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Differential equations in models of motion of dislocations
Vydrová, Jana ; Řehák, Pavel (referee) ; Šremr, Jiří (advisor)
This thesis deals with the differential equation which appears in the mathematical model by thermally activated motion of dislocations. It’s focused on screw dislocations in bodycentred cubic metals. Especially solves derivation of the pertinent differential equaiton and then explores properties of their solutions. To research these properties are used knowledges and techniques of qualitative theory of differential equations.
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Influence of Explosive Hardening on the Structure and Characteristic of Hadfield Steel in Terms of use in the Railway Transport
Havlíček, Petr ; Podrábský, Tomáš (referee) ; Nesvadba,, Petr (referee) ; Schmidtová,, Eva (referee) ; Stránský, Karel (advisor)
The high alloyed austenitic manganese steel, the Hadfield steel, thanks to its good wear resistance of the work surface and maintaining the high toughness of the internal material in the same time, is successfully applied for casted crossings. The crossings are the most dynamic stressed components in the railway turnouts. Thanks to low surface and sub-surface hardness the occurrence of plastic deformation and the progressive wear of the crossing running surfaces can be found since the initial stages of the crossing operational life. One possibility how to increase the surface and the sub-surface hardness and this way improve the dimensional stability and the crossing lifetime as well is to apply the explosive hardening of the crossing running surfaces. The technology mentioned above means the application of the explosives in the imminent nearness to the running surface of the crossing, when the high pressure wave acting within the extremely short period actuates the plastic deformation of the material structure. The work deals with analysis of influence of explosive hardening on the structure and characteristic of Hadfield steel. The explosive hardened samples have the surface and the sub-surface hardness checked and the microscopic analysis and X – ray diffraction is applied, including the TEM analysis as well carried out by the transmission electronic microscope. The characteristics experimental testing including outcomes from assessment of the contact – fatigue load of the explosive hardened Hadfield steel samples are the part of the work as well. As an experiment final part the outcomes of the long –term validation, the surface hardness and wear of the crossing running surfaces of the explosive hardened crossing already installed into the Czech Republic railway track are introduced as well.
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Problems of the complex potentials of the isotropic elasticity
Padělek, Petr ; Druckmüller, Miloslav (referee) ; Profant, Tomáš (advisor)
The presented Bachelor Thesis investigates the problem of the complex potentials in the isotropic elasticity. The objective of the work is acquiring the components of the stress tensor and the displacement vector which describe the elasticity of continum. This problem is primarily solved on the mathematical level by means of the Airy stress function and the Muschelishvili´s complex potentials. The thesis is supplemented with the necessary theory of the elasticity and finally the concrete solution of the edge dislocation in the infinite domain is demonstrated and compared with the results acquired by FEM method.
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Damage mechanisms in nickel-based superalloy René 41 subjected to fatigue
Babinský, Tomáš ; Pippan, Reinhard (referee) ; Růžička,, Milan (referee) ; Polák, Jaroslav (advisor)
Předkládaná práce se zabývá vznikem poškození ve tvářené niklové superslitině René 41, která je podrobena únavovému zatěžování za pokojové a zvýšené (800 °C) teploty. Slitina byla zkoumána ve dvou termodynamických stavech: po rozpouštěcím žíhání a po stárnutí. Jednoosé zkoušky nízkocyklové únavy byly prováděny symetricky vzhledem k řízené veličině, kterou byla celková podélná deformace. Za účelem studia mechanismů poškození a jejich souvislosti s plastickou deformací byly aplikovány techniky elektronové mikroskopie doplněné o analýzu cyklické odezvy ve formě hysterezních smyček statistickým přístupem. Navíc byly provedeny přerušované únavové zkoušky za účelem studia vývoje povrchového reliéfu ve vztahu k dislokační substruktuře, k čemuž bylo opět využito elektronové mikroskopie. Porušení za pokojové teploty bylo povětšinou transkrystalické, únavové trhliny iniciovaly především uvnitř zrn z povrchového reliéfu. Srovnáme-li dva zkoušené stavy, stárnutý materiál vykazoval vyšší hodnoty cyklického napětí a při srovnatelném napětí dosahoval vyšších životností. Cyklická deformace byla od prvního cyklu lokalizována do persistentních skluzových pásů. Bylo zjištěno, že většina skluzových pásů vzniká na začátku únavového života, kvůli čemuž jsou koherentní precipitáty ‘ významně deformovány pouze na začátku únavového života. Skluz v persistentních skluzových pásech vedl k vytvoření povrchového reliéfu ve formě skluzových schodů, extruzí a intruzí. Vznik povrchového reliéfu byl podrobně diskutován s existujícími modely. Vysokoteplotní expozice měla za následek oxidaci povrchu, zejména na oslabených hranicích zrn, kde iniciovaly a následně se šířily únavové trhliny. Výsledné poškození bylo tudíž interkrystalické.
