Showing papers on "Loss factor published in 2013"

Effect of Cross-Link Density of the Matrix on the Damping Properties of Magnetorheological Elastomers

Abstract: The effect of cross-link density of the matrix on the controllable damping properties of magnetorheological elastomers (MREs) has been investigated. MRE samples with different cross-link densities and plasticizer contents were fabricated and their microstructures were observed using an environmental scanning electron microscope (SEM). The dynamic performances of these samples were measured using a modified dynamic mechanical analyzer (DMA). The experimental results indicated the magneto-induced change of loss factor was enhanced by decreasing the cross-link density. The plasticizer and the frequency markedly influenced the magneto-induced change of loss factor when the cross-link density of the matrix was low. In addition, by reducing cross-link density, the magneto-induced modulus and the relative MR effect increased. A mechanism for the magneto-induced change of loss factor was proposed and the analysis implied that the rearrangement of particles is an important influence on controlling the damping prop...

Analysis and optimal design for the damping property of laminated viscoelastic plates under general edge conditions

Abstract: The present paper is concerned with analysis and optimal design for the damping loss factor of laminated plates under general edge conditions. In the analysis based on the classical lamination theory, the loss factor is deduced from the energy formulation for symmetrically laminated thin plates comprised of fiber reinforced layers and viscoelastic layers. The effects of location and thickness of viscoelastic layers are studied on the loss factor of the plates, and those of the fiber orientation angles are also clarified. In the optimal lay-up design problem, a layerwise optimization (LO) method is applied to the plates comprised of two different orthotropic materials, and the optimal fiber orientation angles are determined to obtain the maximum loss factor in the fundamental mode. These numerical simulation results uncovered that the present approach is quite useful in analyzing and designing the loss factor of the plates.

Measuring the complex modulus of polymers by instrumented indentation testing

Abstract: Instrumented indentation is used to measure the complex modulus of highly plasticized polyvinyl chloride (HP-PVC) and four kinds of polyethylene over the frequency range of 1–50Hz. Over this range, the loss factor for the HP-PVC increases from 0.3 to 1, making this an ideal material for damping out noise and vibration. The storage moduli for the four polyethylene samples are ordered according to density, with the lowest-density material have the lowest storage modulus. Results for both storage modulus and loss factor compare well with published results obtained by dynamic mechanical analysis for nominally similar materials.

Dependence of the dynamic properties of Voigt and Reuss composites on the Poisson's ratios and bulk loss factors of the constituent materials

Abstract: Materials possessing both high stiffness and high damping would be beneficial in many structural applications. Composites that combine a stiff material, which usually has low damping, with a soft and lossy material have been proposed to engender both high dynamic modulus and high loss factor. In this article, we investigate the effective dynamic moduli and loss factors of Reuss and Voigt composites in response to a uniaxial harmonic load. The constituent materials are characterized by multiaxial viscoelastic models in the frequency domain. Using the viscoelastic correspondence principle, we derive formulae for Reuss and Voigt composites of infinite dimensions taking into account Poisson effects. We show that the effective loss factor of a Reuss composite is sensitive to the values of the Poisson's ratio and bulk loss factors of the constituent materials. Finally we simulate, using finite element analysis, the response of cylindrical Reuss composite rods of finite radius to an axial load. We demonstrate th...

Experimental investigation on shape memory alloy metal rubber

Abstract: Shape memory alloy metal rubber (SMAMR) is a novel intelligent elastic damping material which can realize the integration of structure and function. The investigations on the anisotropic mechanical characteristics which depended on shaping craft and working temperature were conducted by quasi-static tests. Comparative experiments indicated that the heat setting temperature affect the elastic modulus non-monotonously but has little effect on the loss factor of SMAMR in both martensite and austenite phases. With the increase of the heat setting time, the elastic modulus of SMAMR monotonously decreases and the reduction of loss factor is unobvious. With the present shaping craft, SMAMR exhibits the anisotropy in moulding and non-moulding directions, which is affected by the heat setting process and working temperature. It was proved that the mechanical properties have approximately linear relationship with temperature during the phase transition process. Due to its temperature-dependent mechanical properties, SMAMR that experiences the heat setting procedure is expected to be used in active vibration control systems with varying temperature-dependent stiffness and damping coefficients to provide superior vibration control performance.

