Mechanical Damping Properties Research Articles

Experimental characterization of acoustic damping materials

AbstractDue to their ease of use and low cost, passive damping methods are a preferred mean for the reduction of noise in many engineering applications. This applies in particular to foam materials, which exhibit good acoustic and mechanical damping properties. The selection of suitable materials is usually carried out experimentally and can be very labor‐intensive and time‐consuming. For this reason, it is helpful to develop qualified numerical methodsthat can be used for material design and selection. Hence, foam materials must be characterized experimentally in order to enable a later comparison with vibroacoustic simulations. This contribution, therefore, aims at providing suitable parameters for the use in numerical analyses and their validation. Firstly, the microstructure of a foam specimen is captured by means of a CT scan. In addition to providing the geometry for the multi‐physics simulations, this measurement is also used to determine characteristic foam features, for example, strut thickness and pore size distribution. In the second step, the frequency‐dependent stiffness and damping properties of the material are determined by a special experimental setup utilizing an electrodynamic shaker. Here, the dynamic system is approximated as a single‐mass oscillator, which is sufficiently accurate for low frequencies. These properties will later be used in the numerical model to evaluate different parameter identification approaches. In the third and last step of the experimental campaign, measurements with an impedance tube are conducted to obtain the coefficient of absorption. This material parameter is particularly suitable for comparing experiments and simulations. Finally, the correlation between the experimental results is examined to provide a deeper understanding of the foam materials.

Multifunctional architected MWCNTs/PDMS composites with high sensing and energy absorption capability inspired by ant tentacle and pomelo peel

The multifunctional features of pressure sensitivity and energy-absorption capability of flexible electromechanical sensors are desirable for practical applications, such as personal protection, crash mitigation, and protective packaging of sensitive elements. However, there are still challenges in developing ultrasensitive pressure sensors with high energy absorption capability. Herein, a bio-inspired flexible piezoresistive MWCNTs/PDMS composite with a multilayered architecture mimicking the ant tentacle and the pomelo peel is innovatively constructed, which can simultaneously detect physical stimuli in an extensive pressure range and absorb impact energy. The composite architecture is composed of the bottom-layer interlocked tentacle-like conical micropillars and the top-layer pomelo peel-inspired hierarchically enclosed-porous microstructure, which has successfully wrapped air inside to form a solid-gas dual phase structure with enhanced energy absorbing capability and piezoresistivity. The composite architecture was manufactured by a laser-engraving method associated with the controlled solidification process of the composite by regulating the vacuum pumping rate in the pre-curing condition. Owing to the hollow-shaped tentacle-like conical micropillars, the contact area can be dramatically increased within a subtle pressure loading, leading to superb pressure sensitivity of ∼26.1 kPa−1. Simultaneously, the hierarchically enclosed-porous structure with trapped air (gas-phase), acting as an air cushion packaging, imitating the pomelo peel provides the composite architecture with exceptional mechanical energy absorption of ∼2.74 MJ/m3 and an extensive pressure sensing range from 0.1 Pa to 60 kPa. As a result, the as-proposed composite sensor was able to detect mechanical signals such human finger tapping, wrist flexion, and pendulum hammer impact. Numerical simulations also showed that the wrapped air inside the hierarchical enclosed-porous structure improved the mechanical damping properties of the composite architecture. It is envisioned that our finding could contribute to the development of multifunctional materials to meet the growing demands for next-generation electronic systems, inspired by sophisticated architectures from nature.

Foam/Film Alternating Multilayer Structure with High Toughness and Low Thermal Conductivity Prepared via Microlayer Coextrusion

Multilayer membranes prepared via microlayer coextrusion have attracted wide attention due to their unique properties and broad applications. In present study, the foam/film alternating multilayer sheets based on ethylene-vinyl acetate copolymer (EVA) and high-density polyethylene are successfully prepared via microlayer coextrusion. The cells in the sheets are single-cell-array along the foamed EVA layers with uniform cell size. In addition, the effects of layer number and foam relative thickness on morphology, mechanical properties, damping and heat insulation properties are investigated. The cell size decreases significantly with increasing layer number due to the enhanced confine effects. The tensile strength, elongation at break, and heat insulation also increase significantly. However, the mechanical damping properties change little in the observed frequency. Meanwhile, with higher relative thickness of EVA foam, the sheets have lower tensile strength and lower thermal conductivity, while the damping properties are enhanced in a specific frequency scope. The elongation at break of the optimized sample comes to 800% and the thermal conductivity decreases to 61 mW·m−1·K−1, which shows high toughness and low thermal conductivity, indicating a possible method for preparing materials with high toughness and heat-insulating properties.

