Volume 2, number 1 (2008)
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Item An influence of static load on fatigue life of parts under combined stress(University of West Bohemia, 2008) Balda, Miroslav; Svoboda, JaroslavThe paper deals with a special case of multiaxial fatigue in a plain stress possessing one component static and the other dynamic. Exponents of Haigs’ limit curves were obtained experimentally both for tensile fatigue test and combined tensile/torgue tests. Errors of estimated fatigue lives are less than 20 %.
Item Analysis of the conical piezoelectric acoustic emission transducer(University of West Bohemia, 2008) Červená, Olga; Hora, PetrAnalyses of the properties of conical piezoelectric acoustic emission transducer are presented here. The conical piezoelectric transducer is used to scanning normal displacement on a surface of testing constructions in NDT methods, such as acoustic emission. The simplified one-dimensional analysis based on the equivalent circuit of conical waveguide is recapitulated. FEM analysis on this transducer is presented. Both the frequency response characteristic of the transducer and his time response on pulse excitation are results of this analysis. All of computations are done for various cone angles of piezoceramic (PTZ-H5) element and various sizes of the cylindrical backing of the sensor.Item A sandwich bar element for geometric nonlinear thermo-elastic analysis(University of West Bohemia, 2008) Ďuriš, Rastislav; Murín, JustínThis contribution deals with a two-node straight sandwich composite bar element with constant double symmetric rectangular cross-sectional area. This new bar element (based on the non-linear second-order theory) is intended to perform the non-incremental full geometric non-linear analysis. Stiffness matrix of this composite bar contains transfer constants, which accurately describe polynomial uniaxial variation of the material thermo-physical properties. In the numerical experiments the weak coupled thermo-structural geometric non-linear problem was solved. Obtained results were compared with several analyses made by ANSYS programme. Findings show good accuracy of this new finite element. The results obtained with this element do not depend on the element mesh density.Item Examination of the fatigue life under combined loading of specimens(University of West Bohemia, 2008) Fojtík, František; Fuxa, JanThis contribution describes experimental results under combined loading of specimens manufactured from common construction steel 11523. Specimens were gradually loaded by amplitude of the torque, then by combination of torque and tension prestress. The last set of specimens was loaded in combination of torque and inner over-pressure. To obtain the required input values the stress-strain analysis of specimens by finite element method in software Ansys was performed within the last experiment. For evaluation of the results the Fuxa’s criterion was applied. The performed experiments and their results embody a good agreement with bellow mentioned conjugated strength criterion. The experiments were performed on reconstructed testing machine equipped by pressure chamber.Item Optimization of tram face with respect to passive safety(University of West Bohemia, 2008) Hynčík, Luděk; Kocková, Hana; Číhalová, Lenka; Cimrman, RobertAn impact of a pedestrian and a tram or even an impact of two trams is a common traffic accident in towns. Hence there is an effort to develop such traffic means that minimize injuries of victims. The article deals with the optimization of placement of a previously proposed tram fender to decrease pedestrian injury risk. Further the influence of the tram fender made from different materials on passengers and tram driver injuries is investigated. The pedestrian, driver and passengers aremodeled by a rigid body human model. The results analysis uses standard injury criteria based on body parts accelerations.Item Fatigue crack shape prediction based on vertex singularity(University of West Bohemia, 2008) Hutař, Pavel; Náhlík, LubošDue to the existence of vertex singularity at the point where the crack intersects the free surface, stress distribution around the crack tip and the type of the singularity is changed. In the interior of the specimen the classical singular behaviour of the crack is dominant and can be described using analytic equations. Contrary to this, at the free surface or in the boundary layer close to free surface the vertex singularity is significant. The influence of vertex singularity on crack behaviour and a crack shape for a three-dimensional structure is described in this paper. The results presented make it possible to estimate fatigue crack growth rate and crack shape using the concept of the generalized stress intensity factor. The estimated fatigue crack shape can help to provide a more reliable estimation of the fatigue life of the structures considered.Item Influence of elasticity parameters and direction of material axes on velocity of R-waves in thin composite panel(University of West Bohemia, 2008) Kroupa, Tomáš; Červ, JanThe present paper deals with the low cycle fatigue analysis of the low pressure (LP) steam turbine blade. The blade is cyclically loaded by the centrifugal force because of the repeated startups of the turbine. The goal of the research is to develop a technique to assess fatigue life of the blade and to determine the number of startups to the crack initiation. Two approaches were employed. First approach is based on the elastic finite element analysis. Fictive ‘elastic’ results are recalculated using Neuber’s rule and the equivalent energy method. Triaxial state of stress is reduced using von Mises theory. Strain amplitude is calculated employing the cyclic deformation curve. Second approach is based on elastic-plastic FE analysis. Strain amplitude is determined directly from the FE analysis by reducing the triaxial state of strain. Fatigue life was assessed using uniaxial damage parameters. Both approaches are compared and their applicability is discussed. Factors that can influence the fatigue life are introduced. Experimental low cycle fatigue testing is shortly described.Item Low cycle fatigue analysis of a last stage steam turbine blade(University of West Bohemia, 