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Linear elastic fracture mechanics and its application on study of composed materials
Dohnalík, Petr ; Ševeček, Oldřich (referee) ; Máša, Bohuslav (advisor)
The main objective of this bachelor thesis is the introduction to computational methods of fracture parameters of the crack, which terminates at the bi-material interface. The preface of the work deals with composites, where possible crack can grow in materials with different elastic properties. In this part advantages of composite materials are closely described and usual structure arrangements of the components are presented. The next part of this work is focused on the linear elastic fracture mechanics and available concepts for assessment of the body with presence of the crack in the homogenous material are described. These concepts are based on analytical expressions and, also, on numerical methods. This problem is furthermore extended in the next chapter by case, when the crack terminates perpendicularly to the bi-material interface. Here are given procedures, which can provide information about the further crack behaviour. In practical part all presented procedures have been used in order to evaluate the crack parameters in the homogenous material and for the crack terminating at bi-material interface. Necessary calculations were performed using the finite element method implemented in the commercial system ANSYS. Calculated results were compared and closely discussed in the conclusion.
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Software for an estimation of residual fatigue lifetime of mechanical parts with crack
Motyka, Jakub ; Náhlík, Luboš (referee) ; Pokorný, Pavel (advisor)
This bachelor thesis deals with the creation of software for determining the residual fatigue time of mechanical parts with a crack. In the calculation of the lifetime of fatigue-stressed parts, the existence of an initial crack is assumed. During the operating load of the part, the crack may grow up to a critical size, when a sudden fracture of the part occurs. Knowledge of the number of residual loading cycles is important for machine design and safe part-operation. The first part of this thesis deals with linear-elastic fracture mechanics which forms the theoretical basis of the calculation software. The second part is devoted to the software itself, its principles and work in user interface. The last part compares the software-acquired results with the results reached analytically.
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Elastic Analysis of Crack Stability under Shear Loading Modes
Žák, Stanislav ; Profant, Tomáš (referee) ; Horníková, Jana (advisor)
The main goal of this thesis is to create a numerical simulation of a real experiment for specifying the ultimate state of spread of fatigue crack in pure shear stress modes and to deal with results of simulations for different specimen geometries. The simulations emulate real conditions of the experiment within the frame of linear elastic fracture mechanics. The first part of this work discusses a number of approaches to describe the stability and behaviour of cracks. The second part of this thesis deals with several possibilities of calculating crack characteristics employing ANSYS software. The third and most comprehensive part of the thesis describes the experiment which served as the template for the calculations. In addition, the setup of the simulations and the post-processing of the results for different crack parameters are discussed.
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Mechanical fracture parameters of concrete after exposure to high temperatures
Bejček, Michal ; Keršner, Zbyněk (referee) ; Šimonová, Hana (advisor)
The diploma thesis is focused on the evaluation of mechanical fracture parameters of concrete after exposure to high temperatures. In the introductory theoretical part general principles of fracture mechanics with the concentration on a linear elastic fracture mechanics and non-linear fracture models for the concrete are summarized. The meaning of the three-point bending fracture test used for determination of fracture parameters is also explained. Further the influence of high temperatures on the partial components of concrete and general modeling of temperature loading is described. The practical part is concerned with the evaluation of fire experiments on the concrete panels including numerical simulations using GiD and ATENA software. The evaluation of data obtained from the three-point bending test carried out on specimens with initial stress concentrator taken from concrete panels is a main part of the diploma thesis. The values of modulus of elasticity, effective fracture toughness, work of fracture and fracture energy are determined from the measured F–d and F–CMOD diagrams after their proper corrections in the GTDiPS application. The evaluation of the selected mechanical fracture parameters was performed by StiCrack software using effective crack model and work of fracture method and DKFM_BUT software using the double-K fracture model. Finally, the attention is paid to the analysis of the obtained data.
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Modeling of fracture process in quasi-brittle materials
Klon, Jiří ; Eliáš, Jan (referee) ; Veselý, Václav (advisor)
This work is focused on the evaluation of the selected fracture parameters of quasi-brittle material, especially concrete, and an assessment of their dependence on the size and shape of the fracture process zone developing at the tip of the macroscopic crack during fracture. For this purpose, experimentally obtained loading diagrams published in the scientific literature have been utilized. These diagrams have been processed into a form enabling creation and calibration of numerical models of these tests in the ATENA FEM program. The results obtained from simulations of the three-point bending tests on beams of four sizes, with three notches lengths, using the created numerical models were used for determination of fracture parameters of concrete. Results of the work consist of the determined values of the specific energy dissipated for creation of new surfaces of the effective crack and an estimation of the specific energy dissipated in the volume of the fracture process zone, which exhibits specific parameters for each beam size and notch length.
