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The development of different textile structures and their composites for automotive leaf spring applications were considered. Owing to the good mechanical performance of epoxy, it was used as the matrix material in advanced structural applications. Initially, the different textile reinforcement architectures considered were in the form of E-glass unidirectional (UD) tow, bidirectional (2D) plain weave, and 3D woven solid orthogonal and interlock structures. The effect of reinforcing structure on the damping and wear performance of the composites was analyzed for their utilization in automotive leaf springs. Later, four different 3D orthogonal structures were developed to investigate the influence of binder percentage on their damping and wear performance. The damping performance was analyzed in terms of free vibrations, hysteresis damping, and dynamic mechanical properties. A wear analysis was carried out to determine the effect of different reinforcing elements on the friction and specific wear. The 3D reinforced composites considered exhibited the optimum damping and wear behavior. [ABSTRACT FROM AUTHOR]

The NiTip/1060Al composites were prepared using a pre-aging and friction stir method (FSP) to enhance the low-temperature damping performance of the aluminum alloy and accommodate various service temperatures. The bonding between NiTi particles and the 1060Al matrix is well established after FSP, and no new phases are formed in the composites. The phase-transformation peak temperature of NiTip/1060Al composites gradually shifts to lower temperatures with increased aging temperature of NiTi particles. At room temperature, the 550°C-NiTip/1060Al composite exhibits superior damping performance, with an internal friction value 144% higher than that of the FSP-1060Al alloy. However, at −91°C, the 650°C-NiTip/1060Al composite demonstrates better damping performance, with an internal friction value 158% higher than that of the FSP-1060Al alloy. The NiTip/1060Al composites exhibit the internal friction peak of NiTi phase-transformation in the temperature range from −91°C to 60°C. This characteristic results in significantly better damping performance compared to the FSP-1060Al alloy and other high-damping aluminum matrix composites. [ABSTRACT FROM AUTHOR]

Fibers extracted from the fruits of plants are less investigated for engineering applications as composites along with the engineering polymers. This study holistically developed less explored palmyra fruit fiber/polyester composites with or without montmorillonite nanoclays inclusions. Fibers extracted from the Palmyra fruit through special process were either untreated or chemically surface treated to improve interfacial bonding via mechanical anchoring matrix into fiber surfaces for mechanical strength. Fiber composites were manufactured through compression molding route, and the nanoclays are dispersed into the matrix before being compressed. The effects of various surface treatments on the chemistry and morphology of fibers were studied using scanning electron microscopy and Fourier transform infrared spectroscopy. The effect of fiber surface treatment and nanoclay incorporation on free vibrational behavior concerning the natural frequency and damping factor was also examined. Free vibration tests reveal that fiber surface treatment substantially impacts the natural frequency and damping factor of palmyra fruit fiber-reinforced composites (PFFCs). Specifically, NaOH-treated PFFCs have the maximum flexural strength, corresponding to the highest natural frequency. In addition, introducing nanoclays increases the flexural modulus beyond that of original PFFCs. After fiber surface treatments and the addition of nanoclays, modal analysis revealed the increase in composite stiffness through the changes noted in the composite damping results. [ABSTRACT FROM AUTHOR]

In this study, the damping responses of uniform soil, equi-proportional fly ash, and local soil as a single unit were investigated. The large-strain cyclic triaxial tests were performed for the specimen compacted at the desired density (95%–99% of maximum dry density). The compacted specimens were tested under the loading frequency of 0.3–1 Hz with medium confinement of 70–100 kPa. Also, the unsymmetrical behavior of the hysteresis loop was analyzed using three different damping estimation approaches, i.e. symmetric hysteresis loop (SHL), asymmetric hysteresis loop (ASHL), and the modified American Society for Testing and Materials (ASTM) method. The outcome of the study shows for fly ash, local soil, and layered soil-ash, the ASHL technique has the highest damping value, followed by ASTM and then the SHL approach. The specimens prepared under high density and subjected to high confinement show low damping values. However, the specimens tested at high frequency exhibits high damping behavior. Similarly, the damping value of fly ash determined using the SHL and ASHL methods has a similar profile and reaches a maximum at 1% shear strain value before decreasing. The composite stratified deposit exhibits more dependency on relative compaction, confining pressure, and less on loading frequency. Based on the results, it is highly recommended to use the ASHL approach, especially under large strain conditions irrespective of soil type. The maximum damping ratio of stratified deposits is always in between the damping ratio of local soil and fly ash. The damping ratio of stratified soil and local soil is slightly larger than that of the other soils, although the damping ratio of fly ash is equivalent to that of the sand and clayey soil. These results may be helpful in the accurate determination of the damping properties of the layered soil-ash system that is required in the seismic response analysis.

