Showing papers on "Loss factor published in 1999"

Viscoelastic properties of MR fluids

Abstract: Mechanical properties of magnetorheological (MR) fluids are classified into pre-yield and post-yield regions according to whether the shear stress is below or above the yield stress. MR fluids within the pre-yield region exhibit viscoelastic properties; and these properties are important for understanding MR suspensions, especially for vibration damping applications. MR suspensions composed of reduced iron powders dispersed in silicone oil are utilized to study the viscoelastic properties with the help of a strain-controlled rheometer with plate-plate configuration. Two types of experiments, i.e. strain-amplitude sweep mode and frequency-sweep mode, were carried out to investigate the viscoelastic properties of MR fluids: (a) strain-amplitude sweep mode, the strain amplitude was swept from 0.0001 to 0.001 at a fixed driving frequency of 10 Hz. (b) Frequency-sweep mode, the driving frequency was swept from 1 Hz to 100 Hz at a constant strain amplitude of 0.001. The results show that both storage modulus G´ and loss modulus G´´ decrease with the increment of the strain amplitude, however, the loss factor increases with the increment of the strain amplitude. On the other hand, both the storage modulus and loss modulus increase with the increment of frequency, which is different from the loss factor. Moreover, the effects of magnetic field and volume fraction on the viscoelastic properties are also investigated. The higher the magnetic field, the higher the storage modulus and loss modulus, and the lower the loss factor. The higher the volume fraction, the higher the storage modulus and the loss factor.

Preparation and microwave characterization of baxsr1-xtio3 ceramics

Abstract: BaxSr1-xTiO3 ceramics have been synthesized by a conventional solid-state reaction for x=0.2, 0.4, 0.6, 0.8. The phase constitution was examined by X-ray diffraction. The microwave dielectric properties of BaxSr1-xTiO3, such as the real part of the relative dielectric constant and loss factor, were measured by the postresonator method on the TE011 resonant mode for the different compositions. The real part of the relative dielectric constant varies from 200 to 900, with a loss factor from 10-3 to 10-2 at a resonant frequency of approximated 2 GHz.

Vibration analysis and control of flexible beam by using smart damping structures

Abstract: The temperature effects on frequency, loss factor and control of a flexible beam with a constrained viscoelastic layer and shape memory alloy layer (SMA) are discussed. It is shown that the temperature in the SMA (actuation) layer is very important in the determination of frequency and loss factor of such a structure. The effects of damping layer shear modulus and damping layer height as affected by the temperature are also discussed. As temperature plays such an important role, it is, therefore, imperative to evaluate temperature effects on the control of the system as well. Results with and without active control are discussed.

On the loss factor of wood during radio frequency heating

Abstract: The radial direction loss factor of full-size western hemlock sapwood and heartwood, as well as western red cedar heartwood timbers was measured using the direct calorimetric method with a laboratory-scale radio frequency/vacuum dryer at the frequency of 13.56 MHz, moisture content range between 10 and 80%, temperature range between 25 and 55 °C, and root mean square (rms) electrode voltages of 0.8 and 1.1 kV, respectively. The results indicated that the moisture content, temperature, electric field strength and wood type significantly affected the loss factor. Empirical regression equations were derived based on the experimental data that made possible the calculation of the loss factor and power density within wood during RF heating.

Application of Total Loss Factor Measurements for the Determination of Sound Insulation

Abstract: The influence of the total loss factor of building elements on their sound insulation is well known, although the problem of measuring this value was up to now not solved completely.This article describes an improved measuring method for total loss factors of building products especially for heavy elements. Furthermore, the principle of conversion of different results for transmission loss of the same type of wall under different mounting conditions using the total loss factor is presented. Measurement results in a transmission suite were examined and corrected with values derived from the improved measuring method.

Vibration control sheet and vibration control structure

Abstract: PROBLEM TO BE SOLVED: To provide a vibration control sheet and a vibration control structure to be regulated in the Young modulus and the loss factor of a viscoelastic member. SOLUTION: A viscoelastic material of a vibration control sheet stuck on the vibration portion of a member to be vibrated is prepared such that a basic material containing a base selected from secondary amine, tertiary amine, and a nitrogen-contained heterocycle is blended in a base polymer having a polar group or a chain on the polarity side and an acid material is further blended when occasion demands. A filler, such as mica, is blended in the viscoelastic material such that the viscoelastic material in a non-constrained type is set to a value within a range of a Young modulus of 1.0×10 dyn/cm or more and a loss factor of 0.01 or more and the material in a constrained type is set to a value within a range of a Young modulus of 1.0×10 dyn/cm or more and within a range of a loss factor of 0.0001 or more.

Loss factor Dependence on Group Velocity in Disk-Loaded Travelling- Wave Structures

Abstract: The loss factor, a quantity linked to the energy lost by a point-like charge when traversing an accelerating (or decelerating) structure, can be computed using programs which solve Maxwell’s equations in time domain and provide the correct result within the limitations inherent to the numerical simulation process. An alternative method, commonly used, consists in the derivation of the loss factor from the parameter R/Q, which is computed using codes operating in frequency-domain. Recent calculations of the loss factors for disk-loaded structures performed with the two methods have produced diverging results. The discrepancy of the results is a function of the group velocity and can be eliminated by introducing a correction term in the formula linking the loss factor to the R/Q obtained from frequency-domain calculations.