Loss factor and impedance analysis for the diamond storage ring

Abstract: Diamond Light Source is investigating the possibility of increasing the storage ring operating current above the nominal 300 mA. A campaign of measurements and simulations has been carried out in order to understand the extent of the parasitic energy loss and characterise the most important items which build up the machine impedance. In this paper we report on the most recent measurements of the longitudinal loss factor and the present status of the impedance database with an initial comparison between the two.

Vibration characteristics of orthotropic shaft–disk system with different constrained damping layers: experimental and numerical study

Abstract: This paper reports the results of an investigation carried out to study the effect of various constrained layers (viscoelastic layer (VEL), electrorheological fluid, and magnetorheological fluid) on natural frequency and damping factor. The different fiber orientations (0°, 30°, 45°, 60°, and 90°) were considered for glass/epoxy (G/E) and graphite/epoxy (GR/E) shaft–disk systems. Experimental evaluation and finite element technique are employed to investigate the natural frequency and damping factor for various combinations. The vibrational characteristics of the composite sandwich shaft–disk system are also compared in this present study. From the study, it is evident that the VEL core shows excellent frequency and damping loss factor performances, and the 90° fiber-oriented composites are dominant in vibration damping performances. The GR/E shaft–disk system outperforms the G/E shaft–disk system.

Comparative Study about the Damping Properties of the Sandwich Beams with Core by Polystyrene or Polypropylene Honeycomb

Abstract: Starting from the dynamic response of a sandwich beam with damping (which is in free vibration), is established a method used to determine the damping factor. We experimentally calculated the stiffness and damping factor per unit length and unit mass for beams with middle layer made of polystyrene and polypropylene honeycomb respectively; the external layers were made of epoxy resin reinforced with fiber- glass fabric and carbon-fiber fabric respectively. systems. The analysis is based on a proper splitting of the damping operators in both the field equations and the boundary conditions. The purpose of research done in (16), was to investigate the curvature, and the face / core debonding influence on the vibration behaviour of curved composite sandwich beams built from carbon / epoxy laminate skins over a foam polyurethane core. The sandwich-type beams, flat and curved, with debonding, were prepared by keeping of the arc length of the sandwich beams, equal to the length of flat sandwich beams. Natural frequencies and damping loss factor, for sandwich beams, were determined using impulse frequency response technique under free-free boundary conditions. The paper (17) presents a numerical investigation of changes to natural frequencies due to the separations along the line of solder in a composite sandwich beam (as a fascicle of stratified fiber). The numerical analysis is made using the link elements (rigid links and master slave links). The analysis is done using finite element method. Recent applications have shown that honeycomb panels from polymer, reinforced with fiber, can be used for new construction or for restoration of existing structures. In (18) are studied the vibrations of sandwich structures with honeycomb which have the core geometry of sinusoidal type. It was developed a higher order vibration model for studying the vibrations, made by energy methods. In (19) were investigated the free vibrations of the curved sandwich beams, with flexible core, in different conditions of temperature. The external surfaces and the core of the beam were considered as being made of materials with mechanical properties dependent on temperature. It was shown that the frequency of free vibrations of the beams decreases when the temperature increases. Theoretical aspects The movement equations for the transversal vibrations of the viscoelastic beams, with constant section, and

Development of Polyimide Foam for Aircraft Sidewall Applications

Abstract: In this paper, the use of polyimide foam as a lining in double panel applications is considered. It is being investigated here as a replacement for aircraft grade glass fiber and has a number of attractive functional attributes, not the least of which is its high fire resistance. The test configuration studied here consisted of two 1mm (0.04 in.) thick, flat aluminum panels separated by 12.7 cm (5.0 in.) with a 7.6 cm (3.0 in.) thick layer of foam centered in that space. Random incidence transmission loss measurements were conducted on this buildup, and conventional poro-elastic models were used to predict the performance of the lining material. Results from two densities of foam are considered. The Biot parameters of the foam were determined by a combination of direct measurement (for density, flow resistivity and Young s modulus) and inverse characterization procedures (for porosity, tortuosity, viscous and thermal characteristic length, Poisson s ratio and loss factor). The inverse characterization procedure involved matching normal incidence standing wave tube measurements of absorption coefficient and transmission loss of the isolated foam with finite element predictions. When the foam parameters determined in this way were used to predict the performance of the complete double panel system, reasonable agreement was obtained between the measured transmission loss and predictions made using a commercial statistical energy analysis code.