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In this paper, a nonlinear reduced-order model based on neural networks is introduced in order to model vertical sloshing in presence of Rayleigh–Taylor instability of the free surface for use in fluid–structure interaction simulations. A box partially filled with water, representative of a wing tank, is first set on vertical harmonic motion via a controlled electrodynamic shaker. Accelerometers and load cells at the interface between the tank and an electrodynamic shaker are employed to train a neural network-based reduced-order model for vertical sloshing. The model is then investigated for its capacity to consistently simulate the amount of dissipation associated with vertical sloshing under different fluid dynamics regimes. The identified tank is then experimentally attached at the free end of a cantilever beam to test the effectiveness of the neural network in predicting the sloshing forces when coupled with the overall structure. The experimental free response and random seismic excitation responses are then compared with that obtained by simulating an equivalent virtual model in which the identified nonlinear reduced-order model is integrated to account for the effects of violent vertical sloshing. [ABSTRACT FROM AUTHOR]

This article performs an analytical study on the damping vibration behavior of metal foam nanocomposite plate reinforced with graphene oxide powders (GOPs) in thermal environment. The GOPs are dispersed through the thickness of the structure according to three functionally graded (FG) and one uniform distribution patterns. The Halpin–Tsai micromechanical model is chosen for estimating the effective material properties of the structure having GOPs as reinforcement phase. Also, different porosity types are taken into account for the metal foam matrix. The plate is resting on a three-parameter viscoelastic medium containing Winkler and Pasternak layers in combination with viscous dampers which can dissipate the oscillation of the structure in some special cases. The Governing differential equations are derived via Hamilton's principle on the basis of refined higher order shear deformation theory and then solved with employing Galerkin solution method to obtain the natural frequencies of the proposed structure. Moreover, various boundary conditions (B.Cs) including simply supported, fully clamped and different combinations of these B.Cs are considered in this study. The influences and confrontation of different significant parameters such as GOPs' weight fraction, foundation parameters, aspect and side-to-thickness ratios, porosity coefficients, thermal environment, and FG patterns are investigated through various graphical and numerical results. Our findings declare that the dynamic behavior of the graphene oxide powder reinforced metal foam (GOPRMF) plate remarkably depends on these parameters. [ABSTRACT FROM AUTHOR]

The damping behavior of continuous SiC fiber reinforced aluminum matrix (SiCf/Al) composite is still poorly understood. This paper examined the temperature dependence and strain amplitude dependence of damping capacities in 30 vol% SiCf/Al composites including SiCf/2024Al, SiCf/6061Al and SiCf/AlFe5Si2 composites, and the unreinforced aluminum alloys. Microstructure characterization was performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and X-ray diffraction (XRD) analysis to investigate the operative damping mechanisms in the SiCf/Al composites. The results show that uniform dispersion of SiCf and good interface bonding were achieved with these SiCf/Al composites. The damping capacity and dynamic modulus of these composites were greatly improved as compared with that of the unreinforced aluminum alloys. The dominant damping mechanisms for SiCf/Al composites were dislocation damping at low temperatures (< 150 ℃), and grain boundary damping and interface damping at high temperatures (> 150 ℃). This work indicated that the SiCf/AlFe5Si2 composite simultaneously exhibited good damping capacity and high dynamic modulus, having potential for aerospace applications. [ABSTRACT FROM AUTHOR]

An understanding of the fundamental correlation between grain size and material damping is crucial for the successful development of structural components offering high strength and good mechanical energy absorption. With this regard, we fabricated aluminum sheets with grain sizes ranging from tens of microns down to 60 nm and investigated their tensile properties and mechanical damping behavior. An obvious transition of the damping mechanism was observed at nanoscale grain sizes, and the underlying causes by grain boundaries were interpreted.

The aim of this investigation is to evaluate the size effects on the nonlinear free vibration of the sandwich composite microbeam with an extensible shape memory alloy layer in the midplane. A one-dimensional constitutive model is considered to simulate the pseudoelastic behavior of the shape memory alloy layer. The governing equation of motion is derived using the Euler–Bernoulli beam theory together with the modified couple stress theory through the Hamilton's principle. Midplane stretching and phase transformation of the shape memory alloy which are sources of nonlinearity were considered, and a numerical solution method is presented. A damped response of the sandwich composite microbeam is observed because of the hysteresis behavior of the extensible shape memory alloy layer in the midplane. Results are appraised by comparing with the available literature. The influence of material length scale, temperature, and initial velocity on the loss factor and other pivotal vibrational behavior is evaluated. Results show that increasing the material length scale to thickness ratio has a decreasing effect on damping capacity. [ABSTRACT FROM AUTHOR]

