|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
Influence of Friction to the Shear Stress State in the Crack-Front Vicinity
Vlach, Jiří ; Hutař, Pavel (referee) ; Horníková, Jana (advisor)
The aim of this master thesis is to explore the influence of frictional forces to the stress and strain on the straight crack tip loaded in shear modes. The first section summarizes the most important things from the field of fracture mechanics. Especially theoretical knowledge about fracture parameters (stress intensity factor, J – integral) and their determination in computational environment ANSYS Workbench. The second part deals with computational modeling. At the beginning, is created the model of material, the model of geometry, the model of loads, etc. Then it is possible to solve the direct problem outlined in the introduction. A result of this thesis is the assessment of how the friction influences the fracture parameters in shear modes II and III.
|
|
|
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.
|
|
|
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.
|
guest ::