Research the Influence of Curved Shape on the Multilayer Bellows

Abstract: As a cylindrical thin-walled container, multilayer bellows has greater bit shift compensation, vibration and noise reduction capabilities while the appropriate metal and viscoelastic damping materials are adopted. Finite element models are adopted to analyze the loss factor of multilayer bellows in ANSYS. The strain energy distribution of Multilayer bellows and viscoelsticity layer are given. According to the strain energy, the influence of structural parameters on the loss factor is studied. The results show that the loss factor can be improved by employing the curved shape with big wave height, small wall thickness, small wave pitch and diameter of bellows.

A comparison of different methods for determination of coupling factor and velocity response of coupled plates

Abstract: Coupling loss factors (CLF) and velocity responses has been computed for two plates joined in a ‘L’ junction configuration using Statistical Energy Analysis. The analyses have been carried out to study the effects of internal loss/damping factor on the coupling factors. The effects of plate widths on the coupling factors and velocity responses at high frequencies has also been studied. The statistical energy parameters have been computed using analytical wave approach, finite element method and Free-SEA software. The studies have revealed that the coupling factor computed by the wave approach is independent of the internal loss factor as compared to the values computed using finite element method, wherein CLF increases linearly as the internal loss factor varies from a zero value, followed by a transition region and converges to the values obtained by the analytical wave approach and remains insensitive to changes at higher values of damping. The results obtained from the studies signify the effects of internal loss/damping factor and plate widths on proper selection and usage of the above mentioned methods for the estimation of coupling factors and velocity responses using statistical energy approach.

A study of damping characteristics of alumina-filled epoxy nano-composites

Abstract: Damping behavior of polymeric composites with nano structured phases is significantly different from usual polymer composites. Viscoelastic homopolymers exhibit high material damping over a relatively narrow range of temperature and frequencies. In many practical situations a polymeric structure is required to possess better strength and stiffness properties together with a reasonable damping behavior. Viscoelastic polymers show higher loss factor beyond the glassy region which comes with a significant drop in the specific modulus. Addition of nano alumina particles to epoxy leads to improved strength and stiffness properties with an increase in glass transition temperature while retaining its damping capabilities. Experimental investigations are carried out on composite beam specimen fabricated with different volume fractions of alumina nano particles in epoxy to determine loss factor, tan δ. Impact damping method is used for time response analysis. A single point Laser is used to record the transverse displacement of a point on the composite beam specimen. Experimental results are compared with theoretical estimation of loss factor using Voigt estimation. The effect of interphase is included in theoretical estimation of loss factor. Passive vibration suppression may be introduced in the polymeric structures along with improved structural properties by tailored dynamic characteristics using nano alumina particle filled epoxy composites.

Loss components in electrical steel with Goss texture

Abstract: The determination of the specific power loss separation of electrical steel sheets in different direction to rolling direction have been performed using non-standard single sheet tester. Specific total loss was separated into hysteresis, eddy current and excess loss components. The relationship between the hysteresis and additional loss components as well as between additional loss factor and the magnetic anisotropy was analyzed.

Bendable Electro-Acoustic Transducer Fabricated Utilizing Frequency Dispersion of Elastic Modulus

Abstract: To realize the speaker diaphragm that can be united with a flexible display without deteriorating lightweight properties and flexibility, a novel bendable electro-acoustic transducer (BEAT) based on 0–3-type piezoelectric composites has been developed. To overcome the trade-off between flexibility and the transmission efficiency of vibration energy, a viscoelastic polymer that has local maximum points in the loss factor as well as large frequency dispersion in the storage modulus near room temperature was employed as the matrix of the piezoelectric composite layer. Against the comparatively slow (10 Hz or less) deformation from the outside, the viscoelastic matrix is viscous enough to prevent cracking and delamination. On the other hand, in the audible range (20 Hz to 20 kHz), the matrix is elastic enough to transmit piezoelectric vibration energy, maintaining a moderately large loss factor as well as a high sound velocity. For the first time, we successfully demonstrated a rollable speaker that can continue to generate a high-quality sound while being rolled and unrolled repeatedly onto a cylinder with a curvature radius of 4 mm.

