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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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Advanced evaluation of selected fracture tests of fibre reinforcement concrete specimens
Majda, Tomáš ; Frantík, Petr (referee) ; Keršner, Zbyněk (advisor)
The goal of this thesis was evaluation of extensive series of selected three point bending tests on fibre reinforced concrete specimens of ages 7, 28 and 126 days. First the measured data were adjusted by GTDiPS software. Than the assumed contribution of fibres in load--deflection diagram was approximated by regressive function. Contribution of matrix was calculated by deducting the approximated part from full diagram. Using StiCrack software the Young modulus, fracture toughness and fracture energy were calculated for both original and approximated diagram. All results were evaluated and tabled.
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Physical and Mathematical modelling of Chimney Demolition
Ficker, Tomáš ; Keršner, Zbyněk (referee) ; Frantík, Petr (advisor)
The thesis deals with physical and numerical modelling of downsized model of chimney and its demolition. The properties of downsized physical model, which is made of wooden cubes, are being researched and experimentally tested. The physical experiments are then designed using software FyDiK. Numerical Model is simplified to 2D problem, whereas the problem includes dynamic effects. Conformity of designed software model and physical experiment is tested. The aim of this thesis is to achive the best possible conformity of physical and numerical models.
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Evaluation of fracture tests of selected concrete specimens
Součková, Markéta ; Lehký, David (referee) ; Keršner, Zbyněk (advisor)
This bachelor thesis deals with evaluation of fracture tests of selected concrete specimens. It is divided into two parts: theoretical and practical. The theoretical section describes fracture parameters, three point bending test and effective crack model. It explains evaluation process of the expriments step by step, too. The practical part contains charts with the resulting values of fracture parameters. The StiCrack software was used for analysis of fracture tests. The result of this thesis is comparison of influence the thength classes of concrete, age of specimens and place of ripen on the values of fracture parameters.
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Modeling of Elastic Mechanisms
Slaný, Jan ; Keršner, Zbyněk (referee) ; Frantík, Petr (advisor)
The thesis deals with constructing and solving a discrete mechanical model from the point of view of dynamics. As an example of a real-world problem which can be approximated in this way, the dynamical behaviour of a bow and arrow during loose have been chosen. In order to solve this particular type of model, a specialized piece of software has been developed. This method and software have been deployed to simulate shooting a straight bow of specific parametres. Two variants for the shape of the bowstaff have been evaluated.
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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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Chimney demolition modeling
Ficker, Tomáš ; Keršner, Zbyněk (referee) ; Frantík, Petr (advisor)
The thesis deals with solving of a discrete dynamic 2D model of a chimney during its demolition. Specific goal of the thesis is to clarify observed phenomenon that is a break of the chimney while falling. The model of the chimney is designed and solved using software FyDiK which is able to solve dynamic effects. For verification of results, two models of chimney have been designed.
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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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Experimental Verification of Optimal Shape of Beam
Uríček, Matúš ; Keršner, Zbyněk (referee) ; Frantík, Petr (advisor)
The thesis deals with design of beams of optimized shapes, which are than manufactured by 3D printer and their features are experimentally verified. When the limit strength of a given component is reached, ways of fracture development are observed. Information obtained from the experiments are then compared with assumptions generated by numerical methods.
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