|
|
Development of Models of Al Alloys Behaviour for Applications in Numerical Simulations of Welding and Heat Treatment
Vaněk, Mojmír ; Věchet, Stanislav (referee) ; Neumann, Heinz (referee) ; Daněk, Ladislav (advisor)
The thesis deals with methodology for computational approaches for numerical simulations of welding and heat treatment of aluminium alloys. The thesis describes improvement of the current methodology for metallurgical part of the numerical analysis of welding, which is important mainly for prediction of dimensions of the heat affected zone (and deformations). The improvement was carried out based on CHD diagram that describes precipitation and dissolution of phases during continuous heating. The thesis also describes carried material measurements (measurement of chemical composition, dilatometric tests, tensile tests of several conditions of materials at temperatures up to 500 °C and measurement of aging curves), which allowed to significantly refine analysis results for the alloys EN AW-5083 and EN AW-6082. Based on an evaluation of the measurements, several conclusions were made. They can be useful for creation of material databases of other aluminium alloys. The thesis also describes quantification of dependence between tensile strength and yield strength on the Vickers hardness for different conditions of EN AW-6082. There is also methodology for numerical simulation of the heat treatment process of heat treatable Al alloys in the dissertation. The methodology is completely new approach which has never been published so far. Application of this method is based on user changes of the material database in software Sysweld after relatively easy measurement of aging curves. Therefore, the methodology can be considered as promising for application in industrial practice.
|
|
|
Fatigue-creep interaction in Ni superalloys and TiAl alloys
Šmíd, Miroslav ; Věchet, Stanislav (referee) ; Kunz, Ludvík (referee) ; Obrtlík, Karel (advisor)
The present doctoral thesis is focused on the effect of dwells on the low cycle fatigue behaviour of advanced high temperature materials. 10 minutes strain holds are introduced into the cyclic straining of cast Ni-based superalloy IN792-5A and cast intermetallic alloy TiAl-7Nb which were chosen as experimental material. Fatigue experiments were conducted in strain control mode with constant total strain amplitude and strain rate. IN792-5A was subjected to continuous cyclic loading test as well as fatigue tests either with tensile peak strain holds or compressive peak strain holds at temperature 800 °C. TiAl-7Nb was experimentally examined by continuous cyclic loading tests and also by fatigue test with tensile peak strain hold times at temperature 750 °C. Cyclic hardening/softening curves, cyclic stress-strain curves, Manson-Coffin curves and Basquin curves were obtained. Stress relaxation data were measured during hold times. Mean stress evolution was observed and documented. Microstructure of both alloys was observed in as-received state and also after cyclic loading by means of SEM and TEM. Surface relief investigation revealed cyclic plastic strain localisation as well as fatigue crack initiation sites. Fatigue crack propagation was described using fracture surface and longitudinal gauge section observations. Dislocation structures developed in the course of fatigue tests were studied and documented.
|
|
|
Micromouse II mobile Robot
Pavláček, Martin ; Věchet, Stanislav (referee) ; Marada, Tomáš (advisor)
This thesis describes the design and implementation of mobile robot IEEE Micromouse category. The aim is to build a functional design of robot usable to testing methods of mapping and localization. The thesis also deals with the design of electronics for motion control. Electronic design of optical sensors operating on the principle of reflection of infrared light and the signal processing.
|
|
| |
|
|
Materials for atypical constructions of bicycle frames
Motl, Daniel ; Věchet, Stanislav (referee) ; Němec, Karel (advisor)
Bachelor’s thesis deals with materials for atypical bicycle frames. At first goes to history of generally bicycles. After gives definition what atypical bicycle is and includes four practical examples this type of bicycle which was real manufactured. Next step is about materials. Firstly about all types of materials uses in bicycles industry. Secondly the most suitable materials for atypical frames were choosen. In the end this materials were described in detail.
|
|
|
Design of autonomous mobile robot.
Vodrážka, Jakub ; Marada, Tomáš (referee) ; Věchet, Stanislav (advisor)
The thesis deals with design of the device for testing the localization techniques for indoor navigation. Autonomous robot was designed as the most appropriate platform for testing. The thesis is divided into three parts. The first one describes various kinds of robots, their possible use and sensors, which could be of use for solving the problem. The second part deals with the design and construction of the robot. The robot is built on the chassis of the differential type with support spur. Two electric motors with a gearbox and output shaft speed sensor represent the drive unit. Coat of the robot was designed for good functionality and attractive overall look. The robot is also used for the presentation of robotics. Thesis provides complete design of chassis and body construction, along with control section and sensorics. The last part describes a statistical model of the robot movement, which was based on several performed experiments. The experiments were realized to find any possible deviations of sensor measurement comparing to the real situation.
|
|
|
Micro-hydraulics system design
Pitaš, Martin ; Marada, Tomáš (referee) ; Věchet, Stanislav (advisor)
One of the main aims of presented bachelor's thesis is an implementation of hydraulic circuit by micro-hydraulics system. Bachelor's thesis has three main part. First part deals with hydraulic distribution and selection of acceptable devices of hydraulic circuit, especially their advantageousness in term of finance. Second part is devoted to the construction of fixation for the position sensor on linear hydromotor, holder for hydraulic valve and hydrogenerator. Third part describes to hydraulic circuit, right hydraulic oil for whole hydraulic circuit. The verifying calculation confirming rightness selection particular devices is here also. Autodesk Inventor Professional 2008 (chapter 3) a FluidSIM Hydraulics V 4.2 Demo Version English (chapter 4) was used as a general software.
|
|
|
Position control of servo with discontinuouns rechangeable speed
Jindra, Pavel ; Věchet, Stanislav (referee) ; Němec, Zdeněk (advisor)
Diploma thesis work includes simulation of compensation of control for discrete. The aim of the work is a solution positioning control of servomotor drive piston, which is controlled by pass of the pressure oil with the help of several electromagnetically controlled switchboards with the orifice in the output channels. The verification activities of the regulated system is done using simulation in Matlab/Simulink and Matlab/Simulink, Matlab/Hydrosim. The requirement on the created model is to verify the behavior of the system to be modified to be used for the further development of the issue
|
|
|
Initiation and development of cyclic damage in steel for the energy industry
Horník, Vít ; Mazal, Pavel (referee) ; Věchet, Stanislav (advisor)
The main content of this master's thesis is a determination of the fatigue properties by using non-destructive testing methods – the acoustic emission technique and the X-ray diffraction. The reactor steel, that is named GOST 15Ch2NMFA, is used as a model material and is used to manufacture VVER-1000 reactor pressure vessels. The supplied material was made of two different steel melting, designated as H and S. For the basic measurement of the fatigue properties the stress-cycle asymmetry R = -1 was used. Some of the samples were used for approximate determination of the fatigue strength stress-cycle asymmetry R = 0. During the loading process the resonance frequency of the loading machine and acoustic emission signals were recorded. The changes in microstructure were estimated from the record of acoustic emissions during the whole fatigue life. The change of the microstructure was experimentally observed by X-ray diffraction analysis. The mechanism of the fatigue can be described by the observation of the microstructural processes as well as the relevant bifurcation with sufficient sensitivity. The results of the used methods indicate a decay and re-growth of mosaic blocks during the whole loading process. Therefore, it is important to find a correlation of these two non-destructive methods, or to use other non-destructive testing methods in the future.
|
|
| |
guest ::
RSS feed.