Normalized stiffness ratios for mechanical characterization of isotropic acoustic foams

Abstract: This paper presents a method for the mechanical characterization of isotropic foams at low frequency. The objective of this study is to determine the Young's modulus, the Poisson's ratio, and the loss factor of commercially available foam plates. The method is applied on porous samples having square and circular sections. The main idea of this work is to perform quasi-static compression tests of a single foam sample followed by two juxtaposed samples having the same dimensions. The load and displacement measurements lead to a direct extraction of the elastic constants by means of normalized stiffness and normalized stiffness ratio which depend on Poisson's ratio and shape factor. The normalized stiffness is calculated by the finite element method for different Poisson ratios. The no-slip boundary conditions imposed by the loading rigid plates create interfaces with a complex strain distribution. Beforehand, compression tests were performed by means of a standard tensile machine in order to determine the appropriate pre-compression rate for quasi-static tests.

An order estimation of the acoustic losses inside a simulated liquid rocket chamber

Abstract: Acoustic losses inside a simulated liquid rocket chamber are investigated by numerical simulation coupled with theoretical calculation. In this study, the losses by injector, resonator and chamber are considered and compared. The oscillation amplitude is assumed to be small (within linear range). For injector and chamber, the loss mechanisms, such as the radiation & convection from the inlet or outlet, and viscous & thermal loss at the wall are considered. For a resonator, the viscous & thermal loss would be the major loss factor. A simulated liquid rocket chamber configuration with an injector installed off-center is investigated especially for tangential oscillation modes. It is found that with well-tuned resonator the resonant frequencies and modes would change from those without the resonator. Therefore, the coupled simulation is indispensable for resonator design. Also an order estimation of each acoustic loss factors is conducted. It is found that the viscous & thermal loss of the chamber and resonator dominate the total acoustic loss in the present configuration. However, if several hundreds of injectors is equipped as in actual rocket chamber, the loss related to injectors would become comparable to that related to resonator on the total loss.

Evaluation of Loss Factor Estimation Techniques for Free Hanging Flat Panels Excited Mechanically

Abstract: To establish the "best" technique to estimate a damping loss factor for mechanically-excited panels, three loss factor estimation techniques – PIM, IRDM, and RDT – are compared. In experimental and computational analyses, panels with two damping levels and three sizes were tested. The loss factor estimates from each of the three techniques are then evaluated in four distinct frequency bands centered at one-third octave frequencies of 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz (for computational analysis only). Unlike IRDM and RDT, the quality of PIM-based loss factor estimates have presented a strong correlation between the region of response measurement and it is distance from the excitation location. PIM-based loss factors were significantly underestimated when responses are measured inside the direct field. PIM-based loss factors are relatively accurate only if the measurements are made from wide-spread response locations. For a lightly damped panel, loss factor estimates using PIM, IRDM and RDT with direct averaging agree within reasonable accuracy. For intermediately to highly damped panels, IRDM and RDT with direct averaging under-predicted the loss factor; RDT with an autocorrelation function averaging approach slightly over-predicted the loss factor. Both RDT approaches might be used to set a bound on panel loss factor. Even when significantly fewer response locations are considered, it is evident that loss factor estimates from RDT are as reliable as IRDM and more reliable than PIM especially for highly damped panels. For the analysis of freely hanging plates, excitation "close to an edge", especially for PIM, is not recommended. When analyzing the panel loss factor, arbitrary or central excitation is acceptable.

Optimization of the damping properties of CFRP laminates with embedded viscoelastic layers

Abstract: This paper addresses the problem of improving the loss factor of carbon-epoxy laminates with embedded viscoelastic layers. A cork based agglomerate was elected as viscoelastic material due to its low weight combined with excellent damping properties, showing a great potential for vibration control. A micro-sandwich type geometry was adopted as this provides a good compromise between structural efficiency and easiness of inclusion of the damping material. A numerical model was developed in order to obtain the best material configuration in terms of its damping response. Distinct design variables were considered to assess their influence in the loss factor variation, namely: damping layer thickness and its relative position within the laminate, number of viscoelastic layers and effect of different layup stacking sequences. Numerical results were compared with experimental data as this was a determinant step to obtain accurate computational models regarding the different types of geometries. Results are encouraging for the possible use of cork based composites as a viable passive solution to improve the damping properties of high performance composites, giving rise to an increase of the loss factor as well as a change of the natural frequencies of the structure according to the design requirements for particular applications.

