In this paper, the harmonic response of the railway vehicle wheelset is investigated by using the... more In this paper, the harmonic response of the railway vehicle wheelset is investigated by using the finite element analysis method. The study relies on the vibrations of a Minden Deutz bogie of a passenger coach, having brake shoes and currently in operation on Romanian railway network. It is well known that by analysing the frequency response it can be identified how the parameters of the wheel-rail system is influencing the level of vibrations and the amount of rolling noise generated. Nonetheless, the approach of determining the harmonic response using the finite element analysis method is the only approach to studying the behaviour of the wheelset at frequencies greater than 1500 Hz.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights a general parameterization procedure of a hexagonal honeycomb is proposed all nine effective elastic properties are obtained analytically by using two new proposed models homogenization of honeycombs enables efficient finite element analyses the numerical results obtained for the effective elastic constants are compared to the ones given by the analytical models
Romanian Journal of Technical Sciences - Applied Mechanics
Homogeneous and isotropic thick spheres loaded with constant internal and/or external pressures c... more Homogeneous and isotropic thick spheres loaded with constant internal and/or external pressures can not be economically designed because the maximum equivalent stress is a local value. It was analytically demonstrated that, by neglecting the body loads, a functionally graded material (FGM) may be characterized in linear static analyses by two material constants: Young's modulus E(r) and Poisson's ratio ν(r). If these two functions are both known, the solution of the problem, displacement and stress distributions may be relatively easy obtained. For the inverse problem, in which a desired stress combination distribution is imposed, finding of E(r) and ν(r) is more difficult, if such a solution exists. More than that, if the solution exists, it is not unique, because two unknown functions are involved. For ν(r) = const., analytical solutions are available for E(r), but only for two particular stress conditions. In this paper, the inverse problem is solved iteratively using a f...
Aeronautical structures are manufactured in a large range of materials like metallic, plastic or ... more Aeronautical structures are manufactured in a large range of materials like metallic, plastic or composite. The maintenance of aerospace structures consists in conventional inspections using different Non-Destructive Evaluation (NDE) methods in order to maximize the structure life and safety. LEISC (Laboratory for Integrity Evaluation of Composite Structures) from the POLITEHNICA University of Bucharest is currently developing NDE methods based on the ultrasonic guided Lamb waves propagation and on the infrared thermography (IRT), methods also adapted for composite and sandwich structures. The present study focuses on the aid provided by the infrared thermography for non-destructive evaluation of aerospace materials and structures. Several samples were manufactured and tested. They consist in different materials employed in aerospace structures (metals, plexiglass, composites, hybrid composites, sandwiches) and include the most commonly encountered kinds of damages (inclusions, loss of material, delaminations, impact damages). Some results concerning the use of the Infrared Thermography (IRT) for monitoring the integrity of different type of materials used in aerospace structures are presented. Both passive and active thermography applications with illustrative examples are considered.
În vederea proiectării/reproiectării aparatului de ochire montat pe o armă automată, trebuie luat... more În vederea proiectării/reproiectării aparatului de ochire montat pe o armă automată, trebuie luate în consideraţie unele probleme legate de comportamentul dinamic sub sarcinile care apar pe timpul tragerii. Este analizată comportarea la vibraţii a structurii mecanice a aparatului de ochire, în conditiile unei excitaţii cu frecvenţa prescrisă de tragere. Studiul este efectuat experimental şi se prezintă o simulare numerică pentru determinarea frecvenţelor proprii ale structurii mecanice a aparatului. Afin de concevoir/reconcevoir l'appareil de visée monté sur une arme automatique, il est à prendre en considération certaines questions liées aux charges dynamiques pendant le tir. Il est analysé le comportement vibratoire de la structure mécanique d'un dispositif de visée, face à une excitation avec la fréquence de tir prescrite. L'étude est effectuée tant par calcul numérique, que expérimentalement, dans des conditions de laboratoire et dans des conditions de fonctionnement...
The paper presents comparatively the measured and estimated natural frequencies and mode shapes o... more The paper presents comparatively the measured and estimated natural frequencies and mode shapes of a rectangular orthotropic panel. The experimental tests were performed using a shaker. The plate was fixed in horizontal position directly on the shaker armature using a rigid rod. The experimental modes shapes were visualized using sand particles. The measured natural frequencies and also the modes shapes correspond to the whole system in motion. So, the analytic model of the plate must include the effect of the vibrator connected to the plates. The purpose of this experimental measurements and analytic modeling of such plates is to further developing a methodology to estimate the material properties of the composite panels. At this research stage, an orthotropic plate with unknown material properties was investigated. Using an adequate finite element model, the mechanical properties of the material were estimated. Using these properties it is possible to numerically estimate the dyna...
