Showing papers on "Loss factor published in 2011"

Loss determination methodology for a piezoelectric ceramic: new phenomenological theory and experimental proposals

Abstract: The key factor to the miniaturization of piezoelectric devices is power density, which is limited by the heat generation or loss mechanisms. There are three loss components in general in piezoelectric vibrators/resonators, i.e., dielectric, elastic and piezoelectric losses. The mechanical quality factor, determined by these three factors, is the Figure Of Merit (FOM) in the sense of loss or heat generation. In this paper, we introduce a new loss phenomenology and innovative measuring methods based on the theory. First, quality factors at resonance and antiresonance for the k31, k33, kt and k15 vibration modes are derived theoretically, and the methodology for determining loss factors in various orientations (i.e., loss anisotropy) is provided. For simplicity, we focus on materials with ∞ mm (equivalent to 6 mm) crystal symmetry for deriving the loss factors of a polycrystalline ceramic, and 14 different loss factors among 20 in total can be obtained from the measurements. Second, we propose the experimental methods for measuring both mechanical quality factors QA and QB at the resonance and antiresonance modes: a continuous admittance/impedance spectrum measuring method (traditional with temperature rise) and a burst mode (to circumvent the temperature effect).

Identification of Structural Stiffness and Energy Dissipation Parameters in a Second Generation Foil Bearing: Effect of Shaft Temperature

Abstract: Established high temperature operation of gas foil bearings (GFB) is of great interest for gas turbine applications. The effects of (high) shaft temperature on the structural stiffness and mechanical energy dissipation parameters of a foil bearing (FB) must be assessed experimentally. Presently, a hollow shaft warmed by an electric heater holds a floating second generation FB that is loaded dynamically by an electromagnetic shaker. In tests with the shaft temperature up to 184°C, the measurements of dynamic load and ensuing FB deflection render the bearing structural parameters, stiffness and damping, as a function of excitation frequency and amplitude of motion. The identified FB stiffness and viscous damping coefficients increase with shaft temperature due to an increase in the FB assembly interference or preload. The bearing material structural loss factor best representing mechanical energy dissipation decreases slightly with shaft temperature while increasing with excitation frequency. Separate static load measurements on the bearing also make evident the preload of the test bearing-shaft system at room temperature. The loss factor obtained from the area inside the hysteresis loop of the static load versus the deflection curve agrees remarkably with the loss factor obtained from the dynamic load measurements. The static procedure offers substantial savings in cost and time to determine the energy dissipation characteristics of foil bearings. Post-test inspection of the FB reveals sustained wear at the locations, where the bumps contact the top foil and the bearing sleeve inner surface, thus, evidences the bearing energy dissipation by dry friction.

Effects of PZT particle-enhanced ply interfaces on the vibration damping behavior of CFRP composites

Abstract: In this study, vibration damping behavior of carbon fiber reinforced polymer composites was investigated when ply interfaces were enhanced by lead zirconate titanate (PZT) particles. The influence of particle loading and carbon black coating of particles was analyzed using the dynamic mechanical analysis. When plain PZT particles were distributed in the ply interfaces, the loss factor increased but suddenly dropped with increased particle loading, producing a threshold effect. As the loss factor represents the joule heat of electric current between PZT particles and carbon fibers, the sudden drop implies that there exists incomplete connectivity. To demonstrate the effect of incomplete connectivity, plain PZT particles were coated with carbon black of various weight fraction and the experiments were repeated. The results show there exists an optimal coating ratio of carbon black where the loss factor reaches its maximum value. When the optimal coating was applied to plain PZT particles, the loss factors of composites continuously increased, eliminating the threshold effect.