The Study of High Frequency Vibration in Complex Coupling Structure via GM(h,N) Method

Abstract: With the development of technology, people almost have solved the problems caused by low-frequency vibration in the mechanical field. However, the problems caused by the high frequency vibration are not solved at present. Hence, the paper is based on the consideration of high frequency vibration impact factors, and it uses the GM(h,N) model in the grey system theory to identify the degree of impact factors of panel-beam coupling structure. Through pasting the mass onto panel-beam coupling structure randomly, it changes the structure of body mass, rigid and damping size. Also, according to the test, it adjusts the simulation model to ensure the correctness of the simulation model. In the simulation software Autosea2, it changes the parameters of mass, stuff and damping randomly, and it reaches the response values of the system. Next, the GM(h,N) method in the grey system theory is used to calculate the weighting of each influence factor. The results show that damping loss factor of the framework has greater influence on high frequency vibration response values, followed by damping loss factor of the panel, and tensile modulus has the least influence. It can be concluded that during the process of making and using panel-beam coupling, the main focus is to consider the properties of the materials based on resolving connection problems. We try to control the damping loss factor changes in different connecting ways to reduce the impact of the structure. The reached conclusion can be the reference to other relevant panelbeam coupling high frequency vibration.

A new structural wave number method to measure the dynamic characteristic parameters of viscoelastic damping material

Abstract: For the viscoelastic damping material to possess excellent dissipating performance, it is crucial to obtain the dynamic characteristic parameters (DCP) of viscoelastic damping material exactly and effectively, and then to make it as input data for numerical analysis and design in the control of structural vibration. For this sake a new measurement method is presented to acquire the DCP of the viscoelastic damping material effectively in the manuscript. The properties of damping material can be achieved by substituting tested wave numbers or loss factor of composite viscoelastic damping beam (CVDB) into its inversion process of complex bending stiffness. In the present study, the loss factor of beam with unconstrained viscoelastic damping layer is measured by McDaniel and attenuation methods, respectively. And those results are compared with each other to certify the accuracy of test results firstly. Then influences of test conditions on loss factors derived from McDaniel method are studied to give some advices in the measurement. Finally the DCP of the viscoelastic damping material are obtained by the new method with complex wave number and compared with those obtained by using the resonance beam method. From the comparison it is concluded that the present proposed new approach can use limited samples to measure the DCP of the viscoelastic damping material in a wide range of frequencies effectively and conveniently.

Dynamic stability analysis of a sandwich beam with functionally graded material constraining layer

Abstract: The present work aims to study the dynamic stability of a three layer sandwich beam with viscoelastic core and functionally graded material constraining layer. Sandwich beam is modelled as a line element having two nodes of each having four degrees of freedom. Finite element method is used to model the beam. Variation of properties of functionally graded material is taken according to a simple power law. The Hsu’s procedure proposed by Saito and Otomi has been used to determine boundaries of stable and unstable regions of the sandwich beam. The effect of various system parameters such as core thickness ratio, power law index, core loss factor etc., on the dynamic stability of the sandwich is studied theoretically. For the fixed- free sandwich beam buckling load decreases with increase in power law index. The frequency parameter first decreases and then increases for increase in power law index and core thickness ratio parameter. Fundamental loss factor of sandwich beam increases with increase in the core loss factor. Increase in core thickness ratio, first decreases and then increases the fundamental loss factor. Increase in power law index values, shows more probability of instability of beam. Increase in thickness ratio also enhances the instability chances of sandwich beam.

Research on Measurement Method for Loss Factor of Viscoelastic Material

Abstract: A measurement method for loss factor of viscoelastic material was researched. When acoustic wave incident to the surface of submerged elastic plate coated with viscoelastic damping layers, according to boundary conditions of interfaces relationship between reflection acoustic wave in water and loss factor of viscoelastic material was derived. The change of loss factor as frequency goes was also simulated. Loss factor is related to frequency and other parameters of viscoelastic material.