and thickness of prepared layers, QD size, atomic arrangement and composition of GaAsSb layer.
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Evaluation of effectiveness of destress coal blasting fro stress release
Koníček, Petr ; Przeczek, A.
Destress blasting in the coal seam are important active rockbursts measures in conditions of Czech part of the Upper Silesian Coal Basin. Destress coal blasting involves regularly setting off carefully tailored blasts in the fractured coal immediately ahead of a mining face, so as to encourage slip on pre-existing fractures, in order not to allow the accumulation of high strain energy density in the rock mass. In some cases high stress in coal seams (or surrounded rocks) can be reduced. In cases that we demands high stress release we evaluates effect of stress release. Evaluation of stress release is carried out the same procedure without difference between destress blasting in rock and in the coal seam. Paper describes the first analysis of destress blasting in coal seams realised in period 2008 – 2010 (source of seismological databases, about 1200 data). The result of analysis shows of necessity of separate system of stress release evaluation by destress blasting in coal seams and rocks.
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FEM modeling of thermo-mechanical interaction in rubber block
Pešek, Luděk ; Půst, Ladislav ; Šulc, Petr
The FEMLAB code based on weak formulation of PDE’s problem was used at a solution of feedback thermo-mechanical interaction in damping bodies by finite element method. In our approach structural motion and heat conduction equations are solved interactively as time dependent problems. The conservative energy law, i.e. equality of heat energy density and dissipation energy density, realizes the coupling between the equations. The dissipation energy density is computed according to the assumed damping model. In the contribution the results, such as temperature versus strain distribution, of thermo-mechanical processes in case of a plane strain deformation under static compression and cyclic dynamic loading concerning mechanical energy lost modeled as proportional damping, heat generation, heat transfer between rubber and outer steel parts, cooling problem and changing stiffness and damping coef.
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