Heat dissipative mechanical damping properties of EPDM rubber composites including hybrid fillers of aluminium nitride and boron nitride.

As highly integrated electronic devices and automotive parts are becoming used in high-power and load-bearing systems, thermal conductivity and mechanical damping properties have become critical factors. In this study, we applied two different fillers of aluminium nitride (AlN) and boron nitride (BN), having polygonal and platelet shapes, respectively, into ethylene-propylene-diene monomer (EPDM) rubber to ensure improved thermo-mechanical properties of EPDM composites. These two different shapes are considered advantageous in providing effective pathways of phonon transfer as well as facilitating sliding movement of packed particles. When the volume ratio of AlN : BN was 1 : 1, the thermal conductivity of the hybrid-filler system (EPDM/AlN/BN) increased in comparison to that of the single-filler system (EPDM/AlN) of 3.03 to 4.76 W m-1 K-1. The coefficient of thermal expansion (CTE) and thermal distortion parameter (TDP) substantially decreased from 59.3 ppm °C-1 and 17.5 m K-1 of EPDM/AlN, to 39.7 ppm °C-1 and 8.4 m K-1 of EPDM/AlN/BN, representing reductions of 33 and 52%, respectively. Moreover, the damping coefficient of EPDM/AlN/BN was greatly increased to 0.5 of at 50 °C, compared to 0.03 of neat EPDM. These excellent performances likely stem from the effective packing of AlN/BN hybrid fillers, which could induce facile energy transfer and effective energy dissipation by the sliding movement of the adjacent hybrid fillers in the EPDM matrix.

Enhanced viscoelastic properties of nickel–aluminum–bronze alloyed with indium or its alloys

Engineering structures may be sensitive to vibrations such that their normal functioning is impaired due to the presence of vibrations. A material capable of dissipating energy of vibration by means of heat tends to have better mechanical damping properties. However, due to the demands on structural stability, the material needs to have sufficient stiffness to be useful structurally. Thus, the material must have both high stiffness and high mechanical damping. This paper discusses a variety of materials that were uniquely developed to achieve the aforementioned objectives. The new nickel–aluminum–bronze (UNS C95800)-based samples were classified according to alloying composition by weight percentage with different indium alloys. A dynamic mechanical analyzer was used to find the complex modulus (|E*|) and loss tangent (tan δ) values of the samples. These values were used to evaluate and compare the figure-of-merit (FOM) across different frequencies at a particular temperature and strain. The samples which have FOM equal to or greater than 0.6 GPA include the ones alloyed with pure indium (5 wt%), eutectic solder (5 wt%), indium–bismuth eutectic (10 wt%), bismuth–tin eutectic (5 and 10 wt%), and indium–tin eutectic (5 wt%). The newly alloyed high-damping metals can be used to reduce vibration while maintaining their stiffness.

Mechanical damping behavior of Al/C60-fullerene composites with supersaturated Al–C phases

Al-based materials with enhanced mechanical damping properties are of great interest in aerospace and automotive industries as engineering materials for critical components that suffer from severe dynamic environment. In this report, we developed Al/C60-fullerene composites to increase damping capacity by the supersaturated Al–C phases. Carbon atoms, dissolved from individually dispersed C60-fullerenes, are intercalated into the Al interstitial sites, producing Al–C phases with expanded lattice structures. These novel nanostructures exhibit a superior mechanical damping behavior compared to monolithic Al, throughout the temperature range of room temperature to 350 °C. The present approach to control the lattice structure thus represents a new engineering paradigm for atomic-level design of lightweight structural components.

Effect of Layering Pattern on the Mechanical Properties of Bark Cloth (Ficus natalensis) Epoxy Composites

The quest for sustainable materials as a consequence of a global drive to mitigate climate change has led to a focus on natural fiber–reinforced composite materials. In this study, skillful ply angle arrangement of bark cloth–reinforced laminar epoxy composites was carried out for the first time using vacuum-assisted resin transfer molding, and the composites fabricated were characterized for the effect of the layering pattern on their static and dynamic mechanical properties. Tensile strength and flexural strength were shown to be dependent on the ply angle arrangement. Dynamic mechanical analysis of the composites showed a glass transition temperature of 70°C, and the storage modulus and mechanical damping properties showed that the developed composites can withstand considerable loads and have excellent fiber-to-matrix adhesion.

