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Elastoplastic analysis of stress and deformation and determination of fracture parameters of bodies with stress concentrators under tensile loading
Dubravec, Kristián ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The aim of this thesis is the construction of a diagram of fracture strain for high strength steel OCHN3MFA and its application for the estimation of fracture toughness of this material. The first part of the thesis contains the necessary theoretical framework for numerical modelling of tensile tests of various specimens - smooth specimen, specimen with a notch and specimen with a circumferential crack, it describes the influence of triaxiality on the fracture of bodies and the possibilities of construction of the diagram of fracture strain. Subsequently, a numerical model of these specimens is created using the finite element method (FEM). A non-linear, elastoplastic calculation is performed. Fracture is identified by means of comparing the true stress versus the strain obtained from tests with the finite element analysis results. Stress–strain states of specimens at the moment of fracture are obtained from a numerical model. A diagram of fracture strain is constructed, and it is used to estimate the fracture toughness of a cracked body. Finally, a local approach, which uses the diagram of fracture strain, and a classical approach of fracture mechanics, especially the stress intensity factor, are compared.
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The design of clamping equipment for tensile testing of car door hinges
Daněk, Jiří ; Čípek, Pavel (referee) ; Klapka, Milan (advisor)
This thesis deals with the problem of clamping fixture for tensile tests of car door hinges. The aim of the thesis was to design a new preparation that will replace the current one that is not satisfactory. All the goals of the thesis were met, the output of the thesis is a design of a product that meets the requirements of the standards and the customer. On the basis of the control calculations, drawing documentation was created and then Edscha had the new product manufactured. The product has been in operation for more than half a year and meets all requirements.
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Structural and Mechanical Characteristics of Nickel-Alloyed Ductile Cast Iron
Tesařová, Hana ; Kohout, Jan (referee) ; Kruml, Tomáš (referee) ; Konečná,, Radka (referee) ; Pacal, Bohumil (advisor)
The aim of this dissertation work is the evaluation of the influence of nickel alloying on the structure and mechanical properties, both monotonic and dynamic, of nodular cast iron with ferritic and bainitic matrix. Two chock melts with 0.5 and 2.7 % Ni were used to study the nickel influence. The quantitative evaluation of structure of these melts using image analysis was done and basic tensile mechanical properties were determined. Subsequently, the time optimization of two-stage ferritic annealing and isothermal austempered heat treatment at 375 °C was performed with the aim to obtain optimal ferritic and bainitic structures with best static and dynamic mechanical properties. After ferritic annealing the nickel alloying contributes to substitution hardening of ferritic matrix which positively affects its strength and other mechanical properties. The higher nickel content in the bainitic structure causes the shift of phase transformation times to longer times which results in restricted production of small carbides and in bigger volume of retained austenite. These features were confirmed by observation in transmission electron microscope. Precise tensile and low cycle fatigue tests at temperatures 23 and – 45 °C were performed on the optimized structures of both nodular cast irons. As a result of the notch effect of graphite nodules, microplastic deformation of both nodular cast irons was observed at stresses which were lower than the yield stress. The Hollomon's equation very well describes the individual parts of tensile curves for both nodular cast irons including their mutual comparison. From the low cycle fatigue tests, the cyclic hardening/softening curves, the evolution of elastic modulus and hysteresis loop shape parameters, cyclic stress-strain curves and fatigue life curves were obtained for both temperatures and materials. Moreover, the decrease of retained austenite volume was measured by neutron diffraction and the evolution of surface relief was characterized during cyclic straining for both austempered nodular cast irons at both temperatures. On the basis of these results both cyclic plasticity and fatigue degradation mechanisms in relation to the cyclic strain localization were described for both nodular cast irons.
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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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Determination of the mechanical properties of materials used for 3D printing
Černý, Martin ; Sliwková, Petra (referee) ; Sedlák, Josef (advisor)
The thesis deals with the determination of mechanical properties of materials used for 3D printing (ABS, nylon and PLA). Standardized samples produced using a 3D printer using the Fused Deposition Modeling method were subsequently used for mechanical testing. The work is also extended to determine the mechanical properties of samples made by Soft Tooling. For the production of Soft Tooling samples, polyurethane resins SG 2000 and SG 145 were used. Individual materials were analyzed by mechanical tests (tensile test and hardness test). Surface integrity parameters have also been determined for 3D-printed materials. Parameters were selected from the individual tests (tensile strength, modulus of elasticity) ductility and hardness), which were subsequently statistically processed. The work is concluded by evaluating the results obtained, which were compared with the values given in material sheets.
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Mechanical properties of glass fibers
Ševnina, Marija Vladimirovna ; Svěrák, Tomáš (referee) ; Čech, Vladimír (advisor)
The bachelor thesis deals with the examination of mechanical properties of unsized glass fibers and commercially sized glass fibers. The main objective is to determine the tensile strength, modulus of elasticity, and ductility for the fibers depending on the surface modification. To determine these properties, fiber diameters were measured using an Olympus BX 50 optical microscope followed by a tensile test on the Universal Testing Machine, ZWICK / Z010 / TH2A.
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Analysis of mechanical properties of polymers and polymer compsites from video record of tensile test
Ščudlová, Jolana ; Nezbedová, Eva (referee) ; Žídek, Jan (advisor)
This thesis described mechanical tests with monitoring of camera. The aim of this work is to obtain additional information about material behavior during the test. The mechanical tests were monitored high-definition (HD) digital video-camera and camera with high resolution. The method was applied to the tensile test and Pennsylvania notch test (PENT test). The videorecordings were processed with the assistance image analysis method. The marks were placed on both of these specimens, mutual movement these marks were used to obtain following characteristics. It was Poisson’s ratio and true stress by tensile test. By PENT test it was rate growth crack. The investigated material was elastomeric polyurethane filled by biodegradable polyhydroxybutyrate for tensile test. Second material was polypropylene for PENT test. The camera is adding to the test gives extended information about the material and better interpretation results.
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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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The influence of recycled material on weathering and accelerated aging of high density polyethylene
Borguľová, Eva ; Tocháček, Jiří (referee) ; Bálková, Radka (advisor)
The thesis deals with the testing of moulded high-density polyethylene (HDPE) samples that have been exposed to natural weather conditions for 9 months and accelerated ageing at 65 °C for 1000 hours. One sample was white in colour (made from commercial granulate) and four were black, one of which would have been prepared from 10 year old recycled material (recyclate), the other three were blends of this with white HDPE at 30, 60 and 90 % ratios. Infrared spectroscopy with ATR technique, static and dynamic tensile testing, differential compensation calorimetry and thermogravimetric analysis were used to characterize the changes in composition, structure and mechanical properties. The results showed that photooxidation occurred in all samples after the 1st month of exposure. Inhibition of degradation was noted after 3 months but increased again with time. The change in the mechanistic properties over time is a response of cleavage and recombination, but also of crystallization or crosslinking. The black color proved to be a stabiliser, as the clear samples remained largely tough after accelerated ageing, in contrast to the white sample which became quite brittle, as confirmed by the highest carbonyl index value. Thus, it can be assumed that with moderate UV stabilization the recyclable material is reusable for production, especially the proportion of 30 % (higher proportions caused a decrease in toughness).
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