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DAMAGE OF COMPOUND STRUCTURES CAUSED BY MATERIAL DISCONTINUITY
Korbel, Jakub ; Žmindák, Milan (referee) ; Hutař, Pavel (referee) ; Knésl, Zdeněk (advisor)
This Ph.D. thesis deals with modeling of compound structures containing defects such as cracks or notches. Attention was mainly focused on structures manufactured out of metals and polymers. Presented results were obtained from experimental measurements, which were compared with theoretical estimations of the ultimate states of the compound structures. Theoretical estimations were obtained by the application of the generalized fracture mechanics, whose integral part is based on numerical solution provided by finite element method. The results of the Ph.D. thesis contribute both to prediction of the limit states of compound objects, and to verification of the validity of the generalized fracture mechanics.
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NUMERICAL STUDY OF UNIVERSAL BEAM (I SECTION) UNDER BENDING LOAD WITH CRACK
Morán, Alvarez J. ; Seitl, Stanislav ; Miarka, Petr
The structural components often contain cracks as a results of applied load. Therefore, these cracks must be studied how they affect the structural behavior and the total service life-time of the component. Bearing beams of the bridges have usually cross-section in the shape of an I-profile. In this contribution, a numerical parametric model was made in order to study the influence of the crack length, Poisson's ratio and web thickness on the stress distribution in the structural element, for which a three-point bending specimen was applied. The model is based on the linear elastic fracture mechanics (LEFM), with focus set on the determination of the stress intensity factor, as it is one of the main parameters used in the description of the stress fields in vicinity of the crack tip.
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Fatigue life prediction models
Hurta, Filip ; Vaněk, František (referee) ; Sladký, Martin (advisor)
Evaluation of fatigue is essential for determining operational capabilities of mechanical parts. Principles of material fatigue are discussed in this bachelor thesis. Most attention is paid to linear elastic fracture mechanics and variable amplitude loading. There are mathematical models, that describe conditions in the center of damaging. In the text there are described chosen models based on fracture mechanics. On basis of the conducted research, a computer program was developed, solving a crack growth in a specimen, depending on the defined loading. This program does not consider interaction effects during the loading sequence. Program output validation was performed by comparison of given results with the calculation and tests results from the literature. The data correlate with the non-interaction predictions, but comparison with the reality demonstrates the importance of interaction effects in complex loading.
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ANALYSIS OF MIXED MODE I/II FAILURE OF SELECTED STRUCTURAL CONCRETE GRADES
Miarka, Petr ; Šejnoha,, Michal (referee) ; Hutař,, Pavel (referee) ; Seitl, Stanislav (advisor)
The presented thesis is devoted to the experimental and numerical analysis of concrete fracture under the mixed-mode I/II load. This phenomenon was analysed on various concrete grades and types which are used in the fabrication of precast concrete structural elements. Subsequently, the Brazilian disc test with central specimen was used in experimental and numerical parts. The numerical part employs both linear elastic fracture mechanics (LEFM) approach and non-linear material model to assess the concrete fracture and failure under the mixed mode I/II load. The LEFM part is dedicated to evaluation the geometry functions and higher order terms of the Williams’ expansion, while the non-linear analysis is dedicated to crack initiation and propagation throughout the specimen using the concrete damage plasticity model. The experimental part is dedicated to the analysis of the mixed mode-mode I/II fracture resistance by the generalised tangential stress (GMTS) criterion with focus set on the governing role of the critical distance rC. Furthermore, the experimental part validates the applicability of the Williams’ expansion on the concrete. For this, experimentally measured displacements by digital image correlation technique were used to calculate the Williams’s expansion terms. Lastly, the thesis deals with the influence of the aggressive environment on the material’s fracture toughness and on the fracture resistance under the mixed mode I/II has been studied.
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Mechanical fracture parameters of concrete after exposure to high temperatures
Bejček, Michal ; Keršner, Zbyněk (referee) ; Šimonová, Hana (advisor)
The diploma thesis is focused on the evaluation of mechanical fracture parameters of concrete after exposure to high temperatures. In the introductory theoretical part general principles of fracture mechanics with the concentration on a linear elastic fracture mechanics and non-linear fracture models for the concrete are summarized. The meaning of the three-point bending fracture test used for determination of fracture parameters is also explained. Further the influence of high temperatures on the partial components of concrete and general modeling of temperature loading is described. The practical part is concerned with the evaluation of fire experiments on the concrete panels including numerical simulations using GiD and ATENA software. The evaluation of data obtained from the three-point bending test carried out on specimens with initial stress concentrator taken from concrete panels is a main part of the diploma thesis. The values of modulus of elasticity, effective fracture toughness, work of fracture and fracture energy are determined from the measured F–d and F–CMOD diagrams after their proper corrections in the GTDiPS application. The evaluation of the selected mechanical fracture parameters was performed by StiCrack software using effective crack model and work of fracture method and DKFM_BUT software using the double-K fracture model. Finally, the attention is paid to the analysis of the obtained data.
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