Showing papers on "Loss factor published in 2022"

Improving the damping properties of carbon fiber reinforced polymer composites by interfacial sliding of oriented multilayer graphene oxide

Abstract: The damping properties of carbon fiber reinforced polymer (CFRP) composites play a critical role in many engineering fields. The purpose of this paper is to investigate how the damping properties of CFRP composites can be improved by interfacial sliding of two-dimensional multilayer graphene oxide (GO). In this work, we show how the energy dissipation ability along the carbon fiber direction is enhanced by oriented GO at carbon fiber/epoxy interface. The damping loss factor of CFRPs is measured by a dynamic mechanical analyzer. The effects of the GO on the damping properties of CFRPs are investigated under different sweep modes (temperature, frequency, and strain). The results show that the deposition of the GO on the surface of the carbon fiber can enhance the damping properties of CFRPs in a wide range of temperature, frequency, and strain domains. Quite significantly, the damping loss factor of CFRPs (0.0345) increases by 113% at a strain of 0.23% and a frequency of 1 Hz. Furthermore, a numerical parametric analysis based on the strain energy method is proposed in ANSYS to obtain the interphase properties of multilayer GO by reference to experimental data. The GO interphase damping parameters can be used to predict the damping properties of multilayer carbon nanomaterials modified composites under different service conditions.

Research and Development of High-Performance High-Damping Rubber Materials for High-Damping Rubber Isolation Bearings: A Review

Abstract: At present, high-damping rubber materials, widely used in the field of engineering seismic isolation, generally have the problems such as narrow effective damping temperature range, low damping loss factor and strong temperature dependence, which lead to prominent dependence of temperature and load conditions of the isolation performance of high-damping rubber isolation bearings. Research and development of high-performance high-damping rubber materials with broad effective damping temperature range, high damping loss factor and weak temperature dependence are very urgent and necessary to ensure the safety of the seismic isolation of engineering structures. This paper mainly reviews the recent progress in the research and development of high-damping rubber materials using nitrile butadiene rubber (NBR), epoxidized natural rubber (ENR), ethylene propylene diene rubber (EPDM), butyl rubber (IIR), chlorinated butyl rubber (CIIR), and bromine butyl rubber (BIIR). This is followed by a review of vulcanization and filler reinforcement systems for the improvement of damping and mechanical properties of high-damping rubber materials. Finally, it further reviews the constitutive models describing the hyperelasticity and viscoelasticity of rubber materials. In view of this focus, four key issues are highlighted for the development of high-performance high-damping rubber materials used for high-damping rubber isolation bearings.

Controllable Design and Preparation of Hydroxyl-Terminated Solution-Polymerized Styrene Butadiene for Polyurethane Elastomers with High-Damping Properties.

Abstract: Vibration and noise are ubiquitous in social life, which severely damage machinery and adversely affect human health. Thus, the development of materials with high-damping performance is of great importance. Rubbers are typically used as damping materials because of their unique viscoelasticity. However, they do not satisfy the requirements of different applications with various working conditions. In this study, the advantages of the high loss factor of styrene butadiene rubber (SBR) are combined with the strong designability of polyurethane. Hydroxyl-terminated solution-polymerized styrene butadiene rubbers (HTSSBRs) with different structures are prepared using anionic polymerization. HTSSBRs are then used as the soft segment during the synthesis of temperature-tunable high-damping performance polyurethane (HTSSBR-polyurethane (PU)). The prepared HTSSBR-PUs with different structures exhibit excellent loss performance, a maximum loss factor (tan δmax ) of above 1.60, and an effective damping performance over a wide temperature range compared to traditional SBR and polyurethane. Therefore, this work offers an effective method for the design of damping materials with adjustable properties. This article is protected by copyright. All rights reserved.

