Showing papers on "Loss factor published in 2006"

Foil Gas Bearing With Compression Springs: Analyses and Experiments

Abstract: A new foil gas bearing with spring bumps was constructed, analyzed, and tested. The new foil gas bearing uses a series of compression springs as compliant underlying structures instead of corrugated bump foils. Experiments on the stiffness of the spring bumps show an excellent agreement with an analytical model developed for the spring bumps. Load capacity, structural stiffness, and equivalent viscous damping (and structural loss factor) were measured to demonstrate the feasibility of the new foil bearing. Orbit and coast-down simulations using the calculated stiffness and measured structural loss factor indicate that the damping of underlying structure can suppress the maximum peak at the critical speed very effectively but not the onset of hydrodynamic rotor-bearing instability. However, the damping plays an important role in suppressing the subsynchronous vibrations under limit cycles. The observation is believed to be true with any air foil bearings with different types of elastic foundations.

Electrical conduction and dielectric relaxation in semiconductor SeSm0.005

Abstract: The dc and ac conductivity of polycrystalline SeSm0.005 bulk samples have been measured under vacuum in the temperature range 363–93 K. The samples displayed dielectric dispersion in the frequency range 50 Hz–80 kHz. The calculated values of the exponent s of the function σ = Aωs showed that correlated barrier hopping is the suitable model to describe the ac conduction mechanism. Calculation of the real dielectric constant (e'), loss factor (e'') and loss tangent (tan δ) are given in the studied frequency and temperature ranges. The loss factor displayed a loss peak that gives direct evidence of the existence of a Debye relaxation type. Also, the arc shape of Cole–Cole diagrams has been used to determine and discuss the optical (e∞) and static (es) dielectric constants besides the macroscopic relaxation (τ0) and molecular relaxation (τ) times.

Measurement of the resonance frequency, the loss factor, and the dynamic Young's modulus in structural steel and polycarbonate by using an acoustic velocity sensor

Abstract: An acoustic velocity sensor, micro-flown, was used to monitor the vibration signal in measurements of the resonance frequency, the loss factor, and the dynamic Young’s modulus of structural steel and polycarbonate by using a resonance method. The results showed that the measured loss factors of the structural steel and polycarbonate used in the present specimen were 0.0023 and 0.056, respectively, and the Young’s moduli were 198.4 GPa and 2.4 GPa. The values measured with micro-flown agreed with those obtained with a conventional displacement sensor and with the theoretically estimated and reference values. The agreements ensure the reliability of the use of a micro-flown acoustic velocity sensor in measuring the resonance frequency, the loss factor, and the dynamic Young’s modulus.

Numerical parametric investigation of loss factor of laminated composites with interleaved viscoelastic layers

Abstract: In this paper a detailed parametric study of loss factor of laminated composite beams with embedded viscoelastic layers has been performed using the finite-element-based modal strain energy method revised to deal with the frequency dependency of viscoelastic materials. The contribution of energy dissipation due to fiber-reinforced composites is also taken into account for a more accurate prediction of loss factor. The effects of different parameters such as ply orientations, location of damping layers and thickness of the laminates on the modal loss factor are investigated for both single damping layer and double damping layer composite beams.

Influence of Viscosity Loss on Coupled Vibrations of Ultrahigh Frequency AT-Cut Quartz Plates

Abstract: We numerically analyze the influence of viscosity loss in quartz on the unwanted coupling between fundamental thickness-shear (TS) and spurious modes. Classical mode-matching is used to solve the two-dimensional coupled vibrations in an AT-cut quartz plate with an inverted-mesa shape. Using this technique, we calculate the loci of admittance near the main TS response as a function of the loss factor. The temperature behavior of frequency and conductance is also examined for the main TS resonance. The results reveal that, for two strongly coupled vibrations of TS and spurious modes, two resonances on the real frequency-axis are combined into one with increasing loss, although there are still two resonances in the complex frequency plane. We also find that the conductance–temperature behavior of the main TS response is more sensitive to mode coupling than the frequency–temperature behavior, and it therefore works well as a detector of mode coupling.

Vibrational Damping of Composite Materials

Abstract: The purpose of this research was to develop new methods of vibrational damping in polymeric composite materials along with expanding the knowledge of currently used vibrational damping methods. A new barrier layer technique that dramatically increased damping in viscoelastic damping materials that interacted with the composite resin was created. A method for testing the shear strength of damping materials cocured in composites was developed. Directional damping materials, where the loss factor and modulus could be tailored by changing the angle, were produced and investigated. The addition of particles between composite prepreg layers to increase damping was studied. Electroviscoelastic materials that drastically changed properties such as loss factor and modulus with an applied voltage were manufactured and tested

Analysis of damping characteristics of a viscoelastic polymer filled with randomly oriented single-wall nanotube ropes

Abstract: This paper presents an analysis on the structural damping characteristics of polymeric composites containing dilute, randomly oriented nanoropes. The SWNT (single-wall nanotube) rope is modeled as a closed-packed lattice consisting of seven nanotubes in hexagonal array. The resin is described as a viscoelastic material using two models: Maxwell model and three-element standard solid model. The composite is modeled as a three-phase system consisting of a resin, a resin sheath acting as a shear transfer zone, and SWNT ropes. The "stick-slip" mechanism is proposed to describe the load transfer behavior between a nanorope and a sheath and between individual SWNTs. The analytical results indicate that the loss factor of the composite is sensitive to stress magnitude. It is illustrated that the "stick-slip" friction is the main contribution for the total loss factor of CNT-based composites even with a small amount of nanotubes/ropes.