Loss of Post-Wall Waveguides and Efficiency Estimation of Parallel-Plate Slot Arrays Fed by the Post-Wall Waveguide in the Millimeter-Wave Band

Abstract: This paper presents the loss factors in the post-wall waveguide-fed parallel-plate slot array antenna in the millimeter-wave band At first, transmission loss is evaluated per unit length by measuring the losses of post-wall waveguides on various substrates with different thicknesses in different bands Measured results of the frequency dependence agree with theoretical predictions using the effective conductivity and the complex permittivity obtained by the whispering gallery mode resonator method Then the authors evaluate the antennas with various sizes at 765 GHz The antenna efficiency is evaluated by taking into account the loss factors related to: the transmission loss both in the feed and the parallel plate waveguides, the aperture efficiency and the insertion loss and the reflection of the transition Also, the loss due to the locally-perturbed currents by the slot radiation is evaluated The sum of the losses in the prediction quantitatively agrees with the measurement

Loss Factor Characterization Methodology for Piezoelectric Ceramics

Abstract: The key factor for the miniaturization of piezoelectric devices is power density, which is limited by the heat generation or loss mechanisms. There are three loss components for piezoelectric vibrators, i.e., dielectric, elastic and piezoelectric losses. The mechanical quality factor, determined by these three factors, is the figure of merit in the sense of loss or heat generation. In this paper, quality factors of resonance and antiresonance for k31, k33, and k15 vibration modes are derived, and the methodology to determine loss factors in various directions is provided. For simplicity, we focus on materials with ∞mm (equivalent to 6mm) crystal symmetry for deriving the loss factors of polycrystalline ceramics, and 16 different loss factors among total 20 can be obtained from the admittance/ impedance measurements.

Effect of constrained layers on vibrational characteristics of a composite sandwich system—A finite element based critical investigation

Abstract: The main aim of this paper is to investigate the effect of various constrained layers (viscoelastic layer (VEL), electro-rheological fluid (ERF), and magneto-rheological fluid (MRF)) over natural fre- quency and the damping loss factor with two different fiber orientations (0 and 90) for a Graphite/Epoxy (GR/E) composite sandwich shaft disc system. The finite element technique is used to investigate the natural frequency and loss factor for various combina- tions. Furthermore, the vibrational characteristics of the composite sandwich shaft disc system are compared with those of the base structure without constrained layers. The study shows that introducing various constrained layers reduces the magnitude of natural frequency by up to 80%. The results also show that GR/ E composite with 90 fiber orientation acquires the highest frequency reduction. Among the proposed layers, VEL has the highest damping loss factor.

Energy Dissipation by Micro-Slip in an Assembly, Analytic and Experimental Approach

Abstract: In structural dynamics, the problem of damping remains the biggest challenge. This paper deals with the energy losses caused by micro-slip in a planar interface of a structure. Taking into account friction in the joints during the analysis of dynamic systems remains a complex task. This paper proposes an analytical and experimental study of flexural vibrations of a clamped-clamped beam with innovative position of the interfaces. First, the benchmark is described and the choice of the position of the interface is justified. The displacement and stress fields are defined during each phase of the loading process in the joints under the assumption of quasi static motion. The energy dissipated by friction in the interface is calculated during a loading cycle. This leads to a definition of the dissipated energy, thus, to a non linear loss factor. The dynamic response of the beam is calculated using this non linear loss factor and a dissipative force is defined and used to predict the dynamic behaviour of the structure. In the last part of the paper, we present the experimental bench, and the dynamic behaviour of this structure. We propose to illustrate the mechanism of energy losses by micro-slip by making a comparison between the behaviour of the “monolithic” beam and the sectioned beam. Finally, we confront the loss factor calculated analytically and the measured one.Copyright © 2011 by ASME

Electrical properties of polyurethane-based composites

Abstract: In this study the effect of nano size borax fillers in polyurethane is investigated by evaluating its electrical properties; the relative permittivity, loss factor and dc conductivity. The particle size of borax fillers used in this study is 70 nm. The borax filler/TPU composites were prepared with 1% by weight of filler content. Evaluation of conductivity, loss factor and dielectric constant is performed using a high voltage testing kit. For evaluating the conductivity of the material, high voltage dc source was used, while for determining the dielectric constant and loss factor a high voltage ac source operating at 60 Hz was employed. The nanocomposite with 70 nm particle size and a concentration of 1% by weight borax filler indicated a lower dc conductivity and relative permittivity than of pure TPU. The measured value of loss factor is higher than that of pure TPU samples.

