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Indium-zinc in situ composites were fabricated and their viscoelastic properties studied over 8.5 decades of frequency. Material with 5% indium by weight was found to have a stiffness damping product (the figure of merit for damping layers) of 1.9 GPa at 10 Hz; 3 times better than the peak of polymer damping layers and over a wider frequency range. Material with 15% indium had a stiffness damping product of 1.8 GPa. The indium segregated in a platelet morphology, particularly favorable for attaining high damping from a small concentration, as predicted by viscoelastic composite theory.

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... A common measure to reduce the vibrations of a structure is to place damping material in the connections between its components. As most metals provide only poor damping performance if the deformations are small [1], polymers with high loss factors like polyurethane elastomers are often employed for this purpose. Their relatively small stiffness, however, can lead to even larger vibrations in directly excited components [2]. ...

... Metals with good damping properties at small strains were studied in [1,[3][4][5][6][7]. For example, cadmium showed a shear modulus of 20.7 GPa and a frequency-dependent loss factor from 0.05 to 0.03 in the range of 1 Hz to 1000 Hz [3]. ...

... Nevertheless, apart from other constraints, it should be considered that heavy metals such as cadmium can have a negative impact on human health, which limits their application in building products [8]. High stiffness and damping values were also measured from samples of indium-tin [5], indium-zinc [1], as well as composites combining indium-tin with tungsten [4] or silicon carbide [6] to increase stiffness. ...

Metal lattice structures filled with a damping material such as polymer can exhibit high stiffness and good damping properties. Mechanical simulations of parts made from these composites can however require a large modeling and computational effort because relevant features such as complex geometries need to be represented on multiple scales. The finite cell method (FCM) and numerical homogenization are potential remedies for this problem. Moreover, if the microstructures are placed in between the components of assemblies for vibration reduction, a modified mortar technique can further increase the efficiency of the complete simulation process. With this method, it is possible to discretize the components separately and to integrate the viscoelastic behavior of the composite damping layer into their weak coupling. This paper provides a multiscale computational material design framework for such layers, based on FCM and the modified mortar technique. Its efficiency even in the case of complex microstructures is demonstrated in numerical studies. Therein, computational homogenization is first performed on various microstructures before the resulting effective material parameters are used in larger-scale simulation models to investigate their effect and to verify the employed methods.

... scoelastic parameters and time dependence of creep stiffness modulus can be obtained from the simulation of the experimental data. The result shows that creep stiffness modulus decreases rapidly at the initial stage of loading, then the rate of change decreases, and finally creep stiffness modulus approaches to a stable value at the end of loading.Balch, Lakes (2015). Indium-zinc in situ composites were fabricated and their viscoelastic properties studied over 8.5 decades of frequency. Material with 5% indium by weight was found to have a stiffness damping product (the figure of merit for damping layers) of 1.9 GPa at 10 Hz; 3 times better than the peak of polymer damping layers and over a wider fre ...

Visco-elastic dampers utilize high damping from Viscoelastic materials to dissipate energy through shear deformation. Viscoelastic materials are highly influenced by parameters like temperature, frequency, dynamic strain rate, time effects such as creep and relaxation, aging, and other irreversible effects. Hence selecting a proper viscoelastic material is the key. This paper presents an overview of literature related to the viscoelastic materials used in visco elastic dampers. The review includes different materials like asphalt, rubber, polymer and glassy substances. There have been few investigations on these materials, its advantages and disadvantages are discussed and detailed review is carried out.

Through a combination of a molecular dynamics (MD) simulation and experimental method, in this work we have methodically expatiated the essential mechanism of the observably enhanced damping performance of nitrile-butadiene rubber (NBR) ascribed to the introduction of hindered phenol AO-70. The computed results revealed that four types of hydrogen bonds (H-bonds), namely, type A (AO-70) -OH?NC- (NBR), type B (AO-70) -OH?OC- (AO-70), and type C (AO-70) -OH?OH- (AO-70), type D (AO-70) -OH?O-C- (AO-70) were formed in the AO-70/NBR composites, where type A was the most stable. Meanwhile, the AO-70/NBR composite with AO-70 content of 109 phr had the largest number of H-bonds, highest binding energy, and smallest fractional free volume (FFV), demonstrating a good compatibility between NBR and AO-70 and the best damping property of the composites. The experimental results were highly consistent with the MD simulation results, which means the combining methods can provide a new attempt for the design of optimum damping materials.

High viscoelastic damping is observed in InZn materials over ranges of composition, frequency, temperature, and annealing time. Microscopy reveals InZn when cast segregates into a heterogeneous micro-structure resembling an in situ composite consisting of a zinc matrix with soft indium platelet inclusions. This morphology is predicted to be advantageous for maximizing the damping figure of merit Etanδ by viscoelastic composite theory. InZn is found to be linearly viscoelastic, unlike other high damping metals. The damping of InZn varies little over a substantial range of temperature, in contrast with polymers. For 5 % In material, the optimal composition, Etanδ is 2.8 GPa at 10 Hz, compared to a peak of 0.6 GPa for high damping rubbers. After annealing for 13 years, Etanδ was still high at 1.9 GPa. InZn demonstrates high damping under a wide range of conditions.