In the present study, Ni50Ti50 (NiTi) particle reinforced aluminum nanocomposites were fabricated using microwave sintering and subsequently hot extrusion. The effect of NiTi (0, 0.5, 1.0, and 1.5 vol %) content on the microstructural, mechanical, thermal, and damping properties of the extruded Al-NiTi nanocomposites was studied. Compared to the unreinforced aluminum, hardness, ultimate compression/tensile strength and yield strength increased by 105%, 46%, 45%, and 41% while elongation and coefficient of thermal expansion (CTE) decreased by 49% and 22%, respectively. The fabricated Al-1.5 NiTi nanocomposite exhibited significantly higher damping capacity (3.23 x 10-4) and elastic modulus (78.48 ± 0.008 GPa) when compared to pure Al. [ABSTRACT FROM AUTHOR]

Different thermal analysis techniques were used to study the effect of fillers and ionic liquids (ILs) on the vulcanization process, thermal and dynamic mechanical properties of acrylonitrile–butadiene elastomer (NBR). The products of the studies were composites of NBR filled with hydrotalcite, nanosized silica or carbon black. ILs such as 1-butyl-1-methylpyrrolidinium (BMpyrrolBF4), 1-butyl-4-methylpyridinium (BMpyrBF4) or 1-butyl-1-methylpiperidinium (BMpipBF4) tetrafluoroborates were applied to improve the dispersion degree of the curatives and filler particles in the elastomer and to increase the efficiency of vulcanization. The differential scanning calorimetry results indicated that ILs reduced the vulcanization temperature of NBR compounds and increased the homogeneity of cross-link distribution in the elastomer network. NBRs filled with carbon black or silica exhibited similar thermal stabilities, whereas hydrotalcite reduced the temperature of thermal decomposition. The lowest mechanical loss factors were determined for vulcanizates filled with nanosized silica. [ABSTRACT FROM AUTHOR]

The microstructure, phase composition, phase transition process, mechanical properties, and damping behavior of NiTip/6061Al laminar composites were investigated by introducing a NiTi particle layer with phase transition characteristics into the 6061 aluminum matrix using rolling composite technology. No defects, such as cracks or holes, were found in the NiTi particle layer, and no agglomeration of the NiTi particles was recorded. The interlayer interface between the alloy particle layer and the 6061Al matrix was clear and well-combined, and no new phase formation occurred in the composite. The composites exhibited phase transition characteristics similar to NiTi alloy particles, and the phase transformation temperature of the composites increased gradually with an extended aging time of the NiTi-reinforced particles. Following aging strengthening, the NiTip/6061Al laminar composites demonstrated higher yield strength than the 6061-T6 aluminum alloy, while their tensile strength remained similar. Pre-aging treatment of the NiTi particles had only a minor effect on the mechanical properties of the composites. The damping capacity of the laminar composites surpassed that of the 6061-T6 aluminum alloy due to the synergistic enhancement of phase transition damping from the NiTi particles and interparticle interface damping within the particle layer The internal friction values of the NiTip/6061Al laminar composites at 60 °C and 350 °C were up to 0.0134 and 0.1146, respectively, which were 211% and 313% higher than those of the 6061-T6 aluminum alloy at the corresponding temperature. The storage modulus and the comprehensive damping performance (E IF) of the NiTip/6061Al laminar composites were higher than those of the 6061-T6 aluminum alloy. • The phase-transition temperature of composites was changed by NiTi particles pre-aging. • NiTi particles pre-aging slightly affected the mechanical properties of the composites. • The composites exhibited excellent damping performance. • Synergistic effects reinforced the composites with phase transition and interface damping. [ABSTRACT FROM AUTHOR]

Dynamic mechanical analysis was used to investigate the damping behavior of a U–Nb shape memory alloy in various states, including water quenched (WQ), aging (AG), and cold rolling (CR). Internal friction peaks in the U–Nb alloy were identified, as well as their sensitivity to microstructure. The effects of amplitudes on internal friction and storage modulus were more pronounced in the WQ and AG samples than in the CR samples. A relaxation peak at 200 K was discovered in the U–Nb alloy, and its intensity decreased with aging, as did the activation energy for the relaxation event. It may be that the interaction between H and twin boundaries became more active as a result of the local concentration of Nb with aging. There are three transformation peaks in the current U–Nb alloy in the WQ and AG states, corresponding to phase transformations of α"→γ0 and γ0→γ, respectively. The damping behavior of the coarse-grained and fine-grained samples differs only slightly, and grain size (grain boundaries), is not believed to be directly responsible for the difference; instead, twin boundaries as damping sources may dominate the damping behavior of the U–Nb alloy. [ABSTRACT FROM AUTHOR]

In the present study, Ni50Ti50 (NiTi) particle reinforced aluminum nanocomposites were fabricated using microwave sintering and subsequently hot extrusion. The effect of NiTi (0, 0.5, 1.0, and 1.5 vol %) content on the microstructural, mechanical, thermal, and damping properties of the extruded Al-NiTi nanocomposites was studied. Compared to the unreinforced aluminum, hardness, ultimate compression/tensile strength and yield strength increased by 105%, 46%, 45%, and 41% while elongation and coefficient of thermal expansion (CTE) decreased by 49% and 22%, respectively. The fabricated Al-1.5 NiTi nanocomposite exhibited significantly higher damping capacity (3.23 × 10−4) and elastic modulus (78.48 ± 0.008 GPa) when compared to pure Al.

