Volume 4, number 2 (2010)
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Item Application of selected multi-axial fatigue criteria on the results of non-proportional fatigue experiments(University of West Bohemia, 2010) Fojtík, František; Fuxa, Jan; Poruba, ZdeněkThe contribution describes the experimental results obtained from the combined loading of the specimens in the field of high-cycle fatigue. Those specimens were manufactured from common construction steel 11523.1, melt T31052. The following experiments were performed: The first set of the specimen was loaded by the alternating bending amplitude. The second set was loaded by the amplitude of the bending in combination with constant inner overpressure. The results were evaluated by the conjugated strength criterion and another generally used multiaxial fatigue criteria. The stress-strain analysis of the specimens by FEM was performed to determine parameters (constants) of particular strength criteria.
Item Vibration analysis of tapered rotating composite beams using the hierarchical finite element(University of West Bohemia, 2010) Ghayour, Rasoul; Ghayour, Mostafa; Ziaei-Rad, SaeedA hierarchical finite element model is presented for the flapwise bending vibration analysis of a tapered rotating multi-layered composite beam. The shear and rotary inertia effects are considered based on the higher shear deformation theory to derive the stiffness and mass matrices of a tapered-twisted rotating and composite beam element. Certain non-composite beams for which comparative results are available in the literature are used to illustrate the application of the proposed technique. Dimensionless parameters are identified from the equations of motion and the combined effects of the dimensionless parameters on the modal characteristics of the rotating composite beams are investigated through numerical studies. The results indicate that, comparedwith the conventional finite element method, the hierarchical finite element has the advantage of using fewer elements to obtain a better accuracy in the calculation of the vibration characteristics of rotating beams such as natural frequencies and mode shapes.Item Validation of the adjusted strength criterion LaRC04 for uni-directional composite under combination of tension and pressure(University of West Bohemia, 2010) Krystek, Jan; Kottner, Radek; Bek, Lukáš; Laš, VladislavStrength of unidirectional composite materials for some combinations of state of stress cannot be successsfully predicted even with modern failure criteria. In case of the combination of compression in the transverse direction and tension in the fiber direction, the criterion LaRC04 was adjusted in previous work. The predicted strengths in this case reach significantly larger values compared to the ultimate strengths of the material in the respective directions. The adjusted criterion is able to predict the failure of unidirectional composite in case of the mentioned combination of loading. The validation of the adjusted criterion is carried out by means of the comparison of experimental results and numerical analysis performed in finite element system MSC.Marc.Item Shape optimization of a Timoshenko beam together with an elastic foundation(University of West Bohemia, 2010) Netuka, Horymír; Machalová, Jitka; Šimeček, RomanIn this article we are going first to aim at the variational formulation of the bending problem for the Timoshenko beam model. Afterwards we will extend this problem to the Timoshenko beam resting on the Winkler foundation, which is firmly connected with the beam. Hereafter a shape optimization for the aforementioned problems is presented. The state problem is here represented by the system of two ordinary differential equations of the second order. The optimization problem is given as a minimization of the so-called compliance functional on the set of all admissible design variables. For our purpose as the design variable we will select the beam thickness. Shape optimization problems have attracted the interest of many applied mathematicians and engineers. The objective of this article is to present a solution method for one of these problems and its demonstration by examples.Item Ductile-brittle behavior at blunted cavities in 3D iron crystals uncovered and covered by copper atoms(University of West Bohemia, 2010) Pelikán, Vladimír; Hora, Petr; Červená, Olga; Spielmannová, Alena; Machová, AnnaThis paper is devoted to studies of the mechanical response of an atomically blunted cavity uncovered and covered by copper atoms by means 3D molecular dynamic (MD) simulations. The cavity is loaded uni-axially in tension mode I. Our question is how the copper atoms influence the ductile-brittle behavior at the crack front of the blunted cavity in comparison with the blunted cavity in pure bcc iron. We show that the dislocation emission is easier in the Fe–Cu system in comparison with pure bcc iron. However, stability of the blunted cavities seems to be weaker in copper region than in pure bcc iron.Item Design of the hydraulic shock absorbers characteristics using relative springs deflections at general excitation of the bus wheels(University of West Bohemia, 2010) Polach, Pavel; Hajžman, MichalThe air-pressure-controlled hydraulic shock absorbers of axles’ air suspension are capable of changing their damping forces in dependence on air pressure in air springs. Due to the possibility