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On the stress distribution near the tip of a sharp notch
Ostratický, Jakub ; Hrstka, Miroslav (referee) ; Profant, Tomáš (advisor)
The notch is a stress concentrator from the point of view of elasticity theory and the knowledge of the description of this stress in the vicinity of its tip is necessary for the correct functionality of a wide range of mechanical components and products. The stress at the tip of the notch is singular and it is technically impossible to prevent the initiation of cracks in its vicinity. However, it is known from fracture mechanics that the initiation and propagation of cracks is not influenced by the magnitude of the stress at their tips, but its intensity characterized by the so-called stress intensity factor. In the case of a notch, it is a generalized stress intensity factor or simply the amplitudes of the singular parts of the stress filed. These coefficients cannot be determined directly from the results of widely used numerical methods such as FEM, but it is necessary to use linear fracture mechanics methods based on the asymptotic solution of the equilibrium equations in elasticity. The presented work deals with the case of a symmetric sharp notch in an isotropic material under the mode I or II loadings. The stress singularity and the related stress intensity factor at the notch tip are analysed and evaluated. The derived asymptotic solution is compared with the results obtained from the FEM analysis.
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Smart Structures with Integrated Piezoelectric Materials
Pinček, Ladislav ; Hrstka, Miroslav (referee) ; Hadaš, Zdeněk (advisor)
Táto práca sa venuje skúmaniu smart materiálových vlastností auxetickej štruktúry s elektromechanickou premenou vyvinutej na VUT. Práca sa postupne v jednotlivých bodoch zaoberá zostavovaním laboratórnych vzoriek smart materiálového systému, experimentálnym vyšetrovaním elektromechanických parametrov, dizajnom modelu a návrhom technických aplikácii. Pre danú štruktúru bolo navrhnutých viacero technických využití. Navrhované technické využitia boli experimentálne alebo simulačne skúmané a bol vyhodnotený potenciál pre ďalší výskum.
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Mechanical analysis of roof lift
Sárkány, Zoltán ; Hrstka, Miroslav (referee) ; Fuis, Vladimír (advisor)
The bachelor's thesis deals with the mechanical analysis of a roof lift in 2D, which consists of nine solid bodies. The first part of the work covers the basic necessary theoretical knowledge to solve the problem in terms of statics and dynamics. The second part of the work is the solution itself, where the equations of static equilibrium are compiled for different states of motion. Movement states where the elevator does not move at a constant speed are solved in terms of dynamics. The solution considers the effects of passive resistances. The output of the work is the resulting forces in the bonds and the assessment of the functionality of the bonds. The numerical solution was performed using the MATLAB program.
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Simulation of the Laval rotor supported by nonlinear bearings
Krček, Aleš ; Hrstka, Miroslav (referee) ; Lošák, Petr (advisor)
The presented diploma thesis deals with simulation of Laval rotor supported by nonlinear bearings. The first part of thesis deals with research, which is focused on description of Laval rotor and motion equations for case of rigid and flexible rotor, also on description and modeling of hydrodynamic and magnetic bearing, which is considered in thesis. The second part of thesis deals with simulation of rotor for different approaches to modeling hydrodynamic and magnetic bearings. Using simulations performer in time domain, the dynamic behavior of Laval rotor is evaluated and compared. Simulations are performer in MATLAB.
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Influence of early and late drought on grain proteins content and composition in early and late variety of wheat
Vojteková, Vanesa ; Zemanová, Jana (referee) ; Hrstka, Miroslav (advisor)
In this bachelor thesis, the influence of early and late drought on grain protein content and composition in an early and late variety of winter wheat was studied. The varieties used were Avenue and Tobacco.One part of the plants was cultured under the conditions of early drought (bloom season), another part was grown under the conditions of late drought (grain filling season), the last part was grown under the conditions of natural irrigation. Half of the plants were fertilized using nitrogen fertilizer (200 kg N/ha), the second half of plants were without nitrogen fertilizer (0 kg N/ha). Wet gluten, crude protein content, gliadin and glutenin content were determined from flour samples. Results were evaluated by analysis of variance. Drought resistance depends on the genotype. Tobak genotype is more tolerant to climatic conditions, but the drought had a more significant effect on gliadin and glutenin ratio than on the Avenue genotype. Late drought increased wet gluten content in both genotypes and both types of fertilization. On the other hand, the early drought did not affect wet gluten content. Early drought decreased gliadin content, with the exception of Avenue genotype without fertilization. Early drought also increased glutenin content. Late drought increased glutenin content only in the unfertilized variant. Early drought increased glutenin content which leads to decreased gliadin content, especially for nitrogen fertilization. Late drought caused a decrease of gliadin and glutenin ratio, except for Tobak genotype with fertilization. Late drought increased crude protein content, except for Tobak genotype without fertilization. Early drought decreased crude protein content, especially for the unfertilized variant.