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 2018
Sandwich panels with aluminum or glass fiber composite facesheets and polyurethane or polystyrene... more Sandwich panels with aluminum or glass fiber composite facesheets and polyurethane or polystyrene foam core were tested in impact by using an Instron Ceast 9340 impact tower at speeds from 1.5 to 4.5 m/s. The influence of the initial velocity of impact and kinetic energy is analyzed for all types of panels. Particularities of the impact response of the sandwich panels were observed and explained. The facesheet type influence on the damage and penetration of the panels during impact is discussed. If the absorbed energy of the panels is a priority, then the aluminum facesheets and the polystyrene foam core are a good combination. If minimum deformation is required, then composite facesheets and the more rigid polyurethane foam core are a strong option for the sandwich panel design.
IOP Conference Series: Materials Science and Engineering, 2020
A new design of an elastohydrostatic bearing with a structurally elastic pad is theoretically ana... more A new design of an elastohydrostatic bearing with a structurally elastic pad is theoretically analyzed. A single recess circular thrust bearing has the upper pad provided with a large cavity, covered with an elastic metallic membrane. The latter deflects under the pressure distribution in the bearing, creating a radial convergent gap. A simplified axi-symmetric analytical model based on two assumptions is proposed: (i) parabolic approximation for the elastic component of the film thickness and (ii) the maximum elastic deformation of the membrane is calculated analytically using a simplified linear pressure variation in radial direction on the land. Thus, the coupled equations for fluid film and elastic deformation can be solved successively and the bearing performance characteristics can be easily calculated. A parametric analysis, function of a complex elastic parameter and relative recess radius was performed, showing higher load capacity and lower friction similarly to what was p...
IOP Conference Series: Materials Science and Engineering, 2018
The results of the compression test of some specimens made of a chromoplastic polymer show that d... more The results of the compression test of some specimens made of a chromoplastic polymer show that due to the friction between their flat frontal surfaces and the cobalt discs of the test machine to which forces are applied, the state of stress in the specimens is no longer uniaxial and homogeneous, the deformations along their axis being uneven. Experimental research and numerical analysis using finite element method confirms this appreciation and the differences that occur as regards the state of tension over the situation where friction is absent.
IOP Conference Series: Materials Science and Engineering, 2016
The flat plates, perforated by a large number of holes are widely used in the engineering, especi... more The flat plates, perforated by a large number of holes are widely used in the engineering, especially in the component of the process equipment. Strength calculations and experimental methods used in the actual literature for study perforated plates, do not present the problem in all its complexity for stress distribution and displacements. Research and doctoral theses in last decades, with methods characteristic of the respective periods were engaged either perforated plates considered infinite and requested the median plane or rarely, plate loaded normal to the median plane, with a small number of holes. In this work the stress distribution and displacement is presented for a circular plate perforated by 96 holes arranged in a grid of squares, simply supported on the outline and loaded through a central concentrated force or by uniformly distributed load. It conducted a numerical analysis by finite element method (FEM) with a proper meshing of the plate and an experimental study by holographic interferometry. Holographic interferometry method permits to measure, with high accuracy, extremely small displacements and comparing the results with those obtained by FEM becomes sustainable. Supplementary, an analysis of a non-perforated plate with the same dimensions and stiffness, similar loaded, was performed, determining the coefficient of stress concentration for a particular arrangement of holes.
A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both th... more A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both the coupled structural-electric behavior of the switch as well as its RF behavior. The device with distributed parameters is subject to several analyses from which the parameters of the macromodel are extracted, by model reduction. From the coupled structural-electrostatic analysis the parametric capacitance and the effective stiffness coefficients of the switch are extracted. From the RF characteristics in the up stable state, the transmission line parameters are extracted. Finally, all parameters are combined in a Spice circuit model, which is controlled by the MEMS actuation voltage and is excited with the RF signal. The procedure is applied to a capacitive switch. Relative modeling errors with respect to the non-reduced model, considered as reference, of less than 3 % for the RF characteristics and less than 1 % for the mechanical characteristics are obtained.