Tire for e.g. private vehicle, has self sealing layer with loss factor and dynamic modulus lower than inflation pressure, where loss factor and dynamic modulus are measured at ten hertz frequency, and layer covers portion of internal wall

Abstract: The tire (1) has a crown (2) provided radially outside of a tire tread (8), and two sidewalls (3), whose internal surface and the crown forming an internal wall of the tire. A portion of the wall is covered by a self sealing layer (11) made up of styrene thermoplastic elastomer. The self sealing layer has a loss factor lower than the 0.2, and a dynamic modulus lower than the inflation pressure of the tire, for temperature ranging between 30 and 100 degree Celsius. The loss factor and dynamic modulus are measured at the 10 hertz frequency.

Methods of analyzing the vibro-acoustic optimization potential and optimizing the vibro-acoustic behavior of a structure

Abstract: The invention relates to a method of analyzing the vibro-acoustic optimization potential of a structure of vibro-acoustically coupled subsystems having internal and coupling loss factors by means of statistical energy analysis (SEA). The invention further relates to a method of optimizing the vibro-acoustic behavior of such a structure. The inventive methods involve the steps of: calculating the gradient of energy on the basis of a simplified SEA matrix in which all coupling loss factors θji with j>i have been substituted according to η ij n i =η ji n j ; identifying the internal loss factors causing the M highest gradients as dominant internal loss factors and the coupling loss factors causing the N highest products, which each consist of a gradient times its coupling loss factor, as dominant coupling loss factors; calculating an optimization potential for each of the dominant internal and coupling loss factors as the maximum sub-system energy change which can be achieved by varying said loss factor; and identifying the dominant internal and coupling loss factors with the K highest optimization potentials as optimization loss factors for the further vibro-acoustic optimization of the structure.

Experimental studies on the loss factor of alternately laminated anisotropic damped thin plates

Abstract: Optimization designs on the parameters of seven-layers of alternately laminated thin plate structures have been carried out through two orthogonal experiments and a dynamic mechanical analysis apparatus (DMA Q800), including the variations of damping material species, the fiber orientation angle in constrained layers and the thickness of the damping layer. The effects of these parameters on the loss factor of the structures have been investigated. It may provide some experimental basis for new anisotropic design system of the alternately laminated damped structures. Firstly, the experimental results show that the second and the sixth damping layers are respectively the best-influencing layers on the frequency range and the temperature range of the loss factor. As for the second damping layer, the greater the thickness, the better the frequency characteristics of internal friction. Secondly, the effects of the second outer constrained layer on the loss factor are the highest, and the structural damping cha...

Sea 기법을 이용한 저중량 흡, 차음재의 대시판넬 적용에 대한 연구

Abstract: In this Paper Statistical Energy Analysis has been considered to predict high frequency air borne interior noise. Insulation thickness distribution map was calculated not by measurement, but by FeGate software. AutoSEA software predicted coupling loss factor from insertion loss which was measured by using Reiter Apamat Ⅱ machine and internal damping loss factor from reverberation time according to each thickness and material density. Each predicted transmission losses between conventional insulation and light weight insulation are compared with SEA. Finally light weigh insulation system has lower sound transmission loss and higher absorption coefficient than conventional system.

Comparative Study of Aluminum Alloy Plate 2024/7050 Under the Effect of Internal Damping

Abstract: In the present work we determine the influence of structural damping, of an aluminum alloy on the dynamic behavior of a plate with various boundary conditions Structural damping (loss factor energy) is a very significant parameter by its influence on the dynamic behavior of the mechanical structures The material of the studied plate is the aluminum alloy 2024 T3 and 7050 T7351 The behavior vibratory of the plate is studied by the finite element method and a comparative study is presented for theses materials We present also the influence of the loss factor energy on the variation of the inertance relating to each node and each degree of freedom In parallel, we study the influence of the geometrical parameters of the structure in the frequency domain In addition, we identify the excited mode of vibration where a comparative example for steel is presented in order to show the excited mode of vibration The effect of the internal damping is significant in resonance peak, where the reduction of the vibratory amplitude (inertance) is significant The increase of the geometrical parameters (thickness, ratio length/width), decreases the vibratory amplitude, and on the other hand shift the peaks of resonance towards the high frequencies The boundary conditions have a great influence on the rotational inertances in a resonance peak