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Porušování jemnozrnného cementového kompozitu v blízkosti rozhraní plniva a matrice
Vyhlídal, Michal ; Kabele,, Petr (referee) ; Profant, Tomáš (referee) ; Keršner, Zbyněk (advisor)
The Interfacial Transition Zone (ITZ) between the aggregate grain/reinforcement bar and the matrix is considered to be the weakest element in cementitious composites and is, according to some authors, directly responsible for the nonlinear (more precisely, quasi-brittle) behavior of the composites. The aim of this work is verification of the generally accepted paradigm of the weakest element by means of fracture experiments and corresponding numerical simulations. In the experimental part, in addition to traditional fracture tests, modern methods of 3D scanning, scanning electron microscopy, chemical analysis using an electron microprobe and nanoindentation were used. In the numerical part, models based on generalized linear elastic fracture mechanics as well as modern models intended for the simulation of cement composites, namely crack band model with smeared cracks and the Microplane model, were used. Based on the results, the numerical part was complemented by the Cohesive Zone Material model simulating the behavior of the interface. All results are discussed and put into context with already published work. The main conclusion of the work is that the properties of the ITZ do not have such an influence on the behavior of cement composites as the adhesion between the inclusion and the ITZ, i.e. the matrix.
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Ventilation and air conditioning of a car cabine
Viščor, Petr ; Hejčík, Jiří (referee) ; Fišer, Jan (advisor)
In this work are described kinds and functions of air-conditioning systems which are used in cars. Further is described heat transfer between car cabin and ambient environment and issue of reduction of air-conditioning energy consumption. Last part of the work contains numerical simulation made by the THESEUS-FE 2.1 software package. This simulation was done on a model of the Toyota Prius car and was focused on effect of glazing on a temperature of the air inside the car cabin during hot summer days.
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The Segregation in Ferrous Alloys when Casting Heavy Castings
Pernica, Vítězslav ; Čech, Jan (referee) ; Vodárek, Vlastimil (referee) ; Havlíček,, František (referee) ; Šenberger, Jaroslav (advisor)
This thesis is dedicated to the field of manufacture of heavy steel castings with resulting properties which are influenced by long solidification time. During the long solidification time a segregation process of additives in the steel occurs which results in numerous metallurgical defects. The work was intended to observe the macrosegregation effects in the wall of a heavy experimental steel casting respectively a part of a real superheavy casting intended for cement furnaces (weight 210 t). The steel casting for the research was manufactured in the joint-stock company of VHM where such heavy castings are commonly produced for the market. The supplied piece of the steel casting was cut into the smaller pieces for the better examination. The examination resulted in information about the casting macrostructure and chemical heterogeneity of chosen elements in the casting wall. The heterogeneity of the chosen elements (C, Mn, Si, Cr, S, P) is clearly shown in the worked out visual concentration maps. Based on the experimental data the measured results of segregations were confronted with the results of segregation modelling with the use of the commercial simulation software ProCAST. It resulted in the conclusion that the prediction of segregations is not in accordance with the reality. Furthermore, the results from the experimental casting are shortly compared with previously manufactured castings of the same type and the results summarizing the found range of macrosegregations of the tested sample are interpreted in the work conclusion.
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Importance of Upsetting Test for Numerical Simulation of Forming Processes
Tinka, Petr ; Dohnal, Ivo (referee) ; Řiháček, Jan (advisor)
The thesis deals primarily with the creation of a material model for numerical simulation using an upsetting test for steel 17 240, a layer of Delta 144 was applied on the steel. From the obtained values of force and path, a material model was created which serves for characterization material for numerical simulation. The simulation was performed in ANSYS Workbench 19.0. From this, force and path are obtained, which is used to compare with the upsetting test. It is clear from the comparison that the values do not differ too much, and it is possible to use this material for numerical simulation.
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Assessment of impact of arrangement of collagen fibres in arterial wall on its response in tension tests
Kratochvíl, Filip ; Chamrad, Jakub (referee) ; Burša, Jiří (advisor)
This thesis deals with organisation of collagen fibres in human blood vessel walls and with simulation models, which are used to calculate vessel behaviour. Firstly, the thesis focuses on the anatomy of human blood vessel system, mainly on the vessel structure and properties of some vessel components. Next, two models are presented, which can be used for the vessel wall in calculations, specifically models with straight and wavy collagen fibres. Moreover, some methods are described, which can be used to gain information about a vessel. Subsequently, relationships are derived needed for simulation of tension tests of these models, mainly to express the length of collagen fibres. In the practical part simulations of vessel behaviour during uniaxial tension test are carried out and histograms of local direction angles of collagen fibres in the unloaded state are created. In the end, results gained by simulations are compared with real available data.