Modified Waveguide-Based Method for Microwave Characterization of High-Loss Materials

Abstract: A waveguide-based measurement configuration is proposed, as a modification to the traditional completely filled waveguide technique, for microwave characterization of relatively thin and high-loss materials. This method is aimed to overcome the large measurement errors caused by gaps and cross-sectional distortions, which are of great concern when measuring high-loss samples, such as unidirectional (UD) carbon-fiber reinforced polymer (CFRP) composite sheets. In this article, the influences of critical parameters, namely, dielectric constant, loss factor, material thickness, and waveguide misalignment, on measured complex permittivity of several diverse samples, are fully investigated through numerical electromagnetic simulations and measurements at $X$ -band (8.2–12.4 GHz). By the virtue of the electromagnetic properties associated with high-loss dielectric materials, it is found that this technique coupled with the Nicolson–Ross–Weir (NRW)/Backer–Jarvis conversion procedure is a capable method for measuring high-loss dielectric materials.

Loss factor and moisture diffusivity property estimation of lentil crop during microwave processing

Abstract: Characterization of loss factor and moisture diffusivity are required to understand materials' precise behavior during microwave processing. However, providing the processing facilities to measure these properties in a real or simulated situation directly can be complicated or unachievable. Hence, this study proposes an alternative procedure for modeling these properties according to their affecting factors including temperature, and moisture content. The basis of this method is to use an algorithm that combines the optimization approach and the numerical solution of the heat and mass transfer governing equations, including boundary conditions. For this aim, the coefficients of estimated models for loss factor and moisture diffusivity were obtained by minimizing the sum square error of the experimentally measured mean surface temperature and moisture content and the predicted values by solving the system of partial differential equations. The suggested models illustrated that during the microwave process, the moisture diffusivity grows arithmetically, and the loss factor generally raises, but transition points were observed in the trend for the samples tempered up to the 50% moisture content. These points have been attributed to the starch gelatinization and confirm how the bio-chemical reaction would have a noticeable effect on this property, determining the microwave energy absorbance. The results of differential scanning calorimetry thermograms and the Fourier transform mid-infrared spectra of flours obtained from microwave processed lentil seeds also confirmed the greatest intensity of starch structure alteration happened for the samples tempered to 50% moisture content by showing the highest shifts in the endothermic peak and lowest degree of order.

Bending and vibration studies of FG porous sandwich beam with viscoelastic boundary conditions: FE approach

Abstract: Abstract Bending and vibration characteristics of FG porous sandwich beam with viscoelastic boundary conditions are investigated. Complex shear modulus and associated loss factor are considered for the viscoelastic interlayer. The beam is constrained by viscoelastic supports (VES) at either end. Complex stiffness model is adopted for VES. The transverse deflection, natural frequency, loss factors, and mode shapes are obtained by varying VES stiffness. Furthermore, the study is extended to sandwich beams with various (H, O, V, and X) porosity patterns. The results convey that VES contribution in vibration damping is more predominant when the supports are less stiff (more viscous).

Determination of Frequency-Dependent Shear Modulus of Viscoelastic Layer via a Constrained Sandwich Beam

Abstract: Viscoelastic material can significantly reduce the vibration energy and radiated noise of a structure, so it is widely used in lightweight sandwich structures. The accurate and efficient determination of the frequency-dependent complex modulus of viscoelastic material is the basis for the correct analysis of the vibro-acoustic behavior of sandwich structures. Based on the behavior of a sandwich beam whose core is a viscoelastic layer, a combined theoretical and experimental study is proposed to characterize the properties of the viscoelastic layer constituting the core. In this method, the viscoelastic layer is bonded between two constraining layers. Then, a genetic algorithm is used to fit the analytical solution of the frequency¬ response function of the free–free constrained beam to the measured result, and then the frequency-dependent complex modulus is estimated for the viscoelastic layer. Moreover, by varying the length of the beams, it is possible to characterize the frequency-dependent complex modulus of the viscoelastic material over a wide frequency range. Finally, the characterized frequency-dependent complex modulus is imported into a finite element model to compute the complex natural frequencies of a sandwich beam, and a comparison of the simulated and measured results displays that the errors in the real parts are within 2.33% and the errors in the imaginary parts are within 3.31%. It is confirmed that the proposed method is feasible, accurate, and reliable. This provides essential technical support for improving the acoustic vibration characteristics of sandwich panels by introducing viscoelastic materials.