In this paper, the harmonic response of the railway vehicle wheelset is investigated by using the... more In this paper, the harmonic response of the railway vehicle wheelset is investigated by using the finite element analysis method. The study relies on the vibrations of a Minden Deutz bogie of a passenger coach, having brake shoes and currently in operation on Romanian railway network. It is well known that by analysing the frequency response it can be identified how the parameters of the wheel-rail system is influencing the level of vibrations and the amount of rolling noise generated. Nonetheless, the approach of determining the harmonic response using the finite element analysis method is the only approach to studying the behaviour of the wheelset at frequencies greater than 1500 Hz.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights a general parameterization procedure of a hexagonal honeycomb is proposed all nine effective elastic properties are obtained analytically by using two new proposed models homogenization of honeycombs enables efficient finite element analyses the numerical results obtained for the effective elastic constants are compared to the ones given by the analytical models
Romanian Journal of Technical Sciences - Applied Mechanics
Homogeneous and isotropic thick spheres loaded with constant internal and/or external pressures c... more Homogeneous and isotropic thick spheres loaded with constant internal and/or external pressures can not be economically designed because the maximum equivalent stress is a local value. It was analytically demonstrated that, by neglecting the body loads, a functionally graded material (FGM) may be characterized in linear static analyses by two material constants: Young's modulus E(r) and Poisson's ratio ν(r). If these two functions are both known, the solution of the problem, displacement and stress distributions may be relatively easy obtained. For the inverse problem, in which a desired stress combination distribution is imposed, finding of E(r) and ν(r) is more difficult, if such a solution exists. More than that, if the solution exists, it is not unique, because two unknown functions are involved. For ν(r) = const., analytical solutions are available for E(r), but only for two particular stress conditions. In this paper, the inverse problem is solved iteratively using a f...
Aeronautical structures are manufactured in a large range of materials like metallic, plastic or ... more Aeronautical structures are manufactured in a large range of materials like metallic, plastic or composite. The maintenance of aerospace structures consists in conventional inspections using different Non-Destructive Evaluation (NDE) methods in order to maximize the structure life and safety. LEISC (Laboratory for Integrity Evaluation of Composite Structures) from the POLITEHNICA University of Bucharest is currently developing NDE methods based on the ultrasonic guided Lamb waves propagation and on the infrared thermography (IRT), methods also adapted for composite and sandwich structures. The present study focuses on the aid provided by the infrared thermography for non-destructive evaluation of aerospace materials and structures. Several samples were manufactured and tested. They consist in different materials employed in aerospace structures (metals, plexiglass, composites, hybrid composites, sandwiches) and include the most commonly encountered kinds of damages (inclusions, loss of material, delaminations, impact damages). Some results concerning the use of the Infrared Thermography (IRT) for monitoring the integrity of different type of materials used in aerospace structures are presented. Both passive and active thermography applications with illustrative examples are considered.
În vederea proiectării/reproiectării aparatului de ochire montat pe o armă automată, trebuie luat... more În vederea proiectării/reproiectării aparatului de ochire montat pe o armă automată, trebuie luate în consideraţie unele probleme legate de comportamentul dinamic sub sarcinile care apar pe timpul tragerii. Este analizată comportarea la vibraţii a structurii mecanice a aparatului de ochire, în conditiile unei excitaţii cu frecvenţa prescrisă de tragere. Studiul este efectuat experimental şi se prezintă o simulare numerică pentru determinarea frecvenţelor proprii ale structurii mecanice a aparatului. Afin de concevoir/reconcevoir l'appareil de visée monté sur une arme automatique, il est à prendre en considération certaines questions liées aux charges dynamiques pendant le tir. Il est analysé le comportement vibratoire de la structure mécanique d'un dispositif de visée, face à une excitation avec la fréquence de tir prescrite. L'étude est effectuée tant par calcul numérique, que expérimentalement, dans des conditions de laboratoire et dans des conditions de fonctionnement...
The paper presents comparatively the measured and estimated natural frequencies and mode shapes o... more The paper presents comparatively the measured and estimated natural frequencies and mode shapes of a rectangular orthotropic panel. The experimental tests were performed using a shaker. The plate was fixed in horizontal position directly on the shaker armature using a rigid rod. The experimental modes shapes were visualized using sand particles. The measured natural frequencies and also the modes shapes correspond to the whole system in motion. So, the analytic model of the plate must include the effect of the vibrator connected to the plates. The purpose of this experimental measurements and analytic modeling of such plates is to further developing a methodology to estimate the material properties of the composite panels. At this research stage, an orthotropic plate with unknown material properties was investigated. Using an adequate finite element model, the mechanical properties of the material were estimated. Using these properties it is possible to numerically estimate the dyna...