Material damping of laminated composites is experimentally determined by the half-power bandwidth method for cantilever beam specimens excited with an impulse excitation. Data acquisition and manipulation are carried out using both an IBM PC-AT and a GenRad 2500 Series FFT Analyzer. Unidirectional continuous fiber 0° and 90° laminates were fabricated from glass/epoxy (Hercules S2-Glass/3501-6), graphite/epoxy (Hercules AS4/3501-6) and graphite/poly (ether ether ketone) (ICI AS4/PEEK[APC-2]) to investigate the effect of fiber and matrix properties as a function of frequency, up to 1000 Hz, on the damping of composites. The S2-glass/3501-6 composite had a higher loss factor than the AS4/3501-6 in the 0° orientation with the loss factor for the AS4/3501-6 exhibiting a linear increase with increasing frequency and the loss factor for the S2-glass varying nonlinearly with frequency. The 90° material exhibited a higher damping loss factor than the 0°, varying nonlinearly with increasing frequency. In the 90° orientation, the glass fiber composite had loss factors that were approximately fourfold greater than the 0° orientation at frequencies greater than 200 Hz. The 0° AS4/PEEK had a loss factor that was approximately equal to that of the 0° AS4/3501-6. The 90° AS4/PEEK had a loss factor that was approximately 50% less than the AS4/3501-6 and 25% greater than the S2-glass/3501-6 composite.

Metal matrix composites of silicon carbide particles in indium–tin alloy were fabricated with the aim of achieving a high value of the product of stiffness and viscoelastic damping tan , without excess density. Stiffness and viscoelastic damping were measured over a wide range of frequency. For monodisperse 40% by volume SiC, and for hierarchical 60% by volume SiC the composite damping increased compared with the matrix at frequencies above 100 Hz. Composite shear modulus was almost a factor two greater than matrix for 40% and a factor of four greater than that of matrix for 60%. The product of stiffness and damping exceeds that of well-known materials including polymer damping layers. Hashin–Shtrikman analysis modelled the observed stiffness increase. The damping increase at higher frequency cannot be accounted for by a purely mechanical composite model; it is attributed to thermoelastic coupling and an increase in matrix dislocations during fabrication.

Characterization of the mechanical damping properties of a series of die-cast zinc-aluminum alloys is described. Over the
range of variables (temperature, frequency, and vibration strain amplitude) normally encountered in service applications,
it is shown that the damping consists of two components. Both components are due to linear relaxation mechanisms: the first
is a thermoelastic relaxation and the second is the low-temperature tail of a broadened boundary relaxation. Some of the alloys
exhibit elevated damping levels over a useful frequency range, particularly at the temperatures encountered in under-hood
applications in automobiles.

A theoretical study of the viscoelastic properties of composites is presented with the aim of identifying structures which give rise to a combination of high stiffness and high loss tangent. Laminates with Voigt and Reuss structures, as well as composite materials attaining the Hashin-Shtrickman bounds on stiffness were evaluated by the correspondence principle. Similarly, viscoelastic properties of composites containing spherical or platelet inclusions were explored. Reuss laminates and platelet-filled materials composed of a stiff, low-loss phase and a compliant high-loss phase were found to exhibit high stiffness combined with a high loss tangent.

This article compares resonant ultrasound spectroscopy (RUS) and other resonant methods for the determination of viscoelastic properties such as damping. RUS scans from 50 to 500 kHz were conducted on cubical specimens of several materials including brass, aluminum alloys, and polymethyl (methacrylate) (PMMA), a glassy polymer. Comparison of damping over the frequency ranges for broadband viscoelastic spectroscopy (BVS) and RUS for indium tin alloy in shear modes of deformation discloses a continuation of the tan δ power-law trend for ultrasonic frequencies up to 300 kHz. For PMMA, resonant peaks were sufficiently broad that higher modes in RUS began to overlap. Tan δ via RUS and BVS for PMMA agreed well in the frequency range where the methods overlap. RUS is capable of measuring tan δ as high as several percent at the fundamental frequency. Since higher modes are closely spaced, it is impractical to determine tan δ above 0.01-0.02 at frequencies other than the fundamental.

Viscoelastic materials are widely used for acoustic attenuation, isolation of continuous vibration, and shock mountings. The properties of these materials are dependent upon temperature and frequency of excitation, molecular structure of the base polymer, and chemical cross-linking systems and fillers. This paper describes a transfer function technique for the measurement of the frequency-dependent Young's modulus and loss tangent. Algorithms for time-temperature superposition are also discussed. It is then shown how the results of such measurements can be used in the selection of viscoelastic materials and fillers in the design of constrained-layer damping structures. Comparisons of mathematical modeling and experimentally determined damping are given for some of the chlorobutyl formulations discussed.