Study on the Damping Dynamics Characteristics of a Viscoelastic Damping Material

Abstract: Viscoelastic damping materials are an effective means to control structural vibration, and are widely used in various fields. In this paper, we use the Dynamic Mechanical Analysis (DMA) characterization data of viscoelastic damping materials and dynamic characteristics experiments to study the dynamic characteristics of structural damping, analyze and summarize the relationship between the performance of damping materials with temperature and frequency, and explore the influencing factors of damping materials on structural vibration. The research shows that temperature and frequency have great influence on the performance of damping material, and the storage modulus and loss factor change regularly. The modal experiment analysis verifies that the viscoelastic damping material has a good suppression effect on structural vibration, which provides a theoretical basis for the development of damping materials with controllable temperature and frequency domains.

Design of Load-Bearing Materials for Isolation of Low-Frequency Waterborne Sound

Abstract: Materials with extremely low impedance like air can insulate efficiently waterborne sound, particularly at low frequency, however the poor resistance to load hinders further their applications. This work demonstrates that the elastic anisotropy of materials can not only achieve extremely low impedance, but also high enough stiffness for load bearing. A dimensionless quality factor is proposed to characterize integrately the performance on sound insulation and load bearing of anisotropic materials. It is found that this factor has an upper bound of unity and the corresponding conditions are derived for some particular anisotropic materials. By setting the quality factor to be unity as an objective function for microstructure optimization, a methodology based on topological optimization is proposed to design the microstructure of the corresponding materials with optimized integrated performance on waterborne sound insulation and load bearing. The obtained optimized material is validated by numerical simulation and by comparing with other similar waterborne sound insulation materials with low impedance. This study paves the way for designing load-bearing materials with extremely low impedance, and opens a route to control low-frequency underwater waves.

A study on the conductivity, dielectric, and microwave properties of (SrNbxYxFe12-2xO19 (0.00 ≤ x ≤ 0.05) nanohexaferrites

Abstract: In this paper, conductivity, dielectric, and microwave properties of SrNbxYxFe12-2xO19 (0.00 ≤ x ≤ 0.05) hexaferrites (SrNbY HFs) synthesized by the citrate sol–gel method were investigated. Some key parameters compatible with the electrical and dielectric functions of SrNbY HFs have been extensively evaluated as functions of bias frequency, measurement temperature, and co-substitution ratios in logarithmic 3D graphs by complex impedance spectroscopy. It has been observed that although the co-substitution ratio is highly functional on dielectric parameters such as both the dielectric constant and dielectric loss, as well as the dissipation factor, it has a very low influence on the conductivity mechanism. Depending on the substitution ratios of Nb and Y ions and the transition temperature region, the activation energy was calculated to vary between 58 and 476 meV. Microwave properties were measured as S-parameters using a coaxial line in the range of 2–12 GHz. It was analysed the frequency dependences of the real/imaginary parts of the permittivity and permeability for all samples. Reflection losses vs. frequency were calculated as a function of the substitution level. Coefficients of the RL (−12.5 … −16.8 dB) confirm practical importance for electromagnetic compatibility at high frequencies.

Temperature and Moisture Dependent Dielectric and Thermal Properties of Walnut Components Associated with Radio Frequency and Microwave Pasteurization

Abstract: To provide necessary information for further pasteurization experiments and computer simulations based on radio frequency (RF) and microwave (MW) energy, dielectric and thermal properties of walnut components were measured at frequencies between 10 and 3000 MHz, temperatures between 20 and 80 °C, and moisture contents of whole walnuts between 8.04% and 20.01% on a dry basis (d.b.). Results demonstrated that dielectric constants and loss factors of walnut kernels and shells decreased dramatically with raised frequency within the RF range from 10 to 300 MHz, but then reduced slightly within the MW range from 300 to 3000 MHz. Dielectric constant, loss factor, specific heat capacity, and thermal conductivity increased with raised temperature and moisture content. Dielectric loss factors of kernels were greater than those of shells, leading to a higher RF or MW heating rate. Penetration depth of electromagnetic waves in walnut components was found to be greater at lower frequencies, temperatures, and moisture contents. The established regression models with experimental results could predict both dielectric and thermal properties with large coefficients of determination (R2 > 0.966). Therefore, this study offered essential data and effective guidance in developing and optimizing RF and MW pasteurization techniques for walnuts using both experiments and mathematical simulations.

