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Verification of nonlinear material models of concrete
Král, Petr ; Němec, Ivan (referee) ; Hradil, Petr (advisor)
Diploma thesis is focused on the description of the parameters of nonlinear material models of concrete, which are implemented in a computational system LS-DYNA, interacting with performance of nonlinear test calculations in system LS-DYNA on selected problems, which are formed mainly by simulations of tests of mechanical and physical properties of concrete in uniaxial compressive and tensile on cylinders with applying different boundary conditions and by simulation of bending slab, with subsequent comparison of some results of test calculations with results of the experiment. The thesis includes creation of appropriate geometric models of selected problems, meshing of these geometric models, description of parameters and application of nonlinear material models of concrete on selected problems, application of loads and boundary conditions on selected problems and performance of nonlinear calculations in a computational system LS-DYNA. Evaluation of results is made on the basis of stress-strain diagrams and load-displacement diagrams based on nonlinear calculations taking into account strain rate effects and on the basis of hysteresis curves based on nonlinear calculations in case of application of cyclic loading on selected problems. Verification of nonlinear material models of concrete is made on the basis of comparison of some results of test calculations with results obtained from the experiment.
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Smoothed Particle Hydrodynamics in Structural Dynamics
Hušek, Martin ; Králik,, Juraj (referee) ; Maňas,, Pavel (referee) ; Kala, Jiří (advisor)
The focus of the thesis is on the application of the Smoothed Particle Hydrodynamics (SPH) method in structural dynamics with an emphasis on usage of quasi-brittle materials. The first part is focused on the introduction, history, and theoretical background of SPH. Numerical examples in which strengths and weaknesses of SPH are shown follow. In addition to pure SPH models, several coupling approaches with the Finite Element Method (FEM) are also discussed. After the introduction of SPH, the focus is on quasi-brittle materials and their reinforced variants. The numerical concept and mathematical background of the Continuous Surface Cap Model are outlined, several benchmarks are presented. Strain-rate effects and their impact on pure SPH and coupled SPH-FEM models are evaluated next. In this section, the author proposes a new approach for SPH models reinforcement with FEM beam elements. The coupling approach was named sublayer coupling and shows a potential in simulations while the SPH tensile instability is alleviated. Since concrete is often associated with heterogeneity and very specific material structure, a unique algorithm for concrete structure generation in combination with SPH is proposed in the next chapter. The concept is based on utilization of coherent noise functions which can bring a variability to numerical models. It has been proved that the algorithm is robust, stable, and easy to implement into the SPH framework. With regard to that, the so-called numerical heterogeneity, a concept of parameters variability implementation, is introduced together with examples. The last part of the thesis is dedicated to the application of SPH in real experiments. The first experiment focuses on a high velocity impact. The second experiment deals with an explosion in which the focus is on both the loaded specimen and charge. Since SPH simulates the explosive, detonation products, and the loaded specimen, it is a fully coupled fluid-structure interaction simulation.
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Computational analysis of auxetic structures application potential in impact absorbers
Dohnal, Jakub ; Skalka, Petr (referee) ; Ševeček, Oldřich (advisor)
Master thesis deals with the analysis of the application potential of auxetic materials in the field of shock absorption (absorption of impact energy). Due to their cellular structure and specific geometry, these materials are characterized by a negative Poisson’s ratio, which means that they are able to reduce their transverse dimension under compressive stress in the longitudinal direction. The aim of this work is to use this interesting property for the absorption of kinetic energy. After the introduction, devoted to the theoretical basis and research in the field of auxetic structures, a numerical FEM model is described in detail. The task of the model is to study the mechanical response of auxetic and conventional cellular structure to an impact loading. An explicit solver in the commercial software LS-DYNA is used to numerically simulate fast processes. The results of the analyses are used to compare auxetic and conventional structures and quantify the differences in their ability to dampen the kinetic energy of the impact effectively and gently. It also serves to demonstrate the influence of individual geometric or material parameters on impact attenuation. At the end of the work, numerical simulations are confronted with available experiments in order to verify the informative value of computational models and to point out the application potential of auxetic structures in the discussion. There are also partial recommendations for their design so that they best serve the intended purpose.