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Application of an anemometric hot-wire probe to the measurement of a velocity field downstream of an automotive ventilation outlet
Šíp, Jan ; Tuhovčák, Ján (referee) ; Lízal, František (advisor)
This diploma thesis deals with the research of the flow in front of the benchmark automotive vent. Using thermoanemometry, the velocity field in the area in front of the vent was measured in detail and the intensity of the turbulence was calculated. Computational fluid dynamics of the air flow from the vent was also performed using the STAR-CCM + program. In addition, the influence of the surrounding surfaces simulating the real environment of the automobile on the air flow from the vent was investigated. The diploma thesis contains the calculation of measurement uncertainty. The purpose of this thesis is to obtain complex data on the velocity field and to use them for validation of Computational fluid dynamics.
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Pre-compliance Electromagnetic Immunity Tests
Růžek, Václav ; Polívka, Milan (referee) ; Soldán, Josef (referee) ; Dřínovský, Jiří (advisor)
The doctoral thesis deals with aspects of pre-certification tests of electromagnetic immunity in the automotive industry. The thesis analyses commonly used test methodology and mentions that standardized electromagnetic immunity tests performed by certified testing centres, which are extremely expensive and represents a considerable time load in the development of the vehicle. The thesis therefore proposes innovative ways for replacement of certification tests with an acceptable level of uncertainty. Key methods are seen in numerical simulations and modified test procedures when the vehicle is exposed by electromagnetic field. The proposed methods are deeply explored and their benefits are discussed and support by number of experiments. The results obtained with the pre-certification methods are objectively compared with the results of the certification measurements by FSV method. The work brings a proposal for a comprehensive test methodology including a discussion of risks and uncertainties with related issues.
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Strength design of the aircraft spur
Profota, Martin ; Vosynek, Petr (referee) ; Vrbka, Jan (advisor)
This master thesis deals with computational stress-strain analysis of the tailskid of airplane L410 NG with main focus firstly the check current design of the tailskid and then the design another design solution with the able to absorb as much as possible the deformation energy. Solution of this problem is performed using computational modeling utilizing numerical simulation of quasi-static and crash deformation load of the tailskid with using explicit Finite Element Method (FEM) in program ABAQUS v6.14. After the introduction with problem situation and tailskid assembly introductory part is devoted to the research study of various designs of the tailskid for different types of airplanes. There follows these theoretical general principles of thin-walled structures and buckling of them. Before the creating of the computational model itself, the explicit form of the Finite Element Method is better described. The conclusion of this thesis deals with the mutual comparison of the most advantageous design variants of the tailskid and the selection of the most suitable one of them for the airplane L410 NG.
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Numerical analysis of selected silicate based composites shrinkage
Drbušková, Magdaléna ; Vlk, Zbyněk (referee) ; Keršner, Zbyněk (advisor)
The thesis is divided into two main parts. In the first theoretical part is described the problems of shrinking including a comparison of Czech standard and Model Code 2010, Vol. 1. The second practical part of the master`s thesis is focused on the numerical analysis shrinkage primarily on the initial stage of this process. The experimentally obtained data are set approximations of the relative deformation using ShrCeC. Subsequently the numerical simulation of shrinkage of selected silicate specimens using a computer applications SpatiDist and FyDiK 2D. The real test specimens are modelled as two-component composite consisting of cement paste and aggregates. The result is a parametric study takes into account the influence of type and size of grain aggregate.
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Optimization of aluminium casting process using numerical simulation
Kolařík, Martin ; Lána, Ivo (referee) ; Krutiš, Vladimír (advisor)
The master’s thesis deals with the analysis of casting technology of the selected aluminium casting. It is a casting of a part of CNC milling machine and it is cast by gravity casting into a permanent mold. The defects which are the cause of a high percentage of nonconforming production were analyzed. Furthermore, the master’s thesis includes a complete analysis of filling and solidification of this casting in the ProCast simulation program. Numerical simulation results are verified and improved. Then the causes of problematic casting defects are proven on several calculated variants. Measures are proposed to minimize the tendency to produce castings with defects leading to nonconforming production.
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