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Basic features of aggregate-matrix-interface fracture of concrete: pilot modelling
Vyhlídal, M. ; Šimonová, H. ; Veselý, V. ; Keršner, Z. ; Klusák, Jan ; Malíková, Lucie
In this paper, the attention is paid to investigation of the importance of the Interfacial Transition Zone (ITZ) in concrete for the global fracture behaviour. A simplified cracked geometry (consisting matrix, ITZ and aggregate) is modelled by means of the finite element method with a crack terminating at the matrix-ITZ interface. Numerical studies assuming two various ITZ thicknesses and several various ITZ elastic moduli are performed. Based on the values of the opening stress ahead of the crack tip (its average value and stress range) a few conclusions are discussed. The pilot analyses dealing with the effect of ITZ on the stress distribution should contribute to better description of toughening mechanisms in silicate-based composites.
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Assessment of Crack Stability in a Quasi-brittle Particle Composite
Malíková, Lucie ; Klusák, Jan ; Keršner, Z.
Fracture behaviour of a crack in a particle (silicate based) composite is studied. The crack propagation depends not only on mutual elastic mismatch of matrix and aggregate but also the influence of the interfacial transition zone (ITZ) between the matrix and the aggregate is discussed. Various combinations of materials and geometry of matrix, aggregate and ITZ can improve or degrade fracture properties of the composite. Extensive numerical simulations on a basic 3-point-bending cracked specimen via the finite element method are performed in order to analyze the stress field near the crack tip. Linear elastic fracture mechanics approach is utilized in order to assess the crack stability and summarize several conclusions.
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Simulation of Idiofonic System
Múčka, Martin ; Keršner, Zbyněk (referee) ; Frantík, Petr (advisor)
The thesis deals with dynamic simulation of real bell behavior over time. The model is created according to principles of physical discretization as a spring in the FyDiK3D software. In order for the model to be declared as relevant, it is necessary to prove the behavior of the structures used in the elementary tasks of the mechanics. It shows the correlation between the stiffness of normal and diagonal springs. Describes how to use software import tools to create a model. The resulting model approaches its real bell behavior.
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Analysis of selected silicate based composites volume changes
Kubeš, Pavel ; Šimonová, Hana (referee) ; Keršner, Zbyněk (advisor)
This diploma thesis deals with the analysis of volume changes of selected silicate based composites. The first part introduces the issue of volume changes of concrete, especially the shrinkage process, two selected models for shrinkage prediction, describes configuration and course of performed tests, as well as the processing of measured experimental data. The second part contains input data modified by the program GTDiPS and another calculated parameters. The result of the work is the evaluation of the influence of thermal dilation on the development of shrinkage of young concrete. Another output is the comparison of accuracy of the two selected prediction models to capture the course of measured shrinkage.
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Fracture of selected building composites in the vicinity of aggregate-matrix-interface
Vyhlídal, Michal ; Malíková, Lucie (referee) ; Keršner, Zbyněk (advisor)
The interface between aggregate grains and matrix in cementitious composites is their weakest element. The topic is particularly significant in the case of high performance and high strength concrete technology for which the eliminination or reduction of these weak links are necessary. The aim of this thesis is to determine the influence of the interface on the fracture behaviour of the cementitious composites. The fracture experiments were performed for this purpose and were complemented by the nanoindentation’s results and scanning electron microscopy results. Numerical model was created in ANSYS software on the basis of these data and the fracture toughness values of the interface were evaluated by means of the generalized fracture mechanics principles. Conclusion of the thesis is proof that the interface properties have a significant influence on the fracture behaviour of cementitious composites.
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Evaluation of fracture test of selected core-drilled cylindrical specimen
Halfar, Petr ; Sobek, Jakub (referee) ; Keršner, Zbyněk (advisor)
The diploma thesis deals with effective crack model for a cylinder specimen with an chevron-shaped notch, loaded by a three-point bending. The first part of the thesis is theoretical and the it describes the use of fracture mechanics for quasi-brittle materials – concrete and rocks. Furthermore there is described the linear elastic fracture mechanics and founding the geometry function for a different geometries of fracture tests. The second part describes the FEM program, which was used to calculate the fracture parameters, that were used to determine the length of the effective crack and how the program was tested before it was used. The last part describe calculations of fracture toughness by using the effective crack model on selected rock and concrete specimens.
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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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Possibilities of using X ray tomography for description of damage of temperature loaded concrete
Rozsypalová, I. ; Kumpová, Ivana ; Daněk, P. ; Šimonová, H. ; Keršner, Z.
The effect of high temperatures on concrete affects the internal structure of this composite material. The paper opens the question of the possibility of using a computed X–ray tomography to quantify the degree of damage of a concrete specimen that was drilled from the selected experimental panel loaded in a fire furnace with high temperatures at the AdMaS (Advanced Materials, Structures and Technologies) research centre at Faculty of Civil Engineering Brno University of Technology. The nominal value of the maximum temperature on the heated side of the panel was 1000 °C. Advanced workstation computer X–ray tomography TORATOM at Centre of Excellence Telč (CET) is parallel imaging of an object in two spectra of X–ray radiation, that allows to highlight differences between the material components to the full X–ray spectrum similar to the attenuation of the radiation.
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