Experimental Investigation of Friction Damping in Blade Root Joints

Abstract: The design of disk assemblies requires the capability to predict their dynamic behavior. To achieve this objective, knowledge of friction damping on the contact between blade and disk is of paramount importance. This paper proposes an experimental technique to measure the loss factor and the dynamics, in terms of natural frequencies, of blade-disk attachment. The free decay is used to infer the dynamic parameters from dummy blades. The identification method is based on the Hilbert transform that al-lows extracting the dynamic parameters from non-linear system. This paper shows the test rig utilized in the experimental analysis and details the excitation system used to displace the dummy blade. This system must be a real or a "virtual" non-contact system to avoid injecting external damping into the blade under test. Tests were performed on both a dovetail and a fir-tree type attachments. On the dovetail, tests were performed both with dry contact surfaces and with contact surfaces covered by a film of lubricant to achieve a low coefficient of friction. This low coefficient of friction better simulates dry surfaces at high temperatures, as friction coefficients decrease with temperatures. This paper presents the results obtained on the first and second bending mode. The experimental results show the loss factor and the natural frequency for different axial loads. The measured loss factor depends on the amplitude of vibrations. The loss factor shows a maximum then approaching zero for large amplitude of vibrations and it decreases with increasing centrifugal loads.

An Experimental Approach for the Determination of the Mechanical Properties of Base-Excited Polymeric Specimens at Higher Frequency Modes

Abstract: Structures made of the thermoplastic polymer polyether ether ketone (PEEK) are widely used in dynamically-loaded applications due to their high-temperature resistance and high mechanical properties. To design these dynamic applications, in addition to the well-known stiffness and strength properties the vibration-damping properties at the given frequencies are required. Depending on the application, frequencies from a few hertz to the ultrasonic range are of interest here. To characterize the frequency-dependent behavior, an experimental approach was chosen and applied to a sample polymer PEEK. The test setup consists of a piezoelectrically driven base excitation of the polymeric specimen and the non-contact measurement of the velocity as well as the surface temperature. The beam’s bending vibrations were analyzed by means of the Timoshenko theory to determine the polymer’s storage modulus. The mechanical loss factor was calculated using the half-power bandwidth method. For PEEK and a considered frequency range of 1 kHz to 16 kHz, a storage modulus between 3.9 GPa and 4.2 GPa and a loss factor between 9 × 10−3 and 17 × 10−3 were determined. For the used experimental parameters, the resulting mechanical properties were not essentially influenced by the amplitude of excitation, the duration of excitation, or thermal degrad.ation due to self-heating, but rather slightly by the clamping force within the fixation area.

Preparation and characterization of natural rubber–based new elastomers for high-damping base isolation systems

Abstract: Natural rubber (NR)–based vulcanizates have been used as base isolation materials for many years. Combining good damping properties, low cost, and availability with acceptable mechanical and aging performance, these materials have always been the first choice for base isolation applications. In this research, we try to formulate a natural rubber base recipe with increased damping properties, which can fulfill mechanical and aging requirements of base isolation systems. For this purpose, a series of blends have been formulated by incorporating chloroprene (CR) or butadiene (BR) and acrylonitrile butadiene rubber (NBR) into the natural rubber base. Filler content accelerator type and vulcanization system have been chosen to optimize damping while maintaining a reference point. All vulcanizates have been tested for their mechanical properties. Moving die rheometer (MDR) and rubber process analyzer (RPA) have been used to obtain general cure data as well as storage (G′) and loss modulus and loss angle (η). Crosslink densities have been calculated using RPA and Lee and Pawlowsky’s Coran approach. Dynamic material tests have been performed to obtain dynamic shear properties, equivalent damping ratio, and shear modulus. The results indicated that NR/NBR and NR/CR compounds with viscous damping values of 10.4% and 8.9% at frequency of .5 Hz can lay bases for formulating high-damping rubber (HDR) materials for base isolation systems due to their increased damping and rather good mechanical and relaxation performance.

