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Types of fatigue tests and methods of data processing
Lamrich, Richard ; Halabuk, Dávid (referee) ; Vosynek, Petr (advisor)
Bachelor thesis is focused on fatigue testing and creating of S-N curves. In the first part three main stages of fatigue life are processed in order of making theoretical knowledge needed. Next the thesis is focused on dividing methods for making these tests and machines that are used for these tests and shows under which circumstances they are appropriate to use. Last part is dedicated to methods of creating of S-N curves.
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Determination of residual stresses from strain field around drilled hole
Horák, Richard ; Návrat, Tomáš (referee) ; Halabuk, Dávid (advisor)
The master’s thesis focuses on determining homogeneous residual stresses using the hole-drilling method. The optical method of digital image correlation (DIC) is used for measuring released strains. In order to evaluate residual stresses using the entire strain field, it is necessary to know the functional dependencies of calibration constants on this field. Therefore, a significant part of the master’s thesis includes finding these dependencies in relation to the dimensions of the drilled hole and coordinates of the measured points. Another part of the thesis deals with the evaluation of homogeneous residual stresses based on provided experimental data obtained from the measurement of uniaxially loaded steel flat bar with a through-hole. At the end of the thesis, a sensitivity analysis is performed, which examines the influence of input variables in the calculation algorithm in relation to computed residual stresses.
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Detection of infill defects in 3D printed structures using the DIC method
Doležal, Tomáš ; Halabuk, Dávid (referee) ; Ščerba, Bořek (advisor)
Additive manufacturing offers wide range of advantages. However various internal defects are likely to be formed during the manufacturing process which negatively affect mechanical properties. Detection of those defects is critical to ensure that the manufactured component stays reliable and maintains its dependability throughout its whole life. The potential of the digital image correlation (DIC) method for detect detection in components manufactured using additive technologies has not yet been investigated in the literature. In this master thesis a novel non-destructive defectoscopic method for the internal defect detection in 3D printed structures is presented, based on the evaluation of the strain field obtained by the DIC method. The method was experimentally evaluated on samples with artificial internal defects fabricated by FDM technology. The samples containing defects were successfully visually detected. A convolutional neural network was then used for the defect detection and achieved a classification accuracy of 94,5 %. This methodology has a potential to provide cheap and fast detection of internal defects formed in additive manufactured components in the future although future research is still required.
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Numerical simulation of the hole drilling method for residual stress measurement
Halabuk, Dávid ; Ganev, Nikolaj (referee) ; Pástor,, Miroslav (referee) ; Návrat, Tomáš (advisor)
The doctoral thesis is focused on the investigation of various cases that may occur in the measurement of residual stresses by hole-drilling method and which deviate from the ideal state for which hole-drilling method is derived. In order to assess various stress states, geometries or material properties of the measured body, a computational model simulating the hole-drilling method was created by the finite element method. The first investigated case deals with cylindrical bodies and errors that may occur when the hole-drilling method is used to measure residual stresses in bodies with various surface radii. In addition to the evaluation of errors for different stress states, a procedure for the calculation of uniform residual stresses in cylindrical bodies has been proposed. The next part of the thesis is focused on investigating the influence of the residual stress placed in the perpendicular direction to the measured surface on the error of evaluated residual stresses located in a plane parallel to the surface of a measured body. The last and largest part of the thesis deals with cases in which plastic deformations form in the area around the drilled hole during residual stress measurement. After examining of various parameters influencing the formation of plastic deformations, a correction procedure which is capable to correct the uniform residual stresses for various hole diameters and various strain gauge rosettes independently of the stress state or material properties was proposed. The proposed correction procedure was thoroughly tested to ensure its satisfactory results. Based on the obtained results published in this thesis, it is possible to estimate the influence of various conditions deviating from the ideal case on the accuracy of the evaluated residual stresses and in some cases minimize this influence by the proposed procedures.
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Finite element solution of axially loaded bars using quadratic element
Janáčik, Lukáš ; Halabuk, Dávid (referee) ; Vaverka, Jiří (advisor)
This bachelor thesis describes an algorithm for programming finite-element model with quadratic elements for axial loaded bar. In the introduction, we define the basic concepts of mechanics of materials, which are used in this thesis and are necessary to understand problems, for which finite element method was formulated. The thesis clarifies a transition from basic differential equation to weak formulation, which is the base of finite element method. We define element matrices and describe transition to global matrices, relating to the whole body. Then describe implementation of boundary conditions and postprocessing of the results, necessary for calculation and displaying of other unknowns. In the practical part, 3 illustrative problems are presented and calculated numerically in FEM solver using Matlab, analytically and in software ANSYS Workbench. Results are then compared and evaluated. Problems have different boundary conditions (linear axial load, tempered cross section, statically indeterminate fixation). Results of displacement and normal stress for programmed solver are identical to those from Ansys (using the same settings) and analytical solution (after more elements are added, if necessary). Problem with tempered cross section was simulated in Ansys using plain stress, because the program can’t define bar with tempered cross section. This revealed sheer stress contained in parts of cross section further from centreline, which are not calculated in our FEM solver and in some cases might be significant.
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Optical measurement of crack length utilizing the DIC method
Dziubek, Jan ; Halabuk, Dávid (referee) ; Ščerba, Bořek (advisor)
The thesis deals with the measurement of crack length using digital image correlation. The theoretical part of the thesis presents the method of digital image correlation, crack problems, and also introduces conventional methods for measuring crack length. There are currently no universal procedures in the field of crack length measurement using DIC. Different authors have only proposed different procedures to find the crack tip. Three different methods are used to determine the crack length using digital image correlation. Use of the edge detection method in the displacement field, the inflection point search method and the deformation threshold method. The aim of this work is to describe and compare these approaches.
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Stress-strain analysis of a crane arm
Mora, Lukáš ; Halabuk, Dávid (referee) ; Fuis, Vladimír (advisor)
The content of this bachelor’s work is a summarization of types of tower cranes and subsequent stress-strain analysis of the crane arm of the crane type 150EC-B8 Litronic located on the Šumavská street in Brno. Analytical stress-strain analysis is calculated with equations of equilibrium using joint method in various types of loading of the construction with MAPLE software. Numerical calculation is executed on 3D model of the construction in software ANSYS. The aim of this bachelor work is the verification of the correctness and comparison results of analytic calculation with numeric calculation and evaluation of the results from a limit states and deformation standpoint.
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Using free programs for topology optimization on selected problems in solid mechanics
Flídr, Ondřej ; Halabuk, Dávid (referee) ; Vosynek, Petr (advisor)
This bachelor thesis examines open-source software for topology optimization, analyzes their possibilities on selected problems of solid mechanics and verifies the results by the finite element method. The theoretical part describes the principles and methods by which the tasks of topology optimization can be solved. This is followed by search for open-source software using these methods. The calculation process in selected software is described in detail in solving sample tasks in the penultimate part. In the last chapter, the best open-source software are compared with each other and also with commercially distributed Ansys Workbench 19.2. The output is an evaluation of the usability of individual open-source software in industry. This thesis can also serve as a manual for using selected programs for inexperienced users.
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