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Micro structures of viscoelastic materials (VEM) play an important role in their mechanical properties and energy dissipation capacities. This work shows a mathematical modeling of VEMs considering...

This paper aims to develop viscoelastic dampers, which can effectively suppress vibration in a wide frequency range. First, several viscoelastic materials for damping performance were selected, and different batches of cylindrical viscoelastic dampers were fabricated by overall vulcanization. Second, the dynamic mechanical properties of the cylindrical viscoelastic dampers under different amplitudes and frequencies are tested, and the hysteretic curves under different loading conditions are obtained. Finally, by calculating the dynamic mechanical properties of the cylindrical viscoelastic dampers, the energy dissipation performance of these different batches of viscoelastic dampers is compared and analyzed. The experimental results show that the cylindrical viscoelastic damper presents a full hysteretic curve in a wide frequency range, in which the maximum loss factor can reach 0.57. Besides, the equivalent stiffness, storage modulus, loss factor, and energy consumption per cycle of the viscoelastic damper raise with the frequency increasing, while the equivalent damping decreases with the increase of frequency. When the displacement increases, the energy consumption per cycle of the viscoelastic damper rises rapidly, and the equivalent stiffness, equivalent damping, storage modulus, and loss factor change slightly.

The frequency dependence modeling of viscoelastic (VE) materials faces the challenge of high modeling accuracy over a wide frequency range and double-objective optimization in model paramet...

The magnetorheological elastomer (MRE) is a kind of smart material, which is often processed as vibration isolation and mitigation devices to realize the vibration control of the controlled system. The key to the effective isolation of vibration and shock absorption is how to accurately and in real time determine the magnitude of the applied magnetic field according to the motion state of the controlled system. In this paper, an optimal fuzzy fractional-order PID (OFFO-PID) algorithm is proposed to realize the vibration isolation and mitigation control of the precision platform with MRE devices. In the algorithm, the particle swarm optimization algorithm is used to optimize initial values of the fractional-order PID controller, and the fuzzy algorithm is used to update parameters of the fractional-order PID controller in real time, and the fractional-order PID controller is used to produce the control currents of the MRE devices. Numerical analysis for a platform with the MRE device is carried out to validate the effectiveness of the algorithm. Results show that the OFFO-PID algorithm can effectively reduce the dynamic responses of the precision platform system. Also, compared with the fuzzy fractional-order PID algorithm and the traditional PID algorithm, the OFFO-PID algorithm is better.

Inspired by the limb configuration of animals in their jumping and landing motions, a systematic investigation on the properties of a class of bio-inspired vertically asymmetric X-shaped (vaX) structures is carried out to explore the advantage of nonlinear characteristics in practical engineering. The nonlinear properties of two different vaX structures are studied under different constraint conditions. Formulations of the nonlinear vibration frequency and absolute displacement transmissibility of the structures are derived by the method of multiple scales. Considering practical conditions, three different constraints (i.e., (a) the same isolations height and assembling angle; (b) the same total rod length and assembling angle; (c) the same total rod length and isolation height) are summarized in this manuscript. Under these conditions, nonlinear properties including nonlinear vibration frequency, isolation performance and static stiffness are systematically discussed. Furthermore, the influences of the assembling pattern (i.e., normal and reverse assembling) on the isolation performance are investigated in detail. The results reveal that there exists rod-length ratio $$s_{1}$$ such that the nonlinear frequency ratio of the vaX-I vibration system is lowest; the natural frequency of the vaX-I structure is independent of the assembling pattern; however, compared with the normally assembled vaX-I structure, a lower resonant peak of the transmissibility can be obtained for the reverse-assembled structure, which suggests that the nonlinear damping of the vaX-I structure is affected by the assembling pattern. Experiments are carried out to verify the influence of the assembling pattern on the natural frequency and isolation performance of the vaX structures.

Viscoelastic dampers are a kind of energy-dissipation device with good damping performance. They are also extensively utilized in earthquake mitigation for structures in civil engineering. ...

Viscoelastic dampers are a kind of classical passive energy dissipation and vibration control devices which are widely utilized in engineering fields. The mechanical properties and energy dissipation capacity of the viscoelastic damper are significantly affected by ambient temperature. In this work, dynamic properties tests of the sandwich type viscoelastic damper at different environmental temperatures are carried out. The equivalent fractional Kelvin model which can characterize the mechanical behavior of the viscoelastic damper with varying frequencies and temperatures is introduced to describe the dynamic properties and energy dissipation capability of the sandwich viscoelastic damper. The self-heating phenomenon of the sandwich viscoelastic damper is studied with a numerical simulation, and the dynamic properties and energy dissipation variation of the viscoelastic damper with self-heating processes are also analyzed. The results show that the dynamic properties of the viscoelastic damper are significantly affected by temperature, excitation frequency and the internal self-generated heating.