Longitudinal geometric loss factor and impedance of a step-out discontinuity at arbitrary beam energy in a round cylindrical beam-pipe

Abstract: Using exact field matching, the longitudinal loss factor and impedance of a step-out in a round cylindrical beam-pipe at arbitrary beam energy have been obtained analytically. The beam-pipe sections have perfectly conducting walls which are connected coaxially at z =0 such that b 2 b 1 , where b 2 and b 1 are the corresponding radii. Comparison between the step-out and step-in impedances at ultrarelativistic energies shows that both impedances peak at the same eigenmode frequencies. The imaginary parts of the step-out and step-in impedances are negative, slightly different in magnitude up to few Ohms, and have a similar frequency evolution. The real part of the step-out starts at positive values below the first cut-off, remains positive and tends toward a positive value at higher frequencies. At low frequencies below the first cut-off frequency, the real parts of the step-out and step-in impedances are equal in magnitude, shifted up to a positive value for the step-out and down below zero to the same value for the step-in. Numerical examples of the variation of step-out impedance with beam energy have also been given. The loss factor of the step-out is positive indicating energy loss, is higher in magnitude than the negative loss factor of the step-in, and therefore, the net effect will be a slowing down of the beam.

Study on Dynamic Properties of Molybdenum-catalyzed Branched HVPBR

Abstract: The dynamic properties of molybdenum-catalyzed branched HVPBR(b-HVPBR) were studied by using rubber processing analyzer(RPA2000),and compared with those of BR,ESBR and SSBRThe results showed that,in the range of experimental frequency,the storage modulus(G′) of b-HVPBR was the highest under low frequency,the loss modulus(G″) and loss factor(tanδ) were smaller than those of BR,ESBR and SSBR,respectively,and their complex viscosity(η*) showed the same trait with that of pseudoplastic fluidIn the range of experimental temperature or strain,the G′ of b-HVPBR was higher than that of BR,ESBR and SSBR,and the tanδ was smaller

Damping Properties of Viscoelastic Stiffened Laminated Cylindrical Shells with an Unconstrained Fiber-Reinforced Layer

Abstract: By use of the mixed layerwise theories and the interpolation functions of displacements and transverse stress, the dynamics equations of viscoelastic stiffened laminated cylindrical shells with an unconstrained fiber-reinforced layer were derived. The predicted vibration frequency and loss factor show the good agreement with the A.Okazaki’ experimental results for the two-layer cylindrical shells. The non-dimensional frequencies and loss factors were computed for different Young’s modulus and thickness of viscoelastic layer. The results show that using a higher module and thickness viscoelastic layer can effectively increase the loss factors; moreover, using a circular-reinforced viscoelastic layer has little effect on the non-dimensional frequencies, but can effectively increase the model loss factors.