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 2018
Sandwich panels with aluminum or glass fiber composite facesheets and polyurethane or polystyrene... more Sandwich panels with aluminum or glass fiber composite facesheets and polyurethane or polystyrene foam core were tested in impact by using an Instron Ceast 9340 impact tower at speeds from 1.5 to 4.5 m/s. The influence of the initial velocity of impact and kinetic energy is analyzed for all types of panels. Particularities of the impact response of the sandwich panels were observed and explained. The facesheet type influence on the damage and penetration of the panels during impact is discussed. If the absorbed energy of the panels is a priority, then the aluminum facesheets and the polystyrene foam core are a good combination. If minimum deformation is required, then composite facesheets and the more rigid polyurethane foam core are a strong option for the sandwich panel design.
IOP Conference Series: Materials Science and Engineering, 2020
A new design of an elastohydrostatic bearing with a structurally elastic pad is theoretically ana... more A new design of an elastohydrostatic bearing with a structurally elastic pad is theoretically analyzed. A single recess circular thrust bearing has the upper pad provided with a large cavity, covered with an elastic metallic membrane. The latter deflects under the pressure distribution in the bearing, creating a radial convergent gap. A simplified axi-symmetric analytical model based on two assumptions is proposed: (i) parabolic approximation for the elastic component of the film thickness and (ii) the maximum elastic deformation of the membrane is calculated analytically using a simplified linear pressure variation in radial direction on the land. Thus, the coupled equations for fluid film and elastic deformation can be solved successively and the bearing performance characteristics can be easily calculated. A parametric analysis, function of a complex elastic parameter and relative recess radius was performed, showing higher load capacity and lower friction similarly to what was p...
IOP Conference Series: Materials Science and Engineering, 2018
The results of the compression test of some specimens made of a chromoplastic polymer show that d... more The results of the compression test of some specimens made of a chromoplastic polymer show that due to the friction between their flat frontal surfaces and the cobalt discs of the test machine to which forces are applied, the state of stress in the specimens is no longer uniaxial and homogeneous, the deformations along their axis being uneven. Experimental research and numerical analysis using finite element method confirms this appreciation and the differences that occur as regards the state of tension over the situation where friction is absent.
IOP Conference Series: Materials Science and Engineering, 2016
The flat plates, perforated by a large number of holes are widely used in the engineering, especi... more The flat plates, perforated by a large number of holes are widely used in the engineering, especially in the component of the process equipment. Strength calculations and experimental methods used in the actual literature for study perforated plates, do not present the problem in all its complexity for stress distribution and displacements. Research and doctoral theses in last decades, with methods characteristic of the respective periods were engaged either perforated plates considered infinite and requested the median plane or rarely, plate loaded normal to the median plane, with a small number of holes. In this work the stress distribution and displacement is presented for a circular plate perforated by 96 holes arranged in a grid of squares, simply supported on the outline and loaded through a central concentrated force or by uniformly distributed load. It conducted a numerical analysis by finite element method (FEM) with a proper meshing of the plate and an experimental study by holographic interferometry. Holographic interferometry method permits to measure, with high accuracy, extremely small displacements and comparing the results with those obtained by FEM becomes sustainable. Supplementary, an analysis of a non-perforated plate with the same dimensions and stiffness, similar loaded, was performed, determining the coefficient of stress concentration for a particular arrangement of holes.
A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both th... more A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both the coupled structural-electric behavior of the switch as well as its RF behavior. The device with distributed parameters is subject to several analyses from which the parameters of the macromodel are extracted, by model reduction. From the coupled structural-electrostatic analysis the parametric capacitance and the effective stiffness coefficients of the switch are extracted. From the RF characteristics in the up stable state, the transmission line parameters are extracted. Finally, all parameters are combined in a Spice circuit model, which is controlled by the MEMS actuation voltage and is excited with the RF signal. The procedure is applied to a capacitive switch. Relative modeling errors with respect to the non-reduced model, considered as reference, of less than 3 % for the RF characteristics and less than 1 % for the mechanical characteristics are obtained.
Uploads
Papers by stefan sorohan