National Repository of Grey Literature 277 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Description of fatigue behavior of additively manufactured polymer metamaterial structure
Helešicová, Petra ; Ševeček, Oldřich (referee) ; Trávníček, Lukáš (advisor)
Metamateriály jsou v posledních letech velmi často zkoumanou oblastí, jelikož umožňují přizpůsobení mechanických vlastností vyráběných součástí, které není možné získat s využitím konvenčních materiálů. Aby bylo možné metamateriály bezpečně využívat v provozu, je nutné popsat jejich chování při zatěžování. Prezentovaná diplomová práce je zaměřena na popis únavového chování 3D tištěné polymerní metamateriálové struktury. Práce je rozdělena na teoretickou a praktickou část. V teoretické části je provedena rešerše metamateriálů a jejich rozdělení, poté rešerše metod 3D tisku vhodných pro polymerní materiály a nakonec jsou představeny základy mechanického chování polymerů. V praktické části jsou postupně prováděny kroky pro určení odhadu únavové životnosti uvažované metamateriálové struktury pomocí čtyř kritérií. Pomocí experimentálních testů jsou naměřeny mechanické vlastnosti uvažovaného materiálu, které jsou vloženy do vytvořeného numerického modelu. Okrajové podmínky a zatížení modelu jsou zvoleny tak, aby odpovídaly reálným podmínkám při zatěžování. Numerický model je využitý pro určení kritických lokací ve struktuře a pro predikci únavové životnosti. Ve dvou kritických místech jsou zaznamenávány hodnoty napětí a přetvoření představující jednotlivé fáze cyklického zatěžování. Tyto hodnoty jsou použity pro predikci únavové životnosti.
Residual life assessment of hydrogen adsorption vessel subjected to cyclic loading
Brančan, Peter ; Vincour, Dušan (referee) ; Létal, Tomáš (advisor)
There was a need to asses the residual life of a cyclically pressurized adsorber of PSA unit used for the separation of hydrogen gas from a feedstock mixture, of which designed lifetime according to outdated standart ČSN 69 0010-4.20 was exceeded. The maximum design life was determined according to more recent design codes by the methodology of fatigue curves and comparison of results of outdated standard and 3 newer standards: EN 13445-3 - clause 17 and clause 18, and ASME BPVC Section VIII Div.2 - Level 2 was made. Due to the exceeding of the design life results by all of the standards the alternative approach of Fitness for service method based on linear elastic fracture mechanics of crack growth with the assumption of the occurrence of non-detectable defect size was used. The crack growth parameters were adjusted according to the study of crack propagation in hydrogen environment and implemented into the calculation of API-579-1/ASME FFS-1 Fitness for Service standard. The results showed, that pressure vessel can be further operated if regular NDT inspections are made. Inspection intervals of critical positions were determined from these results with compliance to safety and, at the same time, the scope of inspections has been modified to reduce expenses of carrying them out.
Thermomechanical fatigue of nickel-based superalloys
Pech, Filip ; Škorík, Viktor (referee) ; Šulák, Ivo (advisor)
The main objective of present bachelor thesis is to compile literature review of thermomechanical fatigue of nickel-based superalloys. Superalloys were developed to work at high temperatures, where sufficiently high strength, oxidation resistance, creep resistance, and resistance to other high temperature adverse effects have to be ensured. Superalloys are despite efforts to find alternatives still widely used and therefore it is necessary to know their properties and limitations. The present review compiles basic overview of nickel-based superalloys based on specialized publications. First of all, classification of Ni-based superalloys, chemical composition, along with an overview of the most important phases, which are affecting properties of superalloys were studied in detail. The second chapter describes basics of isothermal fatigue of materials, its definition, description of mechanism and basic fatigue life curves. Penultimate chapter of this literature review deals with thermomechanical fatigue and the structure of text is similar to chapter about isothermal fatigue. In the last chapter is given an overview of thermomechanical fatigue of different types of nickel-based superalloys.