Loss Factor of Tapered Structures for Short Bunches

Abstract: Using the electromagnetic simulation code ECHO, we have found a simple phenomenological formula that accurately describes the loss factor for short bunches traversing an axisymmetric tapered collimator. In this paper, we consider tapered collimators with rectangular cross-section and use the GdfidL code to calculate the loss factor dependence on the geometric parameters for short bunches. The results for both axisymmetric and rectangular collimators are discussed. The behaviour of the impedance of tapered structures for very short bunches in the optical regime has been determined in refs. [10,11]. Here, for the loss factors for two particular geometries, we have studied the departure from the optical regime behaviour as bunch length is increased. In both cases, the ratio of the loss factor for the tapered collimator to the loss factor in the optical regime is a function only of the scaling parameter {sigma}L/d{sup 2}. The fact that the bunch length a and the taper length L appear as a product is consistent with the recent scaling derived by Stupakov in ref. [12], since there is only a weak dependence on g. One noteworthy fact that is not a priori expected is that only the larger radius or vertical half-aperture d appears. The more » reduction factor is independent of b. Moreover, it is striking that the specific form involving the arctan given in Eq. (5) holds for both geometries, with only the coefficient {mu} differing by a factor of {approx}2 for flat vs round. This suggests that there may be a useful phenomenological form for more general geometries which may follow from natural extensions of Eq. (5). This possibility is presently being investigated. « less

Damping Loss Factor Estimation for Coupled Plates Using Experimental Transient Statistical Energy Analysis

Abstract: Damping loss factors and coupling loss factors are estimated for two sets of coupled plates, one set joined along a line and the other joined at a point. Two levels of damping, achieved with constrained layer treatments are considered. For the more highly damped plates, the differences between estimations using transient force versus persistent force are small. As expected serious differences in estimated loss factor are found for lightly-damped plates, that is, with loss factors below 0.01 (1%).

Damping Optimization of Composite Structures with Multi-interleaved Viscoelastic Layers

Abstract: For the damping optimization of composite structures with multi-interleaved viscoelastic layers,a computational model is built for the loss factor by the energy method,in which the strain energy stored in the in-plane as well as in transverse shear is considered,and its deflection function is assured to be perfect by means of an experimental method.The optimization goal is the maximum of the loss factor of composite structures with multi-interleaved viscoelastic layers.Optimization designs are made of a single variable and multi-variables optimization for the loss factor by improved genetic algorithms.The numerical results show that the improved genetic algorithms are available for the damping optimization design of composite structures with multi-interleaved viscoelastic layers,and that the multi-variable optimization design is better than single variable optimization design.After the damping optimization design,the loss factor of composite structures with multi-interleaved viscoelastic layers is improved from the original result of 0.184 to 0.287.

Parametric Instability of a Sandwich Beam with an Electrorheological Fluid Core Subjected to Various Boundary Conditions

Abstract: In the present study, the parametric instability of a three layer sandwich beam with an embedded electrorheological (ER) fluid core has been studied under various boundary conditions, namely fixed-fixed, pinned-pinned, fixed-free, and fixed-pinned. The beam has been modeled using finite elements and the regions of instability have been established using Saito and Otomi conditions. The ER core model is based on the pre-yield rheological properties and is represented by the complex shear modulus. The sandwich model is based on shear configuration. The effects of the electric field, shear parameter, and core thickness parameter on the fundamental frequency, fundamental buckling load, and fundamental system loss factor have been investigated. The effects of different parameters, such as the electric field, shear parameter, thickness parameter, and static load factor on the stability behavior of the beam have been investigated. Increasing the electric field strength, core thickness ratio, and shear parameter has a stabilizing effect for all the boundary conditions; by contrast, increasing the static load factor has a destabilizing effect for these support conditions.

Dynamic characteristics analysis of constrained damping pipe and its application

Abstract: The mathematical model of constrained damping pipe for device supporting and vibration reduction was established.The analytical expressions of displacement,dynamic stiffness and loss factor of the damping pipe with respect to geometric and physical parameters were obtained.The results show that the length of damping layer has significant effect on loss factor and there is an optimal length which makes loss factor a max value when other structural parameters maintain unchanged.It provides a quick and convenient optimization method to design damping pipes.