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Influence of increased carbon dioxide concentration on grain protein composition in early and late wheat variety
Smrčková, Kamila ; Vítová, Eva (referee) ; Hrstka, Miroslav (advisor)
This bachelor thesis deals with the effect of increased CO2 concentration (700 ppm) on the content and composition of wheat grain proteins in early (Avenue) and late (Tobak) wheat varieties. Three methods were used to determine the proteins in wheat grain: the Kjeldahl determination of crude protein content, the determination of wet gluten, and finally the gravimetric determination of gliadins and glutenins after extraction. A different response of the varieties to the increased CO2 concentration was found. The early Avenue variety was much more sensitive to the effects of increased CO2 concentrations. The gliadin content decreased, while the glutenin content increased with increasing CO2 concentration. The total gluten protein content increased in elevated CO2 concentration, independently of nitrogen fertilization. Its content correlates in our work with the content of wet gluten.
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Numerical modeling of failure of a particle composite with ceramic matrix
Kosorín, Michal ; Hrstka, Miroslav (referee) ; Majer, Zdeněk (advisor)
Subcritical crack growth in composite materials plays quite an important role in determination of the service life and leads to the defects growth below the fracture toughness. The thesis presents search of the several scientific works dealing with the determination of the crack growth direction in composite materials. The aim of this diploma thesis was to create 2D and 3D finite element models to analyse crack growth in Low Temperature Co-fired Ceramics (LTCC). These models were compared based on the time calculation of the crack propagation under the subcritical growth conditions.
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ON THE ENERGY RELEASE RATE OF THE CRACK EMANATING FROM THE INCLUSION INTERPHASE
Profant, T. ; Hrstka, M. ; Klusák, Jan ; Kersner, Z.
The problem of the crack emanating from the interphase region of the circular inclusion is investigated. The problem combines an application of dislocation distribution technique for a crack modelling and the method of boundary integral equations to approximate the loading along the boundary of the domain containing an inclusion. The topological derivative method provides the combination of both approaches and results to the evaluation of the energy release rate of the arbitrary oriented microcrack emanating from the inclusion and matrix interphase. The fundamental solution intended to the boundary integral method such as the continuously distributed dislocation technique is based on the application of Muschelishvili complex potentials in the form of the Laurent series. The coefficients of the series are evaluated from the compatibility conditions along the interfaces of inclusion, interface and matrix.
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ON THE ENERGY RELEASE RATE OF THE CRACK EMANATING FROM THE INCLUSION INTERPHASE
Profant, T. ; Hrstka, M. ; Klusák, Jan ; Kersner, Z.
The problem of the crack emanating from the interphase region of the circular inclusion is investigated. The problem combines an application of dislocation distribution technique for a crack modelling and the method of boundary integral equations to approximate the loading along the boundary of the domain containing an inclusion. The topological derivative method provides the combination of both approaches and results to the evaluation of the energy release rate of the arbitrary oriented microcrack emanating from the inclusion and matrix interphase. The fundamental solution intended to the boundary integral method such as the continuously distributed dislocation technique is based on the application of Muschelishvili complex potentials in the form of the Laurent series. The coefficients of the series are evaluated from the compatibility conditions along the interfaces of inclusion, interface and matrix.
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Recovery of the method for assessment of fatty acids
Gross, Michal ; Hrstka, Miroslav (referee) ; Vítová, Eva (advisor)
The objective of this bachelor thesis is to verify recovery yield used for determination of fatty acids based on gas chromatography with flame-ionization detection. In the theoretical part, fatty acids and lipids are characterized and extraction of lipidic fraction from food samples with its subsequent adjustments is suggested. Furthermore, the principle and current instrumentation of capillary gas chromatography with flame-ionization detection and standard parameters for validation of the analytical method are specified. In the experimental part, verification of recovery yield of the method for assessment of fatty acids was performed. The used method includes extraction of lipids from a sample in accordance with the standard ISO 1735 regulation and transesterification of both free and bounded fatty acids catalysed by boron trifluoride according to the ISO 12966-2 standard regulation. The produced methyl esters can be effectively determined using gas chromatography with flame-ionization detector. Analysed samples of rapeseed oil and tilsiter-type cheese were purchased in a common food market.
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