Fatigue properties of materials prepared by SLM method
Hanáček, Josef ; Pantělejev, Libor (referee) ; Štěpánek, Roman (advisor)
This work deals with description of SLM (Selective Laser Melting) method, which is one of ALM (Additive Layer Manufacturing) method. In first part the general laws of fatigue and SLM method are described. The second part deals with the influence of processing parameters to final properties of material. The main goal of work is to determine dependence between processing parameters and mechanical properties of SLM processed components. Special attention is dedicated to fatigue properties.
Mechanical properties Al-alloy EN AW 7020 at increase temperatures
Slouka, Marek ; Kohout, Jan (referee) ; Věchet, Stanislav (advisor)
The master’s thesis deals with high strength aluminium alloys AlZn4Mg (EN AW 7020). This alloy is used for high strength, low density, a good corrosion resistant and a good weldability in protective atmospheres. At first this thesis is described to aluminium alloys, ways of manufacturing and history. Next this thesis mainly deals with wrought aluminium alloys, heat treatment this alloys and alloys Al-Zn-Mg. Tensile tests were made of alloys EN AW 7020 at room temperature and increased temperature. Next this alloy was made of fatigue test and metallographic analysis. The model was construct. This model describe to behaviour alloy at increased temperature and this model was compared with measure values. This thesis describe to behaviour of study alloy at room temperature and increased temperature.
Fatigue evaluation using electromyography
Mošnerová, Jitka ; Chmelař, Milan (referee) ; Janoušek, Oto (advisor)
The aim of the diploma thesis is the design and implementation of methods for detecting fatigue in electromyogram (EMG). At first is done a literature review on the topic of fatigue detection in electromyography (EMG). Measurement of fatigue-induced changes in the EMG signal is performed on ten subjects using the Biopac ©. Next is in the thesis solved the selection of the optimal methods of evaluating the fatigue-induced changes in EMG recording using statistical testing. In the final part of the thesis is discussion on the results of statistical testing, creation a user interface in Matlab © and comprehensive instructions for laboratory focused on the topic of fatigue in the EMG signal.
Kinetics of Short - crack Growth in Superduplex Steel
Bártová, Lenka ; Pantělejev, Libor (referee) ; Polák, Jaroslav (advisor)
The fatigue life and the kinetics of short crack growth in specimen of austenitic-ferritic duplex steel cycled with constant stress amplitude and different mean stresses is studied. Fatigue life was determined on smooth cylindrical specimens. Strain amplitude and mean strain were recorded. Short crack growth was studied in cylindrical specimens with a shallow notch. Cyclic straining was interrupted and crack length was measured using an optical microscope mounted on the testing machine. Crack length and crack growth rates were evaluated. The effect of the mean stress on the rate of short cracks and fatigue life were discussed.
Assesment of assembling inaccuracy on the coil spring lifetime
Stavárek, Václav ; Hadaš, Zdeněk (referee) ; Lošák, Petr (advisor)
This bachelors thesis is focused on helical compression springs with rectangular wire cross-section. In cooperation with an unnamed company it examines few possible causes of their failure rate. This thesis also includes experimental measurement of change of the spring stiffness after it underwent a high number of cycles.
Design of concrete structures with FRP reinforcement
Januš, Ondřej ; Girgle, František (referee) ; Štěpánek, Petr (advisor)
The diploma thesis presents design of construction with FRP reinforcement. Including design process of cross-section with FRP reinforcement exposed to bending moment and shear force at ultimate limite state according to given standards and guidelines. Long term physical and mechanical properties of FRPs are taking into account. There are also compared load capacities of cross-section exposed to combination of bending moment and axial force, which were designed according to mentioned standards. In another part of diploma thesis there is a design of construction (precast gatehouse) with FRP reinforcement and steel reinforcement with ordinary and lightweight concerete.

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