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Analytical calculations of flange joints
Polišenská, Anna ; Chalupa, Aleš (referee) ; Hůlka, Jiří (advisor)
This Master’s thesis deals with flange joints. A suitably designed flange joint (FJ) construction and installation is necessary to ensure the reliability of piping systems and machinery where these joints are used. The thesis describes the procedures of their design and assessment in terms of tightness, strength and durability. It focuses on the stiffness calculation of all components of FJ – primarily the stiffness of flanges, bolts and seals. The main part of the work was to create a computational program by using the Python language to determine the appropriate preload force in the bolts. The program uses the procedures described in the ČSN EN 1591-1 standard. The thesis describes computational algorithms of this program, verification of the program and its use in the assessment of FJ on a specific technical work – pressure vessel with adjacent piping. Verification was performed by comparing the acting force to the seals obtained from the computational program and the stress-strain analysis using the finite element method (FEM), where the load model in this stress-strain analysis included the preload force obtained from the computational program. The application of the pressure vessel computational program consisted in determining the preload forces for all FJs of this assembly. The last part describes the assessment of the most loaded FJ. Again, stress-strain state was evaluated using FEM and FJ was assessed for tightness, strength and durability using the NTD A.S.I. standard.
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Computational simulation of machining
Zvěřina, Martin ; Hůlka, Jiří (referee) ; Petruška, Jindřich (advisor)
This Master’s thesis process list of different finite element programs, which allows us to simulate process of material separation. We estimated their advantages and disadvantages in the end. In program ANSYS Ls-Dyna was created 3D model, in which we simulate process of orthogonal splinter machining and we study dependence of changes different input parameters (tool geometry, depth of cut, cutting speed) on the chip form and forces rate between tool and workpiece.
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Computational prediction of material damage in forming
Kunc, Vítězslav ; Hůlka, Jiří (referee) ; Petruška, Jindřich (advisor)
The purpose of this thesis is to deal with the initiation of chevron cracks in forward extrusion. Using numerical simulation, the ability of selected fracture models which prognosticates the initiation of chevron cracks is observed. The influence of process parameters is studied (friction, reductions in cross section and angles of reduction) on the initiation and diffusion of damage. Solutions was executed by Abaqus for material 12 050.
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Analysis of Circular Bars Shearing Process
Dohnalová, Eva ; Hůlka, Jiří (referee) ; Foret, Rudolf (advisor)
In these days customers require a high quality as well as precision of products together with a cost that is as low possible. The cost of products can be reduced in a way of batch production. Implementation of the batch production requires a detailed plan of a technological process to avoid making depreciated products or series of products. A software package can be used to simulate the technological process of shearing to avoid difficulties of particular technological process. This bachelor paper contains analysis of technological process of shearing of circular section rods. The results of the analysis are going to be included in FEM simulations. The effect of the technological process of shearing on material was determined by optical and scanning electron microscopy method. The microhardness measurement was used to analyse the deformation hardening of the examinated material.
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Small-punch test of structural steels at low temperatures
Němčíková, Eva ; Hůlka, Jiří (referee) ; Hadraba, Hynek (advisor)
Diploma thesis is focused on comparison of small punch test results and tensile test results. For experiments were chosen steel P91, 10Ch2MFA, 20CrNi2MoV, 11 416 and 42 2707. These steel are used in nuclear power engineering, or they were developed for this purpose. Basic mechanical characteristics, namely ultimate tensile stress and yield stress, were evaluated from small punch test records of observed materials. This is done via convenient correlation relationships. Obtained values were compared with values obtained by conventional tensile tests. There are mentioned own suggested correlation relationships and comparison of temperature curves gained from small punch test and tensile test in the thesis. Assessment of microstructure of observed materials and analysis of fracture surfaces was provided as well. It was found out, that for assessing basic mechanical characteristics (ultimate tensile stress and yield stress) is the best to suggest own correlation relationships, instead of using universal relationships from literature. The fracture mechanism of all types of assessed steel was ductile in entire temperature range (up to -40 °C).