In the present study, aluminum based metal matrix composites containing various amounts of boron nitride (BN) nanoparticulates (0, 0.5, 1.0 and 1.5 vol.%) were fabricated by using the powder metallurgy (PM) technique involving microwave sintering and hot extrusion process. The microstructure, physical, thermal, mechanical and damping characteristics of the extruded nanocomposites were investigated. Field emission scanning electron microscopy (FE-SEM) study shows the evenly distributed BN particles in Al matrix. Mechanical analysis indicates that the compression, hardness and tensile strength of Al-BN nanocomposites increases with increasing amount of BN content. Particularly, a significant improvement in the tensile strength (∼36%) is achieved in Al-1.5 vol.% BN nanocomposite when compared to the pure aluminum (Al). This improvement strength can be attributed to the dispersion hardening of the Al matrix due to the presence of hard BN nanoparticles. Thermal analysis shows that the coefficient of thermal expansion (CTE) decreases with increasing amount of BN which may be ascribed to inherent low CTE of BN nanoparticles used as reinforcement. The addition of BN nanoparticulates enhanced the damping characteristics of pure Al with Al-1.5 vol.% BN nanocomposite exhibiting the maximum damping capacity and damping loss rate with a minimum change in elastic modulus. The improved combination of properties exhibited by Al-BN nanocomposites make them potential candidates for a wide spectrum of industries especially for weight critical applications. [ABSTRACT FROM AUTHOR]

Using recycled cathode ray tube (CRT) funnel glass as a substitute for sand contributes to both reducing natural aggregate consumption and the disposal of CRT funnel glass. Currently, most studies have focused on the mechanical and durability properties of mortar or concrete containing CRT glass as fine aggregate. However, the study of the dynamic loadings (e.g., earthquake load, wind load and impact load) of major concrete structures containing CRT glass is still limited. In this paper, a dynamic thermo-mechanical analysis test with various frequencies (0.1 Hz–2.0 Hz) and temperatures (−30 °C−30 °C) is undertaken on mortars with different CRT replacement ratios (0, 20%, 40%, 60%, 80%, and 100%). The test results show that the storage modulus (stiffness) of mortar with incorporated CRT glass is lower than that of control mortar in most cases, but the decreasing trend is not proportional to the CRT replacement ratio. However, the presence of CRT glass in the mix has a negligible impact on the frequency dependence of the storage modulus of mortar. The storage modulus of each replacement ratio is nearly constant for all excitation frequencies. The frequency dependence of loss tangent (damping behavior) is significantly improved with CRT glass under 0 °C. This indicates that a frequency dependent damping model is needed when dynamic analysis is conducted on concrete structures with incorporated CRT glass in cold weather. [ABSTRACT FROM AUTHOR]

This paper presents 2 models to simulate the damping behavior of a 12-story vertically mixed structure with upper steel and lower concrete substructures (S/RC structure). One is the modal strain energy damping model based on modal damping ratio. The other is the assembled Rayleigh damping model based on damping matrix that is obtained by combining Rayleigh damping matrix of steel components with that of concrete ones. Then a 12-story S/RC frame and a 12-story RC frame are designed and used for shaking table test. Based on the test, the expressions for the damping behavior of steel and concrete substructures of the S/RC frame are derived, and these expressions are utilized to form 2 different damping models of the S/RC structure separately. By comparing the damping behavior of the 2 models in analysis with what has been identified in the tests, the feasibility of the 2 models are assessed in both frequency domain and time domain. Theoretical analysis and experimental results show that the assembled Rayleigh damping model is not applicable to conventional modal analysis because of its nonproportional characteristics. However, the modal strain energy damping model based on equivalence of the dissipated modal strain energy of structure, which embodies the essence of damping, can give better predictions on damping behavior of the S/RC frame in both time and frequency domains. Finally, some suggestions are put forward on the selection of damping parameters in practical seismic design for vertically mixed structures. [ABSTRACT FROM AUTHOR]

