Papers by Keyword: FEM Model

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Authors: Jan Ondráček, Aleš Materna, Vladislav Oliva
Abstract: A 2D elastic-plastic FEM simulation of growing fatigue crack under combined mode I and II loading was performed. An inclined fatigue crack propagated in a sheet of an Al-alloy D16CT1. The effect of increasing mode-mixity on cyclic zone size, shape and the amount of dissipated energy was investigated.
Authors: Tiberiu Axinte
Abstract: The paper presents the effect of the discontinuity of the rails of a ferry boat and the presence of lower modulus insulation material at the gap to the variations of stresses in the insulated rail. The analysis consists of a three-dimensional wheel rail contact model based on the finite element method. One of the results shows that the maximum stress occurs in the subsurface of the railhead of the ferry boat. The ratio of the elastic modulus of the railhead and insulation material is found to alter the levels of stress concentration. Numerical result indicates that a higher elastic modulus insulating material can reduce the stress concentration in the railhead but will generate higher stresses in the insulation material, leading to earlier failure of the insulation material. A general subsurface crack propagation analysis methodology is used for the wheel and rail rolling contact. The fatigue damage in the wheel is calculated using a previously developed mixed-mode fatigue crack propagation model. The advantages of the proposed methodology are that it can accurately represent the contact stress of complex mechanical components and can consider the effect of loading non-proportionality. The effects of wheel diameter, vertical loading amplitude, initial crack size, location and orientation on stress intensity factor range are investigated using the proposed model. The prediction results of the proposed methodology are compared with in field observations. The contact elements were used to stimulate the interaction between a wheel and a railhead. Variations in contact stress fields at various locations of the rail are sensitive to the contact distance. The location of the maximum von Mises stress was shifted to the contact surface as the contact point moves close to the rail end. A higher stress, larger deflection and significant plastic deformation occurring at the rail from ferry boat may lead to deterioration at the rail end.
Authors: Aleš Lufinka, Michal Petrů
Abstract: Substitute of the traditional materials with new plastic-based and composite materials is a trend in today's automotive industry. Mechanical properties of the composite parts are highly influenced by the composite production (material of fibers and their distribution, type and density of a filler). Knowledge of the specific composite material mechanical properties is necessary for CAD modeling and FEM calculations during the assembly design. These mechanical properties can be obtained by creating a composite structure in FEM software. However, the real composite may be different from the ideal FEM model (due to inaccuracies in its manufacture). Therefore, it is highly advisable to verify the modeling results by measuring of the real composite material properties. Identification and verification of the composite tube mechanical properties used in the hybrid car tailgate are described in this paper.
Authors: Ekaterina Astafyeva
Abstract: Soft soils are well represented as the foundation of buildings all over the world. Settlements of buildings that are built on soft soils are developing over decades and often uneven. This can cause structural damages to constructions and as consequence unplanned repairs or even collapses of buildings in general. To justify the use of different models of soil mechanics it is necessary to carry out their verification. Verification of the model consists of compliance to the simple laboratory experiments and of the adequacy of the field tests description. And the most important thing is that the results of calculations should be based on comparison between series of field observations. The principal difficulty of comparing calculation results with field observations is that the actual soil deformation is developing over a long time, and most of the calculation methods are aimed to obtain finite values of deformations. Comparison between data of finite deformations and data of field observations is not quite correct, because, as a rule, in-situ (field) observations recorded incomplete development process of deformations but not only the final result of settlement. Therefore, to compare these calculations and observations we should select calculation models that can examine the development of deformations in time. Based on the above, it is interesting to analyze the applicability of the most common engineering methods and calculation models of the soils that underlie different calculation programs used in practice.