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Evaluation of the flange joints calculations approaches
Jeník, Ivan ; Chlud, Michal (referee) ; Hůlka, Jiří (advisor)
This bachelor´s thesis deals with the design and assessment of flange joints with gasket. The first part defines term flange joint and its load. It surveys and assesses the possible alternatives of design solution. Mentioned is the issue of bolt connections with pretension, including force relations in the joint, determination rigidity of parts and their strength. In addition, analysis of the causes of bolts failures and their removal, methods of creating pretension. It gives an overview of the most widely used types of gaskets, their properties, application and definition of characteristic values of gaskets and their determination according to ČSN EN 13 555. Another section deals with the design process of flange joints, standards for the design, desired outputs and assesses analytical and numerical approach. Computational program was created in MS Excel 2007 for design calculation of flange joints according to ČSN EN 1591-1. Verification of the results was performed with calculation of identical models using finite element method (FEM) in ANSYS Workbench 14.0. Errors in standards formulas were submitted. In conclusion, the results obtained analytically and by FEM were assessed for a specific load conditions of gate valve DN 300. Camprofile (grooved) gasket with nonlinear material model was used.
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Application of ductile fracture models in computational simulation of manufacturing operations
Hůlka, Jiří ; Houfek, Lubomír (referee) ; Petruška, Jindřich (advisor)
This diploma thesis is an introduction to the ductile fracture under large plastic deformations and is focused to numerical simulation of this type of problems. Explicit finite element method (FEM) is discussed in theoretical introduction as the most powerful tool for numerical calculations in this area. Actual state of research and possibilities of ductile fracture simulations are presented. Applicable fracture criteria are collected in a summary sheet and the most important ones are selected and commented in detail. The problem of implementation of selected criteria into commercial FEM packages is discussed, too. Main part of the work is presented in chapters 7÷9 where two ductile fracture criteria (Equivalent Fracture Strain and Johnson-Cook) are applied to numerical simulation of material cutting. All results were obtained with ABAQUS/Explicit 6.5.1 and their verification was realized by experimental measurement.
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Low cycle fatigue research and application in nuclear industry
Sehnal, Dominik ; Kuželka, Jiří (referee) ; Hůlka, Jiří (advisor)
Fatique life extension of nuclear powerplants lies in the search for project reserves. This work deals with the evaluation of low-cycle fatigue of nuclear installations of the VVER type and the assessment of the influence of the computational model level. Fatigue tests of austenitic steel using optical method of digital image correlation for which the evaluation procedure is designed and used is performed. Selected model of plasticity with kimenatic (Chaboche) and combinated hardening (Chaboche, Voce) are calibrated from the obtained data. Subsequently, the durability of the test specimen is determined by computational modeling for different material models. From the comparison of the results of fatigue tests with the calculation, the material models suitable for the description of fatigue life and their validity are determined.
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Computational Prediction of Ductile Fracture
Hůlka, Jiří ; Španiel, Miroslav (referee) ; Žmindák,, Milan (referee) ; Petruška, Jindřich (advisor)
The issue of ductile damage prediction can be generally divided in two types of tasks. The first one is to preventing the initiation of ductile damage with is most common group of calculation today. The second task can be described as aimed damaging, such as machining, cutting, etc. The significant development of this issue occurred in recent decades by help of development and access to powerful computational techniques and new experimental possibilities. However, the behaviour of ductile damage at multiaxial proportional and non-proportional loading is insufficiently described. This thesis helped to clarify some of the unknown this topic. It contributed to the understanding of selected materials behaviour at room temperature and quasistatic loading. Austenitic stainless steel AISI 316L was selected for detail study of ductile damage. A large number of experiments were performed on this material, such as uniaxial tensile tests of smooth and notched specimens, upsetting tests of smooth cylinder and special cylinder with dimple, butterfly specimens, notched tube specimens and penetration tests. Experimental results is used for calibration of five so-called simple criteria, taking into account fracture strain and stress triaxiality (Equivalent fracture strain, Johnson-Cook, simplify Bao-Wierzbicki, RT, RTCL) and universal criteria (Bai-Wierzbicki, Xue-Wierzbicki, EMC, LOU, KHPS). SPT potentially enable the determination of actual mechanical behaviour using only a fraction of specimen volume compared to standard specimen. It is promising tool to improve accuracy when assessing working life of components in operation. The inverse numerical simulation loop of SPT was designed using program OptiSLang on the basis of detailed sensitivity analysis. It was achieved 2% deviation of yield strength and 6% deviation of ultimate strength obtained from tensile tests. A several modification of SPT specimen was suggested for universal criteria calibration of small material volume. The 3D numerical model was built for numerical simulation with ductile damage simulation. The criteria KHPS and EMC gave the most accurate results.
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