Recycled WPC product using in construction industry occasionally falls short of expectation owing to lack of sufficient ductility and damping capacity, ground waste rubber tire (WTR) with substantial elasticity can be a proper candidate to meet the gap when adding appropriately. Here, WTR after alkali activation was blended in waste wood flour (WWF) treated with compatibilizer, the mixture after oven-dried was subsequently filled into thermoplastic recycled polyethylene (RPE) or polypropylene (RPP) base (WTR/WPC) through hot-press molding process. Mechanical properties (tensile strength ft, flexural strength fb, impact strength fa) of RPE-based and RPP-based WTR/WPC strips with 4 different WTR fractions were characterized. Its damping properties (loss factor η) were measured and identified by ultrasonic agitation and half-power bandwidth identification method, respectively. The coarse WTR has balanced but stable effect on the improvement of ft, fb, fa, and η of WTR/WPC with rigid RPP base than that with flexible RPE, which attributes to the synthetic effects of good deformation capacity of coarse WTR themselves, strong bridging capacity of WWF, and sufficient stick-slip intercalation between WWF or WTR and rigid RPP. The ft, fb and fa, η with 5% coarse WTR of RPP-based WTR/WPC reaches 12.32 MPa, 15.74 MPa; 2.58 MPa and 0.0853, respectively. [ABSTRACT FROM AUTHOR]

• The microstructural features of Ti-Nb alloys were tailoring by changing Hf contents. • The damping behavior and functional performances of Ti-Nb alloys were dependent on Hf contents. • The mechanisms for the evolution of damping behavior and functional properties in Ti-Nb-Hf alloys were clarified. In the present study, the electron concentration, bond order and metallic average d-electron orbital energy level of Ti-Nb-Hf shape memory alloys were controlled by adjusting the Hf content, which further determined the phase constituents and phase stability. The Ti-Nb-Hf shape memory alloys with various Hf contents were composed of the α´´ martensite phase and β phase, regardless of Hf contents. With increasing Hf content, the martensitic transformation temperature (Ap) slightly increased. Hf addition could enhance the strength and optimize the strain recovery characteristics. A higher strength and larger recoverable strain can be obtained in Ti-Nb shape memory alloy modified by 2 at.% Hf due to grain refinement, precipitation strengthening and solution strengthening. Training can achieve perfect superelasticity with a completely recoverable strain of approximately 2%. In conclusion, the perfect combination of damping capacity and strain recovery characteristics can be attained by tailoring the Hf content in Ti-Nb-Hf shape memory alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

A brief outline was prepared to study the effect of nano-SiC p reinforcement on the structural features, mechanical and physical properties of the continual annealing and roll-bonding (CAR) processed aluminum foam. Nanoindentation, drop weight impact and operational modal tests were applied to evaluate mechanical and physical properties of the nanocomposite foam. Scanning electron microscopy and elemental distribution images were utilized to analyze the results. Findings showed that the application of nano-SiC p results in matrix strengthening and remarkable improvements in dynamic compressive properties (strength increase of 48%), energy absorption (35% increase) and damping behavior (77% increase in damping ratio) of the nanocomposite foam. [ABSTRACT FROM AUTHOR]

A micromechanical stick-slip model was developed to characterize the damping response of single-walled carbon nanotube nanocomposites. Depending on the strength of the interfacial bonding and the extent of applied loading, the single-walled carbon nanotube embedded in the matrix may either completely stick to the matrix or partially slide relative to the matrix. The slippage in the interface, together with the contact friction, may lead to the energy dissipation of single-walled carbon nanotube nanocomposites. The effects of the aspect ratio of single-walled carbon nanotube, interfacial bonding strength, volume fraction of single-walled carbon nanotube, and interfacial friction on the damping behavior of single-walled carbon nanotube nanocomposites were accounted for in the micromechanical stick-slip model. In order to validate the analytical model, the energy dissipation was also evaluated using the finite element method. A cylindrical finite element method, with an embedded single-walled carbon nanotube, was developed where the stick-slip behavior of the interface between the single-walled carbon nanotube and surrounding matrix was characterized using a contact element. It was found that the energy dissipation obtained from the finite element analysis agrees with that derived from the micromechanical stick-slip model. Moreover, the energy dissipation may significantly increase, when the single-walled carbon nanotube slippage takes place. The increment of the energy dissipation could be attributed to the interfacial contact friction between the single-walled carbon nanotube and the surround matrix as well as the viscoelastic properties of the matrix materials. [ABSTRACT FROM AUTHOR]

In present work, effect of Nb content on martensitic transformation and damping behavior of (Ti 50 Ni 38 Cu 12 ) 100-x Nb x (x = 0, 5, 10, 15at.%) shape memory alloys was investigated by means of X-ray diffraction, differential scanning calorimetry and dynamic mechanical analysis. As a result, the transformation sequence of TiNiCuNb alloys is found to be B2→B19→B19′ upon cooling. Two different damping peaks are observed, one is related to B2→B19 transformation and the other one is related to the overlapping of twin relaxation-type and B19→B19′ transformation. With increasing Nb content to 15 at.%, the peak value of damping capacity of B2→B19 transformation slightly decreases. [ABSTRACT FROM AUTHOR]