Authors: Peng Wang, Hai Bo Chen, Wei Dong Huang, Yue Lin, Hui Wu Zhang
Abstract: Bolted connection technology has been widely used in steel structure engineering. Conventional structural analysis softwares solve related problems with the assumption of regarding the bolted connection as a rigid joint connection. Thus the calculated internal forces of the structure members are bigger than those of real measurements, and the calculated displacement are smaller than the experimental ones under the same load. One of the main reasons is the bolt slippage. In the lattice structure, there are a large number of bolted connections with thin connection members and small-diameter bolts, however, their clamping forces are relatively small. These characteristics have significant effects on the static response of the lattice structure. In this paper, in comparison with the test results, the deformation-load curves of the bolt connections are introduced into the finite element simulation, revealing the effect of bolt slippage on the static response of lattice structure. The simulation and test results show that the bolt slippage causes the redistribution of the member internal forces of the lattice structure and increases the displacement of the lattice structure,thus the simulation results with bolt slippage are more close to the real values. The proposed algorithm and simulation results would provid good reference for further engineering applications.
Authors: Pavel Klapálek, Lenka Melzerová
Abstract: This article will examine the effect of the knots distribution on strength of glued laminated timber beams. A finite element model was made to simulate glued laminated timber beams with defects (knots) to simulate and predict behavior in areas containing knots while bending. This model was then compared with results from static bending test of glued laminated timber beam. The initial position of the rupture was then compared with FEM model [6], so the influence of knots on strength could be determined.
Authors: Aleš Materna, Vladislav Oliva
Abstract: A 3D elastic-plastic FEM model for prediction of planar fatigue crack growth is presented. The model is based on the concept of local low-cycle fatigue of a small material volume in front of a high cycle crack. A local crack front advance is modelled by the successive release of finite element mesh nodes in the plane of propagation. The release of the nodes is controlled by the value of the Smith-Watson-Topper fatigue damage parameter in the surrounding elements. The effect of the single tensile overload on the fatigue crack growth and on the fatigue crack front shape is modelled.
Authors: Gianluca Buffa, Livan Fratini, Fabrizio Micari, Giuseppe Previte
Abstract: Solid state bonding recurs in several manufacturing processes, as extrusion of hollow profiles and solid welding processes. Among the latter, Friction Stir Welding (FSW) is nowadays of particular industrial interest because of the specific advantages with respect to the classic welding technologies. Proper conditions of pressure, temperature, strain and strain rate are needed in order to get the final effective bonding. In the paper the authors compare different solid state bonding conditions obtained at the varying of the main process parameters in FSW of butt joints of AA5754 aluminum alloys. The experimental results are compared with the numerical ones from a FEM model previously developed by the authors, in order to investigate an effective bonding criterion to be implemented into the FSW numerical model.
Authors: Filip Tikal, Michal Duchek, Jan Nacházel
Abstract: The purpose of this study was to identify possible causes of longitudinal surface cracks found during early stages of ingot breakdown. However, these cracks need not necessarily form during forging or as a result of poor quality of the surface in metallurgical terms. Under certain conditions, they may occur even as the ingot is being heated in the furnace to the forging temperature. The cracks probably form within a few minutes after placing the ingot in the furnace as a result of the temperature gradient, which is most severe on the ingot surface. A numerical model was created to represent the case of three ingots in a furnace. Upon casting, the ingots are cooled down to no more than 600°C and then placed in a furnace at 1,100 - 1,200°C. Numerical simulations were used to analyse their internal stresses and temperatures.
Authors: Josef Vosáhlo, Ondřej Novák, Michal Petrů, Petr Lepšík
Abstract: This article deals with a study and optimization of technology for a production of low-diameter biodegradable vascular grafts using modified electrospinning device. This production method allows preparation of grafts with diameter under 6 mm, which serve as carriers of tissue cells. Also their production and establishing of a simulation model, which describes their behaviour under internal pressure. For this purpose spinning device was created with a rotary collector, which allows obtaining the desired fiber orientation that is perpendicular to the axis of rotation. This orientation is necessary for the efficient proliferation of cells and future mechanical properties of artificial blood vessels. Formations created in this way were subjected to mechanical testing. Based on obtained data a suitable material model and FEM model of artificial vessels was established. These vessels were loaded with internal pressure corresponding with standard blood pressure in human body (120/80 mmHg). The results allow assessing the behaviour of the blood vessels during cultivation and proliferation of the cells in bioreactor. This is very important, because in bioreactor a medium, which pulsed under some pressure, is applied. Based on the obtained results were recommended optimization of production process, which led to suitable vessel properties.
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