2008) Měšťánek, PetrThe present paper deals with the low cycle fatigue analysis of the low pressure (LP) steam turbine blade. The blade is cyclically loaded by the centrifugal force because of the repeated startups of the turbine. The goal of the research is to develop a technique to assess fatigue life of the blade and to determine the number of startups to the crack initiation. Two approaches were employed. First approach is based on the elastic finite element analysis. Fictive ‘elastic’ results are recalculated using Neuber’s rule and the equivalent energy method. Triaxial state of stress is reduced using von Mises theory. Strain amplitude is calculated employing the cyclic deformation curve. Second approach is based on elastic-plastic FE analysis. Strain amplitude is determined directly from the FE analysis by reducing the triaxial state of strain. Fatigue life was assessed using uniaxial damage parameters. Both approaches are compared and their applicability is discussed. Factors that can influence the fatigue life are introduced. Experimental low cycle fatigue testing is shortly described.Item Stress analysis of the O-element pipe during the process of flue gases purification(University of West Bohemia, 2008) Nekvasil, RichardEquipment for flue gases purification from undesired substances is used throughout power and other types of industry. This paper deals with damaging of the O-element pipe designed to remove sulphur from the flue gases, i.e. damaging of the pipe during flue gases purification. This purification is conducted by spraying the water into the O-shaped pipe where the flue gases flow. Thus the sulphur binds itself onto the water and gets removed from the flue gas. Injection of cold water into hot flue gases, however, causes high stress on the inside of the pipe, which can gradually damage the O-element pipe. In this paper initial injection of water into hot pipe all the way to stabilization of temperature fields will be analyzed and the most dangerous places which shall be considered for fatigue will be determined.Item Application of the simulation based reliability analysis on the LBB methodology(University of West Bohemia, 2008) Svrček, Miroslav; Pečínka, LadislavGuidelines on how to demonstrate the existence of Leak Before Break (LBB) have been developed in many western countries. These guidelines, partly based on NUREG/CR-6765, define the steps that should be fulfilled to get a conservative assessment of LBB acceptability. As a complement and also to help identify the key parameters that influence the resulting leakage and failure probabilities, the application of Simulation Based Reliability Analysis is under development. The used methodology will be demonstrated on the assessment of through wall leakage crack stability according R6 method. R6 is a known engineering assessment procedure for the evaluation of the integrity of the flawed structure. Influence of thermal ageing and seismic event has been elaborate.Item Multibody simulations of trolleybus vertical dynamics and influences of spring-damper structural elements(University of West Bohemia, 2008) Polach, Pavel; Hajžman, MichalVertical dynamic properties of the ˇSKODA 21 Tr low-floor trolleybus were investigated on an artificial test track when driving with a real vehicle and when simulating driving with a multibody model along a virtual test track. Driving along the artificial test track was aimed to determine vertical dynamic properties of the real trolleybus and on the basis of them to verify computer trolleybus models. Time histories and extreme values of the air springs relative deflections are the monitored quantities. Due to differences of the experiments and the computer simulations results the influences of the characteristics of the spring-damper structural elements of the axles suspension and the radial characteristics of the tires used in the trolleybus multibody model on the extreme values of the monitored quantities are evaluated.Item Contribution to stress sensitivity analysis of the shell finite elements(University of West Bohemia, 2008) Sága, Milan; Vaško, Milan; Jandačka, Jozef; Hoľková, ZuzanaThe sensitivity analysis and the finite elements method represent an important tool for the influence analysis of the structural parameters. This analysis plays a significant role in the decision process of the formulation of the structural optimizing or probability analysis. The goal of the paper is to present theoretic and numerical aspects of the shell element stress sensitivity analysis with the respect to the thickness and its implementation into finite element code MATFEM inbuilt to Matlab.Item The influence of the shape of a saw-cut notch in quasi-brittle 3PB specimens on the critical applied force(University of West Bohemia, 2008) Seitl, Stanislav; Řoutil, Ladislav; Klusák, Jan; Veselý, VáclavValues of fracture parameters of quasi-brittle building materials are usually determined from results of tests performed on notched testing specimens. The contribution deals with the influence of various shapes of tips of notches prepared by a diamond saw in three point bending (3PB) specimens. The influence of the notch tip shape on the applied force corresponding to a failure initiation at the notch tip and also on the critical applied force appropriate to the maximal load-bearing capacity of the specimen is studied. Calculations are performed in two finite element method (FEM) systems (ATENA, ANSYS) based on two different approaches to fracture description (Cohesive crack models and LEFM, respectively). The numerical results obtained by both FEM systems are compared. The influence of notch shapes and width is quantified.Item Numerical approximation of fluid-structure interaction problems(University of West Bohemia, 2008) Sváček, PetrThis paper is devoted to numerical approximations of fluid-structure interaction problems. Namely the problem of interaction of turbulent flow over flexibly supported airfoil is addressed. In order to model the turbulence effects the flow is described by Reynolds Averaged Navier-Stokes (RANS) equations. The Reynolds equations and the turbulence model is numerically approximated by the finite element method. In order to avoid spurious oscillations stabilization procedures are applied. The application of the