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Computational Simulation of Mechanical Tests of Isolated Animal Cells
Bansod, Yogesh Deepak ; Kučera,, Ondřej (referee) ; Florian, Zdeněk (referee) ; Canadas, Patrick (referee) ; Burša, Jiří (advisor)
Buňka tvoří složitý biologický systém vystavený mnoha mimobuněčným mechanickým podnětům. Hlubší pochopení jejího mechanického chování je důležité pro charakterizaci její odezvy v podmínkách zdraví i nemoci. Výpočtové modelování může rozšířit pochopení mechaniky buňky, která může přispívat k vytvoření vztahů mezi strukturou a funkcí různých typů buněk v různých stavech. Za tímto účelem byly pomocí metody konečných prvků (MKP) vytvořeny dva bendotensegritní modely buňky v různých stavech: model vznášející se buňky pro analýzu její globální mechanické odezvy, jako je protažení nebo stlačení, a model buňky přilnuté k podložce, který vysvětluje odezvu buňky na lokální mechanické zatížení, jako třeba vtlačování hrotu při mikroskopii atomárních sil (AFM). Oba zachovávají základní principy tensegritních struktur jako je jejich předpětí a vzájemné ovlivnění mezi komponentami, ale prvky se mohou nezávisle pohybovat. Zahrnutí nedávno navržené bendotensegritní koncepce umožňuje těmto modelům brát v úvahu jak tahové, tak i ohybové namáhání mikrotubulů (MTs) a také zahrnout vlnitost intermediálních filament (IFs). Modely předpokládají, že jednotlivé složky cytoskeletu mohou měnit svůj tvar a uspořádání, aniž by při jejich odstranění došlo ke kolapsu celé buněčné struktury, a tak umožňují hodnotit mechanický příspěvek jednotlivých složek cytoskeletu k mechanice buňky. Model vznášející se buňky napodobuje realisticky odezvu síla-deformace během protahování a stlačování buňky a obě odezvy ilustrují nelineární nárůst tuhosti s růstem mechanického zatížení. Výsledky simulací ukazují, že aktinová filamenta i mikrotubuly hrají klíčovou úlohu při určování tahové odezvy buňky, zatímco k její tlakové odezvě přispívají podstatně jen aktinová filamenta. Model buňky přilnuté k podložce dává odezvu síla-hloubka vtlačení ve dvou různých místech odpovídající nelineární odezvě zjištěné experimentálně při AFM. Výsledky simulací ukazují, že pro chování buňky je rozhodující místo vtlačení a její tuhost určují aktinová povrchová vrstva, mikrotubuly a cytoplazma. Navržené modely umožňují cenný vhled do vzájemných souvislostí mechanických vlastností buněk, do mechanické úlohy komponent cytoskeletu jak individuálně, tak i ve vzájemné synergii a do deformace jádra buňky za různých podmínek mechanického zatížení. Tudíž tato práce přispívá k lepšímu pochopení mechaniky cytoskeletu zodpovědné za chování buňky, což naopak může napomáhat ve zkoumání různých patologických podmínek jako je rakovina a cévní choroby.
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Properties of polyethylene blown-films dependent on their composition
Štaffová, Martina ; Poláček, Petr (referee) ; Tocháček, Jiří (advisor)
This work deals with the influence of quantity of recycled material on physical properties of blown-film. The task of this work is to prepare set of laboratory made films with amount of LLDPE granulate from 0 to 100 % with addition of LDPE recycled material and furthermore with addition of filler, calcite. The following methods were used for characterization of blown films: tensile test, differential scanning calorimetry, Fourier transform infrared spectroscopy, confocal laser scanning microscopy. The same measurements were performed also on industrial made blown-film.
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3D FDM printer reprap and parameters of print
Kratochvíl, Tomáš ; Dvořák, Jaromír (referee) ; Zemčík, Oskar (advisor)
This master thesis summarizes the current knowledge about non-commercial 3D printing FDM technology. The goal of this thesis is to demonstrate the gained knowledge by building a 3D printer which can partially replicate itself, and to evaluate its technological parameters. The experimental part of this work is focused on the impact of the changes in technological parameters of printing on mechanical properties of printed parts.
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Parameter Identification for Elastic-plastic Material Models from Experimental Data
Jeník, Ivan ; Šebek, František (referee) ; Kubík, Petr (advisor)
This master's thesis deals with the identification of the material flow curve from record of tensile test of smooth cylindrical specimen. First, necessary theory background is presented. Basic terms of incremental theory of plasticity, tensile test procedure and processing its outputs are described. Furthermore, possibilities of mathematical expression of the elastic-plastic material constitutive law, thus mathematical expression of the material flow curve itself. Mechanism of ductile damage of material is explained briefly as well. Overview of recent methods of the flow curve identification is given, focused on cases, when the stress distribution in a specimen is not uniaxial. That is either kind of analytic correction of basic formulas derived for uniaxial stress state, or application of mathematical optimization techniques combined with numerical simulation of the tensile test. Also unusual method of neural network is mentioned. For 8 given materials, the flow curve identification was performed using different methods. Namely by analytic correction, optimization, sequential identification and neural network. Algorithms of the last two methods were modified. Based on assessment of obtained results, application field and adjusting the parameters of single algorithms was recommended. It showed up, that an effective way to the accurate and credible results is the combination of different methods during flow curve identification procedure.