Evaluation of Relative Permittivity and Loss Factor of 3D Printing Materials for Use in RF Electronic Applications

Abstract: 3D printing is more and more often used for the development and manufacturing of electronic devices and components. These applications require knowledge about the dielectric properties of the used materials—in particular minimal and stable values of relative permittivity and dielectric losses. The paper deals with the testing of the relative permittivity and loss factor of materials as follows: PLA (in three dye modifications), PET-G, and ABS and ASA in the frequency range 1–100 MHz. It was found that relative permittivity varied between 2.88–3.48 and the loss factor was in the range 0.03–4.31%. In terms of relative permittivity, all tested materials manifested a slight decline with increasing frequency. Concerning loss factor PLA (colorless) and ABS were proven to be more suitable for electrotechnical application due to the lower values and frequency dependences of the loss factor. Different results were observed in PLA-Silver and PLA-Metallic green. These materials showed a higher frequency dependency of loss factor with increasing frequency. The reasonable influence of added dyes was found. A study of the internal structure of the tested materials has not proven any significant defects (air gaps) that could affect the material’s dielectric properties.

The Dielectric Properties of Worker Bee Homogenate in a High Frequency Electric Field

Abstract: Biological tissues, including insect tissues, are among lossy dielectric materials. The permittivity properties of these materials are described by loss factor ε″ and loss tangent tgδ. The dielectric properties of the worker honeybee body homogenate are tested in the range of high frequencies from 1 MHz to 6 GHz. The homogenate is produced by mixing whole worker honeybees and tested with an epsilometer from Compass Technology and a Copper Mountain Technologies vector circuit analyser VNA. Due to their consistency, the homogenate samples are placed inside polyurethane sachets. The measured permittivity relates to two components of a sample: homogenate and polyurethane. For five samples, two extremes were specified for the permittivity, loss factor ε″, and the loss tangent tgδ, for the frequency range 20 ÷ 80 MHz and 3 GHz. Four techniques of testing permittivity in biological tissues were used to determine the dielectric properties of the homogenate. A calculation model was developed featuring a minimum measurement error of the loss factor ε″ and the loss tangent tgδ. The power absorbed per unit volume is described for the whole frequency range.

Characterization of Low-Loss Dielectric Materials for High-Speed and High-Frequency Applications

Abstract: In this study, the Df (dissipation factor) and Dk (dielectric constant) of the low loss dielectric material from three different Vendors are characterized by the Fabry-Perot open resonator (FPOR). Emphasis is placed on the sample preparation, data collection, and the comparison with the data sheet values provided from Vendors. A coplanar waveguide with ground (CPWG) test vehicle with one of these Vendors is being designed (through Polar and simulation) and fabricated. The impedance of the test vehicle is measured by TDR (time-domain reflectometer) and the effective Dk of the test vehicle is calculated by the real cross section of the test vehicle and a closed-form equation. In parallel, the insertion loss and return loss are measured with the VNA (vector network analyzer) of the test vehicle. Finally, the measurement and simulation results are correlated. Some recommendations on the low loss dielectric materials of the Df and Dk are also provided.

Dynamic mechanical analysis of continuous carbon fiber‐reinforced polyetheretherketones under multi‐consecutive temperature scans

Abstract: The study analyzed the dynamics mechanical properties of carbon fiber-reinforced polyetheretherketone (CF/PEEK) under multi-consecutive temperature scans and establish an evaluation model of storage modulus to facilitate application in high/low temperature. The dynamic mechanical properties of CF/PEEK laminate sheets obtained via hot-pressing procedure were subjected to a dynamic mechanical cycle test. The micromorphology and microstructure were observed with a scanning electron microscopy. The structural evolution of CF/PEEK and the interface between carbon fiber and PEEK matrix were analyzed. The characteristic variation of storage modulus, loss modulus, and loss factor are discussed and the damping properties are studied in different temperature ranges. The results show that the dynamic mechanical properties of CF/PEEK were become stabilized after the first temperature scan, while the glass transition temperature remained basically unchanged. The storage modulus of the material increased by 15.8% and the peak value of the loss factor curve increased by 14.4%. Based on the experimental data, an evaluation model of the storage modulus was formulated and validated by the test results obtained to provide an accurately predicting the dynamic mechanical properties of CF/PEEK and expand its engineering applications.