• An innovative graphene oxide/TiNi laminate composite sheet was designed and prepared. • The continuous Ti 2 Ni and TiC reaction layers were generated along the GO/TiNi interface without obvious disjunct. • The composite sheet showed superior damping properties than TiNi alloy and TiNi laminate sheet without GO. In this paper, the interfacial microstructure and damping behavior of the novel graphene oxide/TiNi laminate composite sheet (GO/TiNi) were characterized. Results showed that the well-bonded GO/TiNi interface and alternating laminate structure were obtained in the composite sheet. The continuous reaction layer adjacent to the TiNi matrix was detected as the Ti 2 Ni phase with cubic structure, and the reaction layer near the GO was confirmed as the TiC nanocrystalline. The rhombohedral Ni 4 Ti 3 phase could be tracked to precipitate within the TiNi matrix. Compared with the TiNi alloy and TiNi laminate sheet without GO, the GO/TiNi laminate composite sheet has the optimal intrinsic damping capacities with the tanδ (martensite) of 0.089 and tanδ (austenite) of 0.034, which are attribute to the effective introduction of the high damping GO reinforcement. [ABSTRACT FROM AUTHOR]

Acoustically transparent elastomers are the windows through which the US Navy views the ocean. For acoustic clarity and sensitivity, it is important that these elastomers operate well outside damping conditions as dictated by the temperatures and frequencies of interest. Damping behavior is characterized by a peak in the loss tangent and is associated with transitions in molecular mobility, such as the primary glass-rubber or alpha transition. However, the temperature and frequency location of this peak can shift in response to absorbed plasticizing fluids. This material characteristic is under investigation using dynamic mechanical analysis to assess its dependence on the plasticizer and polyurethane component chemistry. In this second stage of the research, the time-temperature superposition technique was employed to extrapolate storage modulus and loss factor to frequencies beyond the limits of the equipment. The technique appears to be valid for plasticized primary transition behavior but becomes circumspect when applied to secondary transition behavior. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Al content is related with structural relaxation and damping capability. [•] Dynamic modulus is insensitive to the frequency especially for storage modulus. [•] Several internal-friction peaks are observed in the Al-free or Al-lean alloys. [•] The damping behavior is proposed to be strongly relied on the level of ordering. [Copyright &y& Elsevier]

The aim of the present investigation is to probe the influence of organically modified layered silicates (o-montmorilonite, o-MMT) content on mechanical and thermal behaviors of vinyl ester/o-MMT (organoclays) nanocomposites. Polyvinyl ester nanocomposites were synthesized with o-MMT by in-situ polymerization technique. The prepared vinyl ester/o-MMT composites have been characterized for mechanical properties such as tensile properties and impact strength. Thermal characteristics of the vinyl ester/o-MMT nanocomposites were evaluated by using differential scanning calorimeter (DSC), thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMA). The thermal degradation kinetic parameters such as activation energy (Ea) of nanocomposites were evaluated by using three mathematical models, namely Horowitz-Metzger, Coats-Redfern and Broido's methods. [ABSTRACT FROM AUTHOR]

The present work aims to investigate the internal friction and effect of pre-deformation on damping capacity of Nb60Ti25Ni15 alloy, which could be considered as TiNi/NbTi metal matrix composite. The internal friction results showed that this composite possesses excellent damping behavior, which is associated with the movement of a set of abundant interfaces, such as those between the TiNi and NbTi phases, those between martensitic variants and those between martensite and parent phase. Meanwhile, the peak temperature and the width of the internal peak increased with increasing of prestrain level. It appears to be due to the release of the stored elastic strain energy, or the pinning effect by the deformed structures. Furthermore, the height of internal friction peak decreased as the prestrain level increased. [ABSTRACT FROM AUTHOR]

The use of thermoplastic composite materials in aerospace and naval fields has increased due principally to their high performance associated with low specific weight. In order to screen material behavior, the effects of external environments on the mechanical properties during usage must be clearly understood. Environmental factors such as ultraviolet radiation (UV), corrosive fluids, moisture and temperature can limit the applications of composites by deteriorating the mechanical properties over a period of time. In order to characterize composite materials, are commonly used tensile tests. Another test that can be used in order to evaluate the viscoelastic properties of thermoplastic composite materials is free vibration damping. In this work, the viscoelastic properties of polyamide 6.6/carbon fiber laminates were obtained by two types of tests: tensile and free vibration damping tests. Two families of textile polyamide/carbon fiber composites ([±45] and [0/90]) were obtained by hot compression molding. The present studies have been performed to explore relations between the dynamic mechanical properties and the influence of high moisture concentration of this thermoplastic laminate. The results show that the E' decrease with the increase in the exposed time for polyamide/carbon fiber composite specimens and that free vibration damping technique can be used instead of tensile test in order to know the elastic modulus. [ABSTRACT FROM AUTHOR]