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Small-punch test of structural steels at low temperatures
Němčíková, Eva ; Hůlka, Jiří (referee) ; Hadraba, Hynek (advisor)
Diploma thesis is focused on comparison of small punch test results and tensile test results. For experiments were chosen steel P91, 10Ch2MFA, 20CrNi2MoV, 11 416 and 42 2707. These steel are used in nuclear power engineering, or they were developed for this purpose. Basic mechanical characteristics, namely ultimate tensile stress and yield stress, were evaluated from small punch test records of observed materials. This is done via convenient correlation relationships. Obtained values were compared with values obtained by conventional tensile tests. There are mentioned own suggested correlation relationships and comparison of temperature curves gained from small punch test and tensile test in the thesis. Assessment of microstructure of observed materials and analysis of fracture surfaces was provided as well. It was found out, that for assessing basic mechanical characteristics (ultimate tensile stress and yield stress) is the best to suggest own correlation relationships, instead of using universal relationships from literature. The fracture mechanism of all types of assessed steel was ductile in entire temperature range (up to -40 °C).
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Hardenning of polymeric composites by nanotubes
Kuběna, Martin ; Zajíčková, Lenka (referee) ; Pantělejev, Libor (advisor)
This diploma thesis focuses on the influence of carbon nanotubes (CNTs) on the mechanical properties of a composite material with polyurethane (PU) matrix. The material was supplied in the form of thin films with thickness from 0.2 mm to 1.2 mm. The theoretical part of this thesis describes the production technology, properties and applications of composite materials PU/CNTs, and also deals with preparation technology and properties of both components of this composite material separately. The theoretical part also describes the principle of tensile testing of polymer materials. The experimental part of the thesis was primarily focused on comparing the tensile properties of a composite material PU/CNTs with tensile properties of pure PU. At first, tensile properties of pure PU were investigated, while the influence of various factors like strain rate, specimen thickness, heat treatment and aging was examined. In adition, stress relaxation tests and tests with strain rate jumps were performed on pure PU specimens. Then composite PU/CNTs was tested in tension and the results were compared with the results of tensile tests of pure PU. Composite material PU/CNTs was prepared with various concentrations, so it was possible to determine the effect of CNTs content on the tensile properties of the composite. The last part of this thesis deals with tensile tests of PU composite material with functionalized carbon nanotubes (PU/FCNTs), where the influence of surface modification (functionalization) of CNTs on the tensile properties composites was investigated. It was shown that the effect of both CNT and FCNT on mechanical properties of the composite is not significant. This conclusion was discussed on basis of the works of other authors, which do not unambiguously proved the positive effect of CNT or FCNT on mechanical properties of composites with polymer matrix.
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Solution of bendig technology problems of thinn walled profiles
Matoušek, Karel ; Forejt, Milan (referee) ; Samek, Radko (advisor)
Reconnaissance of problems and parameters of square hollow profile bend. Finding (identification) of deformation of cross-section. Finding of suitability of unannealed material for component part. Finding of mechanical characteristics of welds and influence of their bend position. This finding was done on the basis of comparison of tensile tests and consequently aplicated to specific part where the suitability for use of unannealed material were proved.
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Computational modelling of mechanical tests of isolated cells
Sůkal, Petr ; Fuis, Vladimír (referee) ; Burša, Jiří (advisor)
The master’s thesis deals with computational modelling of mechanical testing of isolated cells, particularly of single-axle tensile test. The aim is to imitate the real deformed shape known from experiments. At first, the structure of each cell component is described and analyzed according to their significance for mechanical behavior. The outline of basic mechanical tests used for cell testing is discussed next. A structural computational model comprising all components significant for mechanical purposes is created for the modelling. Those components are nucleus, cytoplasm, cell membrane and cytoskeleton. Due to the problems with convergence the model was divided into two parts. The first one treats separately the shape of cytoskeleton and the second one treats the shape of communicating components (nucleus, cytoplasm and cell membrane). Both of those partial models succeed in reaching the deformations according to the experiments.
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Influnce of chemical composition on mechanical properties of LLDPE stretch film
Vojáček, Jakub ; Tocháček, Jiří (referee) ; Poláček, Petr (advisor)
Thesis summarizes the problems of production and use of stretch film. The change of strength, ductility and relative relaxation effect in different times of drawing from role in three weeks was observed. Further, change of strength and ductility due to changes in the rate of deformation, exposure to accelerated aging in a UV chamber and changes in the loading direction were observed. Mechanical tests were realized on a tensile tester, relaxation tests on DMA and crystallinity changes were observed on the DSC. Relationship between chemical composition of stretch film and mechanical and thermomechanical properties were studied. It was found that chemical composition essential for stretch film properties. However, due to the impossibility to distinguish effects of chemical composition and process parameters was impossible to find clear relation describing this relationship.
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Physical ageing of polypropylene
Weiss, Jiří ; Kučera, Jaroslav (referee) ; Tocháček, Jiří (advisor)
Physical aging of commercially produced polypropylene homopolymers Mosten was studied. The work is focused on monitoring the changes in physical properties of polymer in the time period 90 days from the date of preparation of the test specimen. The aging of polymers was realized at storage temperatures of 23 and 80 °C. The changes in crystallinity, yield strength, modulus, elongation and impact strength using DSC method, tensile tests and impact tests according to Charpy were monitored. Molecular weight distribution was determined by means of GPC at each polymer. Relationships between the changes in physical properties and polymer molecular weight were sought.
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