Investigation of the Damping Properties and the Sound Insulation Performances of Fiber-reinforced Composites

Filling organic or inorganic fibers into the viscoelastic materials is a usual approach to modify their mechanical damping behaviors. The objective of this work is to study the mechanical vibration damping behavior and the sound noise reduction capability of the fiber-reinforced composite materials as well as to explore the correlation between the damping behaviors and the sound insulation performances. The samples were prepared by blending and solidification processes from ordinary commercial available damping slurries and various kinds of fiber fillers. The mechanical damping properties (including elastic modulus and loss factor) were measured by the dynamic mechanical analyzer (DMA). The sound insulation performances (indicated as acoustic transmission loss) were characterized by a sound impedance tube. The experimental results reveal that fiber fillers strongly affect the damping properties of the viscoelastic damping composites. The acoustic transmission loss curves are also affected.

Functionalized Metallic Hollow Sphere Structures

Metal hollow spheres (MHS) and metal hollow sphere structures are special types of cellular metals with an enormous application potential in structural and functional applications. A lot of effort has been made during the last two decades in order to develop the manufacturing process and to investigate the properties of this type of structure. Additional functionalizing of MHS is possible by filling the spheres with ceramic powders or phase change materials. Furthermore, by coating the spheres with different ceramic layers new properties and functions are added. Thus, the structures show excellent mechanical damping properties as well as high heat capacity for thermal storage and fast heat loading and unloading. Grinding or ceramic coating bring more functions to the surface of the spheres. The manufacture and properties of different types of functionalized MHS and their possible applications are highlighted here.

Phase transition and mechanical damping properties: A DMTA study of NiTiCu shape memory alloys

Internal friction measurement is a well-known investigation technique of the damping property of shape memory alloys (SMAs). It has already been demonstrated that this practice conducted in temperature scanning at a constant solicitation frequency is also useful in determining the path of the martensitic transformation and also the influence of hydrogen content on the martensitic properties. There is indeed a lack of studies about SMA internal friction as a function of solicitation frequency; systematic and rigorous analysis has not been reported yet. In this work the path of the martensitic transformation of Ni50−xTiCux alloys (x = 3–10at%) is investigated through Dynamic Mechanical Thermal Analysis (DMTA): internal friction as a function of temperature at a constant flexural frequency and internal friction as a function of flexural frequency at a constant temperature were evaluated. Results show that the two scans are both sensitive to phase transitions and microstructural changes.

Mechanical Damping Properties of Silicone Rubber Prepared by Nano-SiO<sub>2</sub> and AGE-Modified Polysiloxane Blends

The synthesis of AGE modified polysiloxane was realized by block copolymerization. Using degradation method and different ratio of raw materials, different content of AGE side chains and molecular weight of AGE modified polysiloxanes had been obtained. AGE modified silicone rubber was prepared by Nano-SiO2and AGE-Modified Polysiloxane Blends. The relationship between the molecular weight of AGE modified polysiloxane, the content of AGE modified side chains and the mechanical properties of AGE modified silicone rubber had been studied. The results showed that AGE modified silicone rubber had better mechanical damping properties than silicone rubber without modification of AGE: lower Tg (-56°C), higher tanδ (0.26), the maximum tensile/rear strengths with appropriate dynamic viscosity (17500mP•s) and the characterization of decreasing tensile/tear strengths with the increasing content of the AGE modified side chains.

Correlation between mechanical damping and interphase content in interpenetrating polymer networks

AbstractRecently, some interpenetrating polymer networks with good mechanical damping properties have been synthesized. However, the effect of morphology on this property has not yet been clearly elucidated. Herein, two polystyrene–polyurethane interpenetrating polymer networks, which were grafted using TMI [benzene‐1‐(1‐isocyanato‐1‐methyl ethyl)‐3‐(1‐methylenyl)] and HEMA (2‐hydroxyethyl methacrylate), respectively, have been investigated, as model samples, by modulated‐temperature differential scanning calorimetry and by dynamical mechanical thermal analysis. The results indicate that there is a correlation between mechanical damping and both interphase content and the distribution of composition in the interphase region. The findings should provide valuable information for the design of future damping materials. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2439–2442, 2001

Mechanical and mechanical damping properties of binary blends of chlorinated polymer with a special organic compound (DCHBSA)

Mechanical and mechanical damping properties of binary blends of chlorinated polymer with a special organic compound (DCHBSA)

Damping properties of aluminium foams

The mechanical damping properties of aluminium foams were measured. An experimental apparatus for measuring the loss factor avoiding parasitic damping is described. The difficulties, originating from random spatial density variations, are discussed. A procedure to overcome the problems is proposed and tested. The measured loss factors show that aluminium foams have a damping capacity which is enhanced in comparison with most massive cast aluminium alloys and increases with increasing porosity level.

Characterization of the damping properties of die-cast zinc-aluminum alloys

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.