Dielectric loss mechanism of powdered infant formula milk

Abstract: Dipole loss of main compositions of powdered infant formula milk (PIFM), including whey protein (WP), fat and lactose and the ionic loss of PIFM were analyzed over frequency range of 10 to 3000 MHz at temperature range of 20–80 °C. Dielectric loss factor of PIFM decreased with increasing fat content, while increased with increasing WP content and lactose content at investigated frequencies in our study. The dipole loss of WP, fat and lactose followed Debye equation which increased with increasing frequency till around 1.2,1 and 1 GHz, respectively, and then decreased. Ionic loss of PIFM was constant with increasing frequency at investigated frequencies and increased with increasing temperature. A general formula to calculate ionic loss for both solid and liquid materials was obtained. Validation experiments based on the dielectric loss factor of different compositions indicated that increasing WP proportion in PIFM can increase heating rate in radio frequency field and also result in lower lipid oxidation of treated PIFM. This provides a solution to adjust RF heating performance and product quality based on loss mechanisms of different ingredients.

Free vibration analysis of a porous functionally graded, truncated conical shell with a magneto-rheological fluid core

Abstract: Vibration absorbers are vital to resisting shocks in many structures. This study analyzed the effects of magnetic field, porosity and geometry on the natural frequency and loss factor of a conical shell made of smart porous materials. Natural frequency declined when the length, radius and thickness ratios increased. The loss factor and porosity coefficients increased concurrently. The magnetic intensity had little effect on the natural frequency. Increasing the apex angle or porosity, raised the loss factor but reduced the natural frequency. Raising the core’s top layer thickness reduced the natural frequency but increasing the L/R1 or R1/h ratio reduced the frequency.

Comparison of Dynamic Performance of an All-Metallic Vibration Isolator by Elliptic Method and Frequency Sweeping Method

Abstract: A horizontally symmetric all-metallic vibration isolator (AM-VI) is proposed to further investigate the dynamic mechanical performance. The novel AM-VI was constructed by combining hat-shaped metal rubber and oblique springs, which were connected in parallel. The springs were arranged symmetrically relative to the support. The elliptic method and the frequency sweeping method were used to compare the dynamic stiffness and the loss factor of the AM-VI. The results demonstrated that the dynamic stiffness and the loss factor calculated by two distinct test methodologies were considerably different, indicating that the inertial force effect of the dynamic testing equipment should be taken into count when adopting the elliptic method. Furthermore, when the vibration isolation performance was evaluated by utilizing mechanical impedance and force transmissibility, the AM-VI achieved excellent vibration isolation performance within a broad frequency range.

Determination of the dynamic performance of natural viscoelastic composites with different proportions of reinforcing fibers

Abstract: Abstract Viscoelastic composites are strong and handle vibration damping quite well, which allows them to be used in a wide variety of applications. Thus, there is a need to determine the optimal amount of fiber to ensure high mechanical and dynamic performance with as little interference as possible. The purpose of this work is to find the most appropriate percentage of organic fiber – cellulose derived from corn stalks in a polylactic acid matrix, studying the changes in damping characteristics, tensile strength, bend-test. As parameters for comparison, the coefficient of bending and breaking strength, modules of accumulation and losses, factor C were chosen. It was found that strength indicators decrease with fiber fraction growth. While the damping factor at the glass transition temperature increases. In order to confirm the results obtained, the calculation of the C factor was used. The study investigates the damping factor’s dependence on the mechanical properties. It is shown that there is a correlation between moduli and bending strength with increasing fiber fraction. The scientific novelty of this work is the study of natural viscoelastic composites with different proportions of reinforcing fibers based on mechanical and dynamic characteristics in order to create and apply biodegradable viscoelastic composites in various fields.