ABSTRACT: An attempt has been made to develop fly ash filled polymer matrix composites with high damping behavior. Fly ash filled polymer matrix composites do not show very high damping property and this limits their application in many fields. Hence, unsaturated polyester resin (UPE) was blended with SBR latex in three proportions and this blend was used as the matrix for making the composites. Both 40 and 50wt% fly ash loaded blend matrix composites were prepared by the room temperature casting method. Flexural properties were investigated. The damping behaviors of the composites were determined by dynamic mechanical analysis (DMA). The presence of latex particles significantly enhanced the damping property. The combination of damping behavior with good mechanical property was optimized. UPE resin blended with 5wt% SBR latex was found to have good strength with enhanced damping property. Very high damping can be achieved with the UPE/10wt% SBR latex blend matrix having 50wt% fly ash loading. The fracture surfaces examined under SEM revealed good compatibility between the various components of the systems. [ABSTRACT FROM AUTHOR]

Unsaturated polyester resin is extensively used in the fiber reinforced composite industry and very often, their failure starts from the microcracking of the matrix resin. UPE resin, being a thermoset material, becomes very rigid after crosslinking and has poor energy absorption characteristics. To enhance its stress absorbing behavior in dynamic conditions, an attempt was made by blending it with SBR latex in three proportions (1, 5, and 10%). The three sets of samples were subjected to flexural testing and dynamic mechanical analysis. A 50% and 22% increase in modulus were observed in case of 1% and 5% latex added samples respectively. This indicates a strong intercomponent bonding in these samples. In the 10% latex added blend, the latex particles were evident as discrete phases in the continuous resin matrix. The flexurally fractured surfaces were examined under a scanning electron microscope. Their static and dynamic mechanical properties were correlated with their microstructure. [ABSTRACT FROM PUBLISHER]

• Pure Al particle layer reinforced 7075 Al composite fabricated by hot rolling. • Al p /7075Al lamellar composite shows well mechanical and damping properties. • Comprehensive damping index of the composite is 2.9-fold of that of the 7075 Al matrix. • Effect of Al particle layer on damping mechanism of the composite was analyzed. The Al particle reinforced 7075 Al matrix composites with the layered structure are prepared by hot rolling to improve the damping property of the alloy. Numerous interparticle interfaces are observed in the Al particle layer (reinforcement), and the traces of no interfacial reaction or elemental diffusion are found between the matrix and reinforcement layer. The tensile strength of the composite is 29% higher than that of the matrix. The internal friction values of the Alp/7075Al lamellar composite and the 7075 Al matrix are found to increase with the increase in temperature and strain, respectively. At 570 K, the internal friction values of the composites are found to be as high as 0.105, which is 337% higher than that of the matrix, and an internal friction peak (P 2) appears in the composites due to the recrystallization of Al particles at high temperature. The comprehensive damping index of the composite is found to be about 2.9-fold of the 7075 Al matrix. The damping mechanism of the composite is mainly attributed to dislocation damping, grain boundary damping, and interface damping. [ABSTRACT FROM AUTHOR]

Ecoceramics is a porous carbon material which is proved to have some favorable characteristics. With the purpose of enlarging the application fields of ecoceramics, an ecoceramics/ZK60A (ECMs/ZK60A hereafter) composite was fabricated using high-pressure vacuum infiltration technique. Microstructural analysis and measurements of mechanical properties as well as damping behavior of ECMs/ZK60A composite were made. Experimental results show that ZK60A filled most of the pores and ECMs/AlSi composites have a topologically uniform interconnected network microstructure. ECMs/ZK60A composite exhibited superior mechanical properties as compared with uninfiltrated ecoceramics. It is believed that strengthening effect was caused by strengthening of ZK60A, crack bridging by the ductile phase and interlocking structure between components in ECMs/ZK60A composite. Damping values of ECMs/ZK60A composite improve based on those of ecoceramics. They increase with testing temperature but decrease with increasing vibration frequency. [Copyright &y& Elsevier]

There is a trend to design the turbine coating and the substrate as in integral, layered, engineering assembly. Under the harsh environment of the turbine engine, a failure in one component can quickly lead to failure in other components. Materials that are used in structural applications are prone to mechanical vibration, which, when not attenuated, will lead to fatigue of components and shortening of life cycle. Therefore, it is necessary to examine the thermal stability and dynamic mechanical properties of coatings under dynamic conditions. In addition to these noise reduction and vibration amplitude control motivated objectives, however, mechanical energy dissipation processes also find intrinsic applications in cases for which a thorough understanding of the mechanisms responsible for the damping response of the material is required. This article describes the damping behavior and mechanisms that exist in plasma sprayed NiCoCrAlY coatings. [ABSTRACT FROM AUTHOR]

