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Fatigue characteristics of Metal Matrix Composites (MMC)
Judas, Jakub ; Věchet, Stanislav (referee) ; Zapletal, Josef (advisor)
This bachelor thesis is focused on analysis of fatigue characteristics of hybrid composite based on magnesium matrix QE22 reinforced with Al2O3 fibres and SiC particles. Test specimens of the composite material prepared by infiltration method were subjected to quasi-static tensile and compression test and discovered data were afterwards compared with the magnesium matrix. Cyclic response and low-cycle fatigue life were studied on the material under stress-control mode. All of the experiments were conducted at room temperature. Cyclic curves were fit with regression analysis in order to measure fatigue parameters of the hybrid composite. Cyclic and fatigue parameters were discussed and compared to similar magnesium alloy AZ91 reinforced with SiC particles.
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Low Cycle and High Cycle Fatigue Properties of Austempered Ductile Iron
Zapletal, Josef ; Bokůvka, Otakar (referee) ; Kunz, Ludvík (referee) ; Věchet, Stanislav (advisor)
The thesis is focused on assessment of fatigue behaviour of austempered ductile iron with nodular graphite. Optimal period of transformation was determined based on the best combination of stress and strain characteristics established by tensile test. Cyclic response and low-cycle fatigue life were studied under both stress-control and longitudinal strain-control mode at room temperature. For both modes, shapes of cyclic hardening curves are dependent on stress amplitude. Cyclic deformation curves (CDC) were fitted by power regression function. Results were compared with CDC established by multiple step test in both modes with verification of the influence of cyclic creep (high stress levels, stress-control mode). Experimental data of S-N curves are in agreement with the Manson-Coffin and the Basquin law. Fatigue and cyclic parameters were compared. Fatigue life time in high-cycle fatigue region was determined. Experimental data were fitted by suitable regression functions. Regression parameters and fatigue limit were established by means of each regression function. Experimental data in low- and high-cycle fatigue regions were used to construct S-N curve and to determine relevant parameters. Discontinuity of experimental data was not observed. Low-cycle fatigue behaviour was predicted. Approximation of tolerance bands was realized in high-cycle and both high and low cycle fatigue regions.
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Application of Technique of Oriented Foils in TEM
Buček, Petr ; Kruml, Tomáš (referee) ; Petrenec, Martin (advisor)
The master’s thesis is focused on the application of the technique of oriented foils in transmission electron microscopy. Dislocation structures were identified by this technique in both phases of polycrystalline austenitic-ferritic stainless steel SAF 2507 formed during low cycle fatigue at two plastic strain amplitudes ap. In individual grains the stress axis and the Schmid factors of active slip systems were determined. In austenitic grains, the planar structures were determined at both ap. In ferritic grains, the dislocation arrangement was different for the two observed ap. Individual screw dislocations and pile-up´s of edge dislocations were found at low ap = 1x10-4. Mixture of vein and wall dislocation structures were formed at high ap = 2x10-3. Observed dislocation structures were discussed in relation with the cyclic plastic response of the duplex stainless steel.
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Study of the Chaboche´s plasticity model complexity influence on the stress and deformation at the high pressure vessel
Paraska, Boris ; Obdržálek, Vít (referee) ; Vrbka, Jan (advisor)
The main aim of this thesis is to define material parameters of Chaboche model of plasticity. Adjustment of the parameters has to correspond to the experimental datas. These datas are represented by an uniaxial strain controlled test curve for fewer than two cycles and also by cyclic stress-strain curve. After that, an cyclic tension-compresion test for various parameters of Chaboche´s model of plasticity is simulated in an ANSYS software. Finally, the most suitable configuration of Chaboche´s model of plasticity is used for cylindrical thick-walled body. Cylindrical body represents a simplified model of high-pressure tank of fuel (diesel) – rail in Common Rail system.
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Low cycle fatigue of EN-AW 7075 aluminium alloy
Bártková, Denisa ; Liškutín, Petr (referee) ; Věchet, Stanislav (advisor)
The main goal of this bachelor thesis is analysis of low-cycle fatigue of wrought alluminium alloy EN-AW 7075. In theoretical part of thesis, current facts about alluminium alloys and fatigue behaviour of material are summarized. Practical part contains evaluation of tension tests and analysis of experiments in low-cycle fatigue region. In additional, the microstructure of an alloy was observed.
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Kinds of materials damage - II
Mašková, Lenka ; Nekvasil, Richard (referee) ; Neterda, Zdeněk (advisor)
Materials of production unit facilities are subjected to permanent damages while they are operating. Furthermore, there is a tendency to advance their working parameters that significantly increases risks of their damages. The goal of this thesis is to describe a process and mechanism of commonly occurred kinds of materials damage in the process industry. The thesis is focused on the material damage caused by the low-cycle fatigue and hydrogen embrittlement, and also the material disturbance evoked by the sudden fracture. Furthermore, the assessment technique of selected kinds of materials damage using theoretical formulae and their graphical representations using diagrams, schemes and figures for specific machineries are presented.
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Shape optimization of new circumferential steam turbine blade attachment type
Mívalt, Tomáš ; Petruška, Jindřich (referee) ; Polzer, Stanislav (advisor)
This thesis describes selection and shows calibration of material model, capable of describing cyclic softening of material. Stress-strain FEM analysis of circumferential blade attachment for last section of rotor blades of steam turbine is performed, expected lifetime of existing attachment is evaluated. Multi-parameter optimization of new-shape attachment was done, resulting in dimensions for new-shape attachment with longer lifetime. Improvements in strain amount in comparison with existing attachment were evaluated and possible RPM increase of turbine with new attachment type was calculated.
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Proposal of a new type of steam turbine blade attachement
Vrbický, Jiří ; Petruška, Jindřich (referee) ; Polzer, Stanislav (advisor)
This thesis describes design of new circumferential blade attachment on last grade of steam turbine and following stress-strain analysis by FEM with static and cyclic loading. It was created two new design of geometry, which were created based on existing and operating constructional solution of oblique double T blade attachment. It was made stress-strain FEM analysis on original design of blades. Its results served to realize change of construction. Their target was increase load capacity and service life of new types of blade attachment.
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Fatigue Behaviour of AZ31 and AZ61 Magnesium Alloys
Gejdoš, Pavel ; Lukáč, Pavel (referee) ; Kohout, Jan (referee) ; Podrábský, Tomáš (advisor)
This doctoral thesis deals with the fatigue behaviour of AZ31 and AZ61 magnesium alloy casted by advanced methods of casting squeeze casting. Based on the regression functions and measured fatigue data were determined fatigue characteristics of these alloys. The work also extends into the area of fatigue cracks in the AZ31 alloy. Were measured fatigue crack propagation rate on modified cylindrical specimens. The paper also outlines the possibilities for describing the fatigue behaviour of AZ61 alloy in extremely low-cycle fatigue.
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