Additional loss due to operation of machines from inverters

Abstract: This paper presents a measurement method for determining the extra harmonic loss in an induction machine fed from a PWM inverter whilst the machine is running under any defined operating condition. The method allows the loss due to different harmonic frequencies to be segregated and enables a harmonic loss factor to be defined which can be used for loss prediction. Results are given confirming the accuracy of this prediction for a wide range of operating conditions. Particularly interesting features of the measurements are the variation of loss with load and the relatively large magnitude of the high frequency loss. Conventional equivalent circuit models predict neither of these effects.

Flexural Damping predictions of Mechanical Elements designed using Stress Coupled, co-cured damped Fiber Reinforced composites

Abstract: Light weight, dynamically stiff composite structures with out-of-plane damping levels in the range of 10%- 20% have been demonstrated. A computer model has been developed which will allow prediction and design offlexural modulus and loss factor for a single damping layer in a structure. The structures are created using viscoelastic material sandwiched between orthotropic composite layers. The composite layers have different orientation angles, purposefully unsymmetric. Stress coupling between the stiffness layers when excited by in-plane and or out-of-plane vibrations produces hysteresis losses that are distributed throughout the viscoelastic layers, resulting in vibrational damping. This paper is a follow-on to Improved Axial Damping of Mechanical Elements through the used of Multiple, Layered, Stress Coupled, Co-cured Damped Fiber Reinforced Composites.

Piezoelectric dispersion type org. composite damping material

Abstract: PROBLEM TO BE SOLVED: To obtain a damping material having a loss factor tan δ of 1 or more and low strain amplitude dependence. SOLUTION: The material comprises an org. dielectric or ferroelectric dispersed in a non-dielectric polymer pref. in the form of needles. The length-to- diameter ratio of the dielectric or ferroelectric is over 5:1. If the diameter or cross section is rectangular, its one side is desirably 20 microns or less. The vol. ratio of the dielectric or ferroelectric to the non-dielectric is pref. 0.3-0.7:1. Thus a damping material having a tan δ of 1 or more and low strain amplitude dependence and no need of the polarizing and electrode fixing steps and hence displays the effect in low-strain factor regions.

Optimum Design of Viscoelastic Layered Beam to Minimize Flexural Vibration

Abstract: For the control of vibration and noise of metal structures having relatively low damping, viscoelastic materials are widely used and usually attached at metal structures with an additional constraining layer to secure them. The damping and elastic properties of structures having constrained viscoelastic material layers are dependent on not only temperature and frequency but also their thicknesses. Hence, optimal design of the thicknesses of viscoelastic and constraining layers for a certain base structure are very important to maximize their efficiency and to lighten their weight. In this study, the variation of loss factor of beams having a constrained viscoelastic layer according to the change of thickness has been carefully investigated. From these, optimal design method of the minimum thickness beam having a given loss factor is suggested and numerically verified for a real beam.

Directional damping material for integrally damped composite plates

Abstract: Current viscoelastic-damping materials behave isotopically so that their stiffness and damping properties are the same in all directions. There is a desire to develop viscoelastic- damping materials that behave orthotropically so that the stiffness and damping properties vary with material orientation. These damping materials can be made othrotropic by embedding rows of thin wires within the viscoelastic damping material. These wires add significant directional stiffness and strength to the damping materials, where the stiffness and strength variation with wire orientation follows classical lamination theory. The presence of these wires introduce different damping mechanisms (longitudinal, transverse, and longitudinal shear damping coefficients) that depend upon mode type and orientation angle. Results from experimental studies show that the magnitude of the loss factor and shear modulus depends upon the mode type and orientation angle of these wires within the damping material. The in-plane axial mode loss factor is highly dependent upon the longitudinal coefficient for (0 degrees) wire orientation, the transverse coefficient for (90 degree) wire orientation, and the longitudinal shear-damping coefficient for all other off-angle wire orientations. The loss factor for the out-of- plane bending and torsion modes is highly dependent upon all three damping coefficients.

Damping component for digital disk driving device

Abstract: PROBLEM TO BE SOLVED: To make sufficiently compensable a deviation due to vibration at the time of digital disk driving by using a thermoplastic resin, which satisfies a specific relation between loss factor and elastic modulus, as a member constituting a component for a digital disk driving device. SOLUTION: A material is selected whose physical properties are such that loss factor multiplied by elastic modulus is larger than 30 MPa, desirably 200 MPa or larger, or more desirably 400 MPa or larger. In this case, if loss factor multiplied by elastic modulus is 30 MPa or less as the physical properties of the material, vibration at the time of disk driving becomes so large that the deviation can no longer be fully compensated by a servo mechanism, causing read errors. A desirable damping component for digital disk driving device can be obtained, which can cope with a large capacity and a high speed of a disk, by using the material satisfying the above conditions.