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General overview of GaN devices and transport properties of AlGaN/GaN HEMT structures - impact of dislocation density and improved design
Hulicius, Eduard ; Hájek, František ; Hospodková, Alice ; Hubík, Pavel ; Gedeonová, Zuzana ; Hubáček, Tomáš ; Pangrác, Jiří ; Kuldová, Karla
GaN-based nanostructures are used for many present semiconductor devices. The main topics are structures for blue LEDs and LDs, but there are also other interesting and important GaN devices namely for power electronics, scintillators and detectors as well as High Electron Mobility Transistors (HEMT). Reduction of dislocation density considerably increases electron mobility in 2DEG. All presented results support our expectation that a suitably designed AlGaN back barrier can help to prevent this phenomenon.
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Case report of physiotherapy care of patient with dislocation of elbow
Bechyňák, Václav ; Nováková, Tereza (advisor) ; Vaňous, František (referee)
Title of bachelor's thesis: Case report of physiotherapy care of patient with dislocation of elbow Thesis aim: Aim of this bachelor's thesis is summary of theoretical knowledge and study of rehabilitation in context with traumatology, especially dislocation, of elbow joint. Then use this knowledge in practice with patient with status post dislocation of elbow joint. Method: Theoretical part of bachelor's thesis includes anatomic, kinesiological and biomechanical findings of elbow joint in relationship with other structures. In other section are described issues of traumatology of elbow joint, with focus on elbow dislocations. There is detailed description of examination a therapy, mainly meant by rehabilitation care with using physical therapy and physiotherapeutic methods. In special part of thesis I processed detailed case report of 55 years old female patient with status post posterior dislocation of right elbow joint after removal of plaster fixation, which immobilized joint for one month. This case report was made during my professional practice in C.L.P.A. in Prague, Vysočany, and in term 9. 1. - 3. 2. 2012 under the supervision of physiotherapist Mgr. František Vaňous. In thesis is processed complete input and output kinesiology analysis, description of process of each therapy unit and...
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Case Study of Physiotherapy Treatment of a Patient after Arthroscopic Bankart Repair
Bertron Simpson, Desiree Ginger ; Stupková, Michaela (advisor) ; Damborová, Martina (referee)
Author: Désirée Ginger Bertron-Simpson Title: Case Study of Physiotherapy: Treatment of a patient after Arthroscopic Bankart Repair. Objectives: This thesis is divided in two general parts. The first one consists of overviewing the shoulder anatomy, kinesiology, and biomechanics. The patient's diagnosis is also presented, including the underwent surgery. The second part presents the case study, with respective examinations provided, treatments and results after providing all the therapies. Clinical findings: The patient is a 16 years old female rugby athlete, 5 weeks after undergoing an Arthroscopic Bankart repair, performed on the 18th of December 2019 on her right shoulder. Her range of motion is limited in all directions with slight muscle atrophy around her right deltoid area, movement pattern in abduction is altered, constant hypertonicity on the upper trapezius area, bilaterally. Methods: All examination and treatment are based of the knowledge I have acquired in the Faculty of Sport and Physical Education of Charles University, in Prague. These include postural examination, ARoM and PRoM, muscle length and strength test, PIR, joint mobilization, soft tissue techniques, and physical activity programs adapted the patient's need. The goals of the therapies are to control existing range of...
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Differential equations in models of motion of dislocations
Vydrová, Jana ; Řehák, Pavel (referee) ; Šremr, Jiří (advisor)
This thesis deals with the differential equation which appears in the mathematical model by thermally activated motion of dislocations. It’s focused on screw dislocations in bodycentred cubic metals. Especially solves derivation of the pertinent differential equaiton and then explores properties of their solutions. To research these properties are used knowledges and techniques of qualitative theory of differential equations.
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Thermodynamics of Dislocation Pattern Formation at the Mesoscale
Gröger, Roman
We introduce a mesoscopic framework that is capable of simulating the evolution of dislocation networks and, at the same time, spatial variations of the stress, strain and displacement fields throughout the body. Within this model, dislocations are viewed as sources of incompatibility of strains. The free energy of a deformed solid is represented by the elastic strain energy that can be augmented by gradient terms to reproduce dispersive nature of acoustic phonons and thus set the length scale of the problem. The elastic strain field that is due to a known dislocation network is obtained by minimizing the strain energy subject to the corresponding field of incompatibility constraints. These stresses impose Peach-Koehler forces on all dislocations and thus drive the evolution of the dislocation network.
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