Sound transmission loss improvement by a viscoelastic material used in a constrained layer damping system

Abstract: A constrained layer damper is a viscoelastic material that is embedded between two parallel plates. The vibration energy in the first leaf creates shear strain in the viscoelastic material which dissipates kinetic energy into heat. A CLD is an effective way to maximize transmission loss through a partition by increasing its damping. SEA is a method for estimating the acoustic power flow through a system. The method subdivides the system into smaller elements, the so-called subsystems, that support a group of resonant modes and have a sufficient modal density and modal overlap. The measurement of the loss factors on the wall specimens with and without the viscoelastic material was done as part of a parallel paper by J.G. Richter. The reverberation method was used to measure the total loss factors on one side of the installed wall. The addition of a viscoelastic material between the leaves improves the TL significantly by more than 10 dB in the mid- and high frequency range increasing the STC rating by 8 points from 44 to 52.

Optimization of structural parameters using artificial neural network for vibration reduction in beams

Abstract: Recently optimization of structural parameters like stiffness coefficient and damping coefficient, using artificial neural network for vibration reduction in beam has become a major application in aerodynamics and many other fields By placing the PVC dampers of different cross sectional area at different locations along a beam, we have to minimize the response and the response time of the beam due to vibrations Measuring factor of damping (reduction in vibration) is the LOSS FACTOR (Ω) for the system Along the beam, where the loss factor is more, it gives us an optimal position for placing the damper It also gives stability to the structure The stability of the beam enhances due to increase in core loss factor also

Damping Properties of Viscoelastic Laminated Plates with an Unconstrained Fiber-reinforced Layer

Abstract: Applying the mixed layer wise theories and Ressiner’s mixed variational theorem, the dynamics equations of viscoelastic laminated plates were deduced and the numerical solutions for simple-support laminated plates were derived through Navier solutions. Computing the natural frequency and the loss factor in the plates corresponding to the lower-rank models and analyzing the viscoelastic layer' influence on the damping properties, the results show that the non-dimensional frequency and the loss factor will increase with higher Young’s modulus of a viscoelastic layer. Using a fiber-reinforced viscoelastic layer has little effect on the non-dimensional frequency, but can effectively improve the damping characteristic and reduce the resonance amplitude of transverse displacement.

Calculation and Analysis of Loss Factor of Building Materials

Abstract: In order to describe the damping characteristics of building materials and members, the formula for calculating loss factor which concerns with the internal loss factor and edge losses was derived from the concise physical relationship and, calculations of loss factor of some common building materials and members are presented. Therefore, the loss factor curves of among the walls which made of different materials are gained. It is shown that at low frequency total loss factor (damping) of a building material gradually decreases with the frequency and is also dependent on the thickness of the wall and its longitudinal wave speed, and at high frequency it tends to a constant.

Vibration Transient Response Using Statistical Energy Analysis

Abstract: Transient Statistic Energy Analysis (T. S. E. A.) for transient response of a vibration system is investigated in this paper. Mathematical expressions of the rise time and the peak energy were derived. Numerical modeling of the system was also made. It showed that the peak energy decrease as the internal loss factor and the coupling stiffness decrease, the rise time decease as the internal loss factor and the coupling loss factor increase. It was found that the results of TSEA and the traditional methods are identical.

Study of the Measurement of Young's Modulus and Loss Factor for a Viscoelastic Damping Material Using a Multi Degree of Freedom Curve Fitting Method and RKU Equation

Abstract: Offshore structures, such as a platform, a buoy, or a floating vessel, are exposed to several dynamic loads, and viscoelastic damping material is used to reduce the vibration of offshore structures. It is important to know the properties of viscoelastic materials because loss factor and Young's modulus of the viscoelastic damping material are dependent on frequency and temperature. In this study, an advanced technique for obtaining accurate loss factor and Young's modulus of the viscoelastic damping material is introduced based on a multi degree of freedom curve-fitting method and the RKU (Ross-Kerwin-Ungar) equations. The technique is based on a modified experimental procedure from ASTM E 756-04. Loss factor and Young's modulus of the viscoelastic damping material are measured for different temperatures by perfor ming the test in a temperature-controlled vibration measurement room where temperature varies from 5 to 45 degrees Celsius.