Understanding viscoelasticity is pertinent to design applications as diverse as earplugs, gaskets, computer disks, satellite stability, medical diagnosis, injury prevention, vibration abatement, tire performance, sports, spacecraft explosions, and music. This book fits a one-semester graduate course on the properties, analysis, and uses of viscoelastic materials. Those familiar with the author's precursor book, Viscoelastic Solids, will see that this book contains many updates and expanded coverage of the materials science, causes of viscoelastic behavior, properties of materials of biological origin, and applications of viscoelastic materials. The theoretical presentation includes both transient and dynamic aspects, with emphasis on linear viscoelasticity to develop physical insight. Methods for the solution of stress analysis problems are developed and illustrated. Experimental methods for characterization of viscoelastic materials are explored in detail. Viscoelastic phenomena are described for a wide variety of materials, including viscoelastic composite materials. Applications of viscoelasticity and viscoelastic materials are illustrated with case studies.

Composite micro-structures are studied, which give rise to high stiffness combined with high viscoelastic loss. We demonstrate that such properties are most easily achieved if the stiff phase is as stiff as possible. Incorporation of a small amount of damping in the stiff phase has little effect on the composite damping. Experimental results are presented for laminates consisting of cadmium and tungsten and of InSn alloy and tungsten. The combination of stiffness and loss (the product E tan &dgr;) exceeds that of well-known materials.

The effective moduli of platelet reinforced media are derived for aligned and randomly oriented circular platelets at both dilute and finite concentrations. The platelets are modeled as very thin oblate spheroids in which edge effects caused by the presence of the sharp corners can be significant, depending upon the relative magnitudes of the thickness-to-diameter ratio and the ratio of the matrix stiffness to that of the reinforcer. The edge effects become negligible when the latter ratio greatly exceeds the former, in which case the platelets act effectively as infinite layers. In general, the non-uniform stress fields in the vicinity of the sharp corners or edges cause a reduction in the effective moduli. When the aspect ratio greatly exceeds the stiffness ratio, the inclusions become equivalent to rigid disks, and the pertinent concentration parameter is not the volume fraction, which is zero, but a number analogous to the crack density parameter for solids containing cracks. Effective medium theories for finite concentrations of rigid disks predict that the effective Poisson's ratio tends to the value 0.1557… as the concentration increases, and the self-consistent theory displays a critical disk density at which the composite becomes rigid.

The figure of merit for structural damping and damping layer applications is the product of stiffness E and damping tan δ. For most materials, even practical polymer damping layers, E tan δ is less than 0.6 GPa. We consider several methods to achieve high values of this figure of merit: high damping metals, metal matrix composites and composites containing constituents of negative stiffness. As for high damping metals, damping of polycrystalline zinc was determined and compared with InSn studied earlier. Damping of Zn is less dependent on frequency than that of InSn, so Zn is superior at high frequency. High damping and large stiffness anomalies are possible in viscoelastic composites with inclusions of negative stiffness. Negative stiffness entails a reversal of the usual directional relationship between force and displacement in deformed objects. An isolated object with negative stiffness is unstable, but an inclusion embedded in a composite matrix can be stabilized under some circumstances. Ferroelastic domains in the vicinity of a phase transition can exhibit a region of negative stiffness. Metal matrix composites containing vanadium dioxide were prepared and studied. The concentration of embedded particles was sensitive to the processing method.

The β-type Ti alloys with high oxygen solid solution was developed as a new type of high-damping alloy, in which oxygen could cause both a strengthening effect for higher strength and a huge Snoek damping peak. Snoek damping mechanism was applied to Ti-Nb-O alloys, and the high damping capacity and high strength induced by a certain amount of oxygen solid solution in the alloys were much better than those obtained in already developed high damping alloys. A strengthening effect was observed in the Ti-25Nb-1.5 O alloy with the 1.7% oxygen solid solution, in which the yield strength was increased to 665.3 MPa with a decrease of elongation to 17.1%. When the oxygen composition was increased to 3.0%, the as-cast alloy ingot ruptured during the elastic deformation stage, which was caused by the microcracks formed in the ingot during the rapid solidification process in the cold crucible.

Internal friction and elastic moduli of the intermetallic compound TiNi were measured as a function of temperature from -170° to 800°C. There appear in the internal friction curve two well‐defined peaks at -70° and 600°C, respectively, a small peak at 350°C, and a group of several sharp peaks in the temperature range from -50° to 40°C. The elastic modulus has a positive temperature coefficient in the temperature range from 40° to 520°C. These results are discussed in terms of the crystal‐structure model of Wang and others.

Variational principles in the linear theory of elasticity, involving the elastic polarization tensor, have been applied to the derivation of upper and lower bounds for the effective elastic moduli of quasi-isotropic and quasi-homogeneous multiphase materials of arbitrary phase geometry. When the ratios between the different phase moduli are not too large the bounds derived are close enough to provide a good estimate for the effective moduli. Comparison of theoretical and experimental results for a two-phase alloy showed good agreement.