of improving dynamic properties of all vehicles that use the axles’ air suspension, BRANO a.s., the Czech producer of shock absorbers, developed semi-active air-pressure-controlled hydraulic telescopic shock absorbers. The force-velocity characteristics of the controlled shock absorbers were designed on the basis of relative deflections of the air springs. As a criterion for the design of the optimum characteristics of the controlled shock absorbers the maximum similarity of dynamic responses of multibody models of the SOR C 12 bus for all the considered weights to the dynamic response of the reference multibody model was chosen. Time histories of relative deflections of the axles’ air springs determined during the simulations are compared. Simulations of running over an obstacle with all the wheels were originally chosen (symmetric kinematic excitation of wheels). Verification of the suitability of the designed force-velocity characteristics of the APCSA described in this paper is performed on the basis of the simulations of general kinematic excitation of wheels. Driving on the artificially created test track according to the Škoda výzkum methodology was chosen.Item Numerical simulation of airflow through the model of oscillating vocal folds(University of West Bohemia, 2010) Prokopová, Jaroslava; Feistauer, Miloslav; Horáček, Jaromír; Kučera, VáclavThis work deals with numerical simulation of flow in time-dependent 2D domains with a special interest in medical applications to airflow in human vocal folds. The mathematical model of this process is described by the compressible Navier-Stokes equations. For the treatment of the time-dependent domain, the Arbitrary Lagrangian- Eulerian (ALE) method is used. The discontinuous Galerkin finite element method (DGFEM) is used for the space semidiscretization of the governing equations in the ALE formulation. The time discretization is carried out with the aid of a linearized semi-implicit method with good stability properties. We present some computational results for flow in a channel with a prescribed periodic motion of a part of the channel walls.Item Numerical approximation of flow in a symmetric channel with vibrating walls(University of West Bohemia, 2010) Sváček, Petr; Horáček, JaromírIn this paper the numerical solution of two dimensional fluid-structure interaction problem is addressed. The fluid motion is modelled by the incompressible unsteady Navier-Stokes equations. The spatial discretization by stabilized finite element method is used. The motion of the computational domain is treated with the aid of Arbitrary Lagrangian Eulerian (ALE) method. The time-space problem is solved with the aid of multigrid method. The method is applied onto a problem of interaction of channel flow with moving walls, which models the air flow in the glottal region of the human vocal tract. The pressure boundary conditions and the effects of the isotropic and anisotropic mesh refinement are discussed. The numerical results are presented.Item Reconstruction of a fracture process zone during tensile failure of quasi-brittle materials(University of West Bohemia, 2010) Veselý, Václav; Frantík, PetrThe paper outlines a technique for estimation of the size and shape of an inelastic zone evolving around a crack tip during the tensile failure of structures/structural members made of quasi-brittle building materials, particularly cementitious composites. The technique is based on an amalgamation of several concepts dealing with the failure of structural materials, i.e. multi-parameter linear elastic fracture mechanics, classical non-linear fracture models for concrete (equivalent elastic crack and cohesive crack models), and the plasticity approach. The benefit of this technique is expected to be seen in the field of the determination of fracture characteristics describing the tensile failure of quasi-brittle silicate-based composites. The method is demonstrated using an example of a (numerically simulated) fracture test involving the three-point bending of a notched beam and validated by experimentally obtained results of three-point bending and wedge-splitting tests taken from the literature.Item Modelling of the mechanical behaviour of porcine carotid artery undergoing inflation-deflation test(University of West Bohemia, 2010) Vychytil, Jan; Moravec, Fanny; Kochová, Petra; Kuncová, Jitka; Švíglerová, JitkaSamples of porcine carotid artery are examined using Tissue bath MAYFLOWER, Perfusion of tubular organs Version, Type 813/6. Pressure-diameter diagrams are obtained for fixed axial extension and volumetric flow rate. Finite element analysis of the experiment, performed using COMSOL software, indicates a negligible effect of given flow rate on the mechanical response of the tested sample. Also the effect of clamped ends is shown to be local only. Hence, static analysis in MATLAB software is performed considering the arterial segment as an incompressible hyperelastic axisymmetric tube. Residual stress at the load-free configuration is taken into account resulting in the overall stiffening of the model. Comparison of theoretical and experimental pressure-diameter curves results in the identification of material parameters using the least square method. In addition to classical hyperelastic models, such as the neo-Hookean and the Fung’s exponential, two-scale model mimicking arrangement of soft tissue is considered.