developed numerical method is shown in several numerical experiments.Item Orientation, anisotropy, clustering, and volume fraction of smooth muscle cells within the wall of porcine abdominal aorta(University of West Bohemia, 2008) Tonar, Zbyněk; Kochová, Petra; Janáček, JiříWe analyzed tissue samples of the normal porcine abdominal aorta using stereological assessment of histological sections through the tunica media layer. The results demonstrated that the local volume fraction of smooth muscle cells within tunica media does not differ among samples taken round the circumference of the artery, and that volume fraction can be assessed in sections stained with green trichrome as well as with immunohistochemistry against actin. The distribution of angles between the long axes of nuclei of the smooth muscle cells and the radial direction was different from normal. The profiles of smooth muscle cells were distributed in an isotropic, but an inhomogeneous manner.Item Comparison study of the computational methods for eigenvalues IFE analysis(University of West Bohemia, 2008) Vaško, Milan; Sága, Milan; Handrik, MariánThe goal of the paper is to present a non-traditional computational tool for structural analysis with uncertainties in material, geometric and load parameters. Uncertainties are introduced as bounded possible values— intervals. The main objective has been to propose algorithms for interval modal and spectral computations on FEM models suggested by authors and their comparison with Monte Carlo.Item Two-scale hyperelastic model of a material with prestress at cellular level(University of West Bohemia, 2008) Vychytil, Jan; Holeček, MiroslavWe propose the two-scale hyperelastic model of a material defined at micro-scale. The microstructure, motivated by the arrangement of soft tissues at the cellular level, is formed by an incompressible inclusion and linear elastic elements. The prestress of such structure is maintained by the assumption of constant volume of the inclusion. In the continuum limit, the prestressed microstructure is considered as a single material particle governed by the macroscopic deformation gradient. Thus the strain-energy is obtained as a function of both macro-deformation and micro-prestress. Although we have no analytical formula, an approximation is found using assumptions that hold for soft tissues. It shows clearly the ability of the model to control the overall mechanical behaviour by setting the prestress at micro-scale (the prestress-induced stiffening).Item A computational investigation of vibration of stationary and rotating structures submerged in a liquid(University of West Bohemia, 2008) Zapomněl, Jaroslav; Čermák, Libor; Pochylý, FrantišekTo realize some technological processes components of a number of stationary and rotating machines work submerged in various liquids. Therefore their vibration is significantly influenced by their interaction with the medium in the surrounding space. An important tool for investigation of their behavior is a computer modelling method. In the computational models it is assumed that the vessel and the submerged bodies are absolutely rigid, the liquid is perfect and incompressible, amplitude of the vibration is small, and the flow and the oscillations are 2D. On these assumptions the pressure distribution in the liquid is described by a Laplace equation. For its solution a finite element or a finite difference methods can be used. The region filled with the liquid is, in general, of irregular shape. To describe its geometry or to perform its discretization the B´ezier surfaces can be utilized. In the cases when the region filled with the liquid changes its boundaries there is a possibility to transform solution of the governing equation from the primary region into the unit square domain making use of the dimensionless coordinates. The advantage is that this approach does not require to change the discretization even if the primary region changes its shape. On the other hand the form of the transformed equation is more complicated than the form of the original one.Item Usage of modal synthesis method with condensation in rotor dynamics(University of West Bohemia, 2008) Zeman, Vladimír; Šašek, JakubThe paper deals with mathematical modelling of vibration and modal analysis of rotors composed of a flexible shaft and several flexible disks. The shaft is modelled as a one dimensional continuum whereon flexible disks modelled as a three dimensional continuum are rigid mounted to shaft. The presented approach allows to introduce continuously distributed centrifugal and gyroscopic effects. The finite element method was used for shaft and disks discretization. The modelling of such flexible multi-body rotors with large DOF number is based on the system decomposition into subsystems and on the modal synthesis method with condensation. Lower vibration mode shapes of the mutually uncoupled and non-rotating subsystems are used for creation of the rotor condensed mathematical model. An influence of the different level of a rotor condensationmodel on the accuracy of calculated eigenfrequencies and eigenvectors is discussed.Item Identification of material properties of sandwich structure with piezoelectric patches(University of West Bohemia, 2008) Zemčík, Robert; Sadílek, PetrThe work focuses on light-weight sandwich structures made of carbon-epoxy skins and foam core which have unique bending stiffness compared to conventional materials. The skins are manufactured by vacuum autoclave technology from unidirectional prepregs and the sandwich is then glued together. The resulting material properties of the structure usually differ from those provided by manufacturer or even those obtained from experimental tests on separatematerials, which makes computationalmodels unreliable. Therefore, the properties are identified using the combination of experimental analysis of the sandwich with attached piezoelectric transducer and corresponding static and modal finite element analyses. Simple mathematical optimization with repetitive finite element solution is used. The model is then verified by transient analysis when the piezoelectric patch is excited by harmonic signals covering the first two eigen-frequencies and the induced oscillations are measured by laser sensor.