Experiments have been carried out to investigate the damping behavior of foamed commercially pure aluminum (FA). The FA specimens were prepared using pressure infiltration process. The damping characterization was conducted on a multifunction internal friction apparatus (MFIFA). The internal friction (IF), as well as the relative dynamic modulus, was measured at frequencies of 0.5, 1.0 and 3.0 Hz over the temperature range of 20–400 °C. The size of macroscopic pore is on the order of a millimeter (1.0 mm) and in large proportions, typically up to 69 vol.%. The measured IF shows that FA has a damping capacity that is enhanced in comparison with bulk commercially pure aluminum. Especially, an IF peak was found and corresponding to a rapid drop of relative dynamic modulus (vs. temperature) in the FA specimen. The average values for the activation energy of the IF peak is approximately 1.39±0.03 eV. The microstructural analysis was performed using transmission electron microscopy (TEM). TEM observations showed that dislocation substructures exist near the grain boundaries. Accordingly, one can propose that such substructures intersecting and interacting with the grain boundaries are dragged along with the grain boundary during the viscous sliding of the boundary, so that the sliding process is limited with the appearance of this IF peak. Finally, a four-parameter mechanical model used for describing the operative damping mechanism of the IF peak in the FA were discussed in light of IF measurements and microstructural studies. An approximate expression for IF is derived, which is based on the four-parameter mechanical model in FA specimen and the experimental results have been better explained. [Copyright &y& Elsevier]

• Porous structure and large numbers of interparticle interfaces are formed in the particle layer. • Damping capacity and storage modulus are simultaneously improved by the particle layer. • The comprehensive damping index of the composites is superior to the 5052 Al alloy. • The damping mechanism of AlSi30 p /5052Al composites was analysed. The AlSi30 p /5052Al composite with porous particle layer was successfully produced by hot rolling. Numerous interparticle interfaces and pores were seen in the particle layer. The dynamic mechanical analysis shows that the internal friction and the storage modulus of the composites are higher than that of the matrix. Due to the presence of an intermediate particle layer, dislocation and residual internal stress increase in the composites, and thereby improve the storage modulus of the composites. The comprehensive damping index of the composites is better than that of the matrix. The synergistic damping effect caused by the porous structure and a large number of interfaces between particles in the particle layer improve the damping capacity of the composites. [ABSTRACT FROM AUTHOR]

• The peak value of relaxation damping peak increases and then decreases with the increase of irradiation dose. • The relaxation IF increases from 0.04 to 0.055 with a wide span of temperature range after electron irradiation at 2 × 1017 e/cm2. • The isothermal IF of twin boundary relaxation damping remains stable with a span of 160 ℃ (IF>0.03) from 50 ℃ to 210 ℃. Damping devices need to maintain a high internal friction value in a wide high-temperature range in an aviation environment. Damping behavior is sensitive to defects including vacancies, interstitials, and dislocations. Electron irradiation is an effective method to introduce defects into materials to tailor the damping properties. The relaxation internal friction peak value increases first and then decreases with the increase of irradiation dose in Ni 54 Mn 25 Ga 21 alloy. The peak value increases from 0.04 to 0.055 by 37.5% after irradiated by 1.2 MeV electrons at 2 × 1017 e/cm2. It derives from the effect of dislocations on the interaction between interstitials and twin boundaries. The high isothermal internal friction remains stable with a large working temperature range of 160 ℃ from 50 ℃ to 210 ℃. This research provides a new method to obtain high damping Ni 54 Mn 25 Ga 21 alloy with a wide high-temperature range. [ABSTRACT FROM AUTHOR]

• SLMed specimens are studied in as-built configuration and after thermal treatments. • Variations of tensile properties, residual stresses, damping capacity are evaluated. • Experimental results show that damping response is related to residual stresses. • Thermal treatments can modulate residual stresses and damping capacity. In the Additive Manufacturing (AM) field, Selective Laser Melting (SLM) process is one of the most promising manufacturing technologies for the production of 3D complex parts. High-tech sectors, like aerospace, show growing interest for the use of AM, because it can offer unique opportunities in terms of freedom in the design and integration of some specific functionalities in lightweight structures. Together with lightness of materials, another important requirement is the capacity of vibrations damping, relevant e.g. for the vibro-acoustic environment during launch in the aerospace field. This work focuses on the correlation between the damping behavior of AlSi10Mg specimens and residual stresses induced during SLM, i.e. in as-built condition, or after different post-additive heat treatments, specifically studied for this Al alloy. Indeed, residual stresses have a well-known influence on the static and fatigue mechanical behavior, but a few literature works are present relating residual stresses with damping capacity. Results of the performed experimental tests showed that the damping capacity decreases with the increase of the heat treatment temperatures, i.e. damping can be modulated by customized thermal treatments. [ABSTRACT FROM AUTHOR]