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Development and application of computational model of ballistic resistant composite laminate
Urbášek, Jan ; Kubík, Petr (referee) ; Petruška, Jindřich (advisor)
This master thesis is aimed at computational modeling of ballistic resistant layered laminate. The introductory sections of the thesis are aimed at understanding the individual topics that are closely related to the interaction of the projectile and target and computational modeling of this process. The main goal of this thesis was to create a computational model that is able to reflect the behavior of aramid fabric during the interaction with the projectile. During the development of the computational model were used more methods of modeling and also more material models were used. For the purposes of the development of the computational model were used the available data of the companies SVS FEM s.r.o. and VVÚ s.p. The outcome of the diploma thesis is a computational model of aramid fabric which is designed for ballistic protection simulations. This model is validated on the basis of available experiments. The validated computational model is then applied to the simulation of ballistic protection.
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Analysis of welded joints using Finite Element Method
Štěrba, Martin ; Kala, Jiří (referee) ; Hradil, Petr (advisor)
This diploma thesis is concerned with the numerical analysis of welded aluminim structures. In these structures, there are significant decreases in the mechanical properties at the area of the weld and in the heat affected zone as a result of welding. Within this thesis, simulations of quasi-statically loaded welded joints made from EN AW-6082 T6 alloy were performed to investigate the load capacity and ductility of these joints. Computations were performed using a programme system based on an explicit finite element method. To describe material anisotrophy, a nonlinear material model called the Weak texture model was chosen. Material properties of the weld and the heat affected zone were considered to be different from base material. The required material parameters were adopted from available literature, however, material tests and indetification procedure of these parameters were described. In comparison with the experimental data, the results of the numerical simulations showed a relatively good ability of models to capture load capacity of studied welded joints. Nevertheless, due to mesh sensitivity of models caused by localization of deformation, it was not possible to determine ductility of these joints.
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Stress-strain analysis of the thin wall structure subjected to impact load
Tatalák, Adam ; Peč, Michal (referee) ; Návrat, Tomáš (advisor)
This master thesis deals with stress-strain analysis of simplified model of the thin wall transformer case subjected to impact load of electrical blast. Electrical blast is replaced by chemical blast (detonation of high explosive). The problem is solved using computational modeling utilizing the Finite Element Method (FEM) and LS-DYNA solver. After the introduction where detonation and shock wave propagation is explained the analytical approach is presented. This approach serves to results verification. In the next chapter is conducted research of applicable methods from which ALE method is chosen. In preliminary study is performed the mesh size analysis that is focused on finding the size of element which is both computational effective and gives accurate results. Next the infulence of input conditions (shape, location and parametres of high explosive, location of detonation point, boundary conditions) on distribution and time progress of pressure is investigated. Then influence of the opening on upper side of the case on overall pressure redistribution and strain and stress of the case is analysed. The stress-strain analysis of the case´s door which are connected to case by various types of contact models is performed as well as stiffness analysis of these types of contact.
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Parametric study of the absorption element of the rear part of the vehicle
Vražina, Lukáš ; Kubík, Petr (referee) ; Šebek, František (advisor)
In 1995 was published a regulation from RCAR company which determines rules for crash tests in maximum speed of 15 km/h on vehicles lighter than 2,5 ton. The main reason was to reduce costs for car reparation in case of crash in low speed. My diploma thesis is focused on the modifications of deformation part in the car alias absorption part of the vehicle. In the first part of my diploma thesis has been done a research about organisations doing basic car crashes as well as topic focused on nonlinear mechanics and description of explicit FEM. In the second part of my work are settled conditions for crash simulation of a barrier into the car. There is an evaluation of critical force on the stringer. Afterwards the calculating simulation simplified on loading of absorption part and there are some material and form adjustments. In the final part of my diploma thesis is done a result comparison and development of the absorption part.
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