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Extension of Discrete Model for Simulations of Ballistic Experiments
Fleischerová, Beáta ; Eliáš, Jan
During the ballistic experiments, fiber-reinforced concrete panels are loaded by a high-velocity projectile. The meso-scale discrete model built in programming language C++ is used to simulate these tests. The mechanical behavior of short fibers crossing a single crack is derived and implemented. The explicit time integration scheme is under development to replace the current implicit solver utilizing the generalized-alpha method. The paper presents some partial results.
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Circular Representative Volume Element for Homogenization of Discrete Model of Concrete
Středulová, Monika ; Eliáš, Jan
The contribution presents initial results obtained by employing a circular representative volume element (RVE) for the homogenization of a discrete model of concrete. Based on initial research, circular RVE might be a promising alternative to the classical square one (for 2D problems), especially considering its use in conjunction with periodic boundary conditions after strain localization in the material. The contribution shows the behaviour of the circular RVE in elastic loading and compares it to the results obtained by the usually used square RVE.
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Methods of Static Buckling Analysis
Svoboda, Filip ; Eliáš, Jan (referee) ; Frantík, Petr (advisor)
The aim of this theses is to create application, which is able to calculate buckling load of structure made from 1D bar elements, using finite element method. introduction is devoted to basic principles of buckling and derivation of necessary formulas. Then are described all operations and numerical methods needed for the application. At the and is in detail analyzed few structures and results are compared with known solutions or with other applications.
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Steel Beam Structure Optimization
Lamoš, Radek ; Eliáš, Jan (referee) ; Frantík, Petr (advisor)
The main subject of this work is to find ideal solution of the steel frame structure and offer the best solution to investors. The aim is to get know how steel structures works, write down internal forces when parametres are changing. Parameters can be profiles, loads or many others. The output should be perfectly optimized construction. The content combines theory of structural mechanics and designing steel structures. This project could be very useful in practice designing of steel frame structures with the possibility of expansion by other parameters.
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Crack path calculation using linear elastic fracture mechanics
Bónová, Kateřina ; Malíková, Lucie (referee) ; Eliáš, Jan (advisor)
This diploma thesis deals with the different possible calculations of crack path. Specifically, it focuses on criteria based on maximum tangential stress, minimal strain energy density, crack tip displacement, and local symmetry. These criteria are used for calculations in ANSYS software to estimate possible crack paths on four simple structures. The thesis also contains the codes created in ANSYS. Using these, the crack trajectory of a given structure can be calculated by any of the four criteria described.
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Integration of microstructure informed enrichment base functions
Ladecký, Martin ; Zeman,, Jan (referee) ; Eliáš, Jan (advisor)
This thesis deals with problems related to the numerical integration of rapidly oscillatory functions. Analyze classical methods of numerical integration and compare them with method published by David Levin\cite{levin82}. Levin's method is applied in solving Laplace differential equation that describes deflection of membrane. To solve potential problem is used hybrid finite element method with Trefftz bases functions.
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Comparison of localization limiters for strain-softening
Květoň, Josef ; Vořechovský, Miroslav (referee) ; Eliáš, Jan (advisor)
It is well known, that simulation of crack propagation using the finite element method is dependent on mesh discretization. The thesis compares two approaches, that are designed to reduce the mesh influence: (I) the crack band model and (II) the nonlocal model. These localization limiters are applied to simulate three-point-bent beam with and without notch. The model of the beam is made with several variants of mesh discretization differing in finite element size and inclination. Performance of both localization limiters is discussed.
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Machine learning applied to simulations of material mechanical behavior
Raisinger, Jan ; Novák, Lukáš (referee) ; Eliáš, Jan (advisor)
The thesis explores the possibility of using machine learning models to predict effective macroscopic material parameters of multiphase materials. The asymptotic expansion homogenization method is used together with the finite element method to create software in Python, which is used to calculate effective macroscale mechanical parameters of sets of heterogeneous arrangements. These sets are generated using several methods, e.g. as a realization of a discretized random field. The sets are used to train neural networks built using the Keras library. The accuracy of the networks and the quality of training data are assessed. The advantages and disadvantages of the networks compared to the FEM solver are demonstrated on their application in an optimization problem.
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Probabilistic discrete model of concrete fracturing
Kaděrová, Jana ; Lehký, David (referee) ; Konečný,, Petr (referee) ; Eliáš, Jan (advisor)
The thesis presents results of a numerical study on the performance of 3D discrete meso–scale lattice–particle model of concrete. The existing model was extended by introducing the spatial variability of chosen material parameter in form of random field. An experimental data from bending tests on notched and unnotched beams was exploited for the identification of model parameters as well as for the subsequent validation of its performance. With the basic and the extended randomized version of the model, numerical simulations were calculated so that the influence of the rate of fluctuation of the random field (governed by the correlation length) could be observed. The final part of the thesis describes the region in the beam active during the test in which the most of the fracture energy is released in terms of its size and shape. This region defines the strength of the whole member and as shown in the thesis, it does not have a constant size but it is influenced by the geometrical setup and the correlation length of the random field.
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Analysis of crack propagation using J-integral
Bónová, Kateřina ; Květoň, Josef (referee) ; Eliáš, Jan (advisor)
The bachelor thesis is focused on importance and application of J-integral in crack propagation analysis. J-integral is a method of fracture mechanics used to determine the strain energy release rate. In other words it provides the amount of energy available for crack propagation in elastic and elasto-plastic materials. The thesis presents derivations of relations between J-integral, crack driving force and stress intensity factor. The most important contribution of this thesis is detailed analytical calculation of the J-integral on simple structures. The results are verified by numerical models in ANSYS.
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