A new kind of magnetorheological elastomer with the matrix of the bromobutyl rubber is developed. The magnetoviscoelasticity properties of the magnetorheological elastomer specimens are investigated with respect to different magnetic fields, displacement amplitudes, and frequencies under sinusoidal loadings. The experimental results show that the shear storage modulus and the loss factor of magnetorheological elastomers increase with the increasing magnetic field, excitation frequency, and the weight fraction of particles, but decrease with the increasing strain amplitude, and the magnetorheological elastomers have a high loss factor which can reach to 0.682. Then, a microphysical model based on the assumption of the chi-square distribution of the distance between adjacent ferromagnetic particles is proposed, which can eliminate the error generated by the assumption of the uniform distribution and describe the magnetorheological effect more exactly. Based on the proposed microphysical model, the magnetoviscoelasticity parameter model is modified to describe the dynamic properties of magnetorheological elastomers. It can be concluded from comparison between the numerical and experimental results that the modified magnetoviscoelasticity parameter model can describe the magnetorheological elastomer’s performance well.

Viscoelastic dampers are one of the most popular earthquake mitigation devices for building structures with a large number of applications in civil engineering. The seismic performance of viscoelastic dampers is greatly affected by viscoelastic materials. The present paper addresses the theoretical and experimental studies of the viscoelastic damper. The regular polyhedron chain network models for viscoelastic materials are proposed based on the molecular chain network microstructures and the temperature–frequency equivalent principle. Several dynamic property tests for the viscoelastic damper at different temperatures, frequencies, and displacements are carried out, and the proposed models are verified by comparing the numerical and experimental results. The comparisons show that the viscoelastic damper has perfect energy dissipation capacity, and the regular polyhedron chain network models can well describe the mechanical properties of the viscoelastic damper at different environmental temperatures and excitation frequencies.

Performance tests of magnetorheological (MR) dampers show that the hysteresis curves generally show an obvious force–lag phenomenon, which is due to the presence of trapped air in the working chamber of the damper. However, the force–lag phenomenon is barely considered in existing studies, and its influence on the seismic performance of MR damped structures is still unclear. In this paper, experimental and theoretical research have been carried out to analyze the force–lag phenomenon and its influence. Firstly, a specially designed MR damper was manufactured so that MR fluid can be poured into the damper successively for several times until the working chamber was filled, and performance tests were carried out correspondingly with different MR fluid perfusion densities (a parameter introduced in this paper to describe the volume fraction of MR fluid in the working chamber). The mechanical properties of the MR damper under different MR fluid perfusion densities were compared to reveal the influence of the force–lag phenomenon. Then, the effects of excitation properties on the force–lag phenomenon were discussed by comparing experiments results under different currents, frequencies and displacement amplitudes. Further, a force–lag mathematical model was proposed by considering the variation of the force-lag part with MR fluid perfusion density to reflect the force–lag phenomenon with different volume fractions of trapped air, and then verified based on the performance test data. Finally, numerical analysis of MR damped structures with different MR fluid perfusion densities was performed using the proposed force–lag mathematical model. Results show that the damping effect of MR control systems will be weaken due to the force–lag phenomenon, and with the increase of the MR fluid perfusion density, the seismic performance of MR damped structures will gradually improve.

The bridge stay cable, one of the most critical components in cable-stayed bridges, is vulnerable to vibrations owing to its low inherent damping capacity. Thus effective vibration control technology for bridge stay cables is extremely critical to safe operations of cable-stayed bridges. Several countermeasures have been presented and/or implemented to mitigate this vibration; however the passive method can only add a small amount of damping to the cables, excessive energy demand of active control devices severely limits its practicality, the semi-active control methods still have the drawbacks of complex state estimation module and a large amount of control algorithm calculation. This paper proposes a practical magnetorheological pseudo negative stiffness (MR-PNS) control system coupled with control strategy for bridge stay cables. The current reference point is introduced in the dynamic modeling of the MR-PNS control system to characterize the current control strategy. This paper investigates the adjustable of MR-PNS control system performance and energy consumption caused by different current strategies. Taking the vibration control of the Nanjing Second Yangtze River Bridge J20 cable as an example, the simulation results highlight the advantages of the MR-PNS control system that the failure area is small, the quasi-optimal area is wide, and it can still keep sort of vibration damping performance in the degenerate area. The model cable vibration control test proves the feasibility and efficiency of the single input MR-PNS bridge stay cables control method.

Magnetorheological (MR) damper is a semi-active control device designed by utilizing the instantaneous fluid-solid conversion characteristics of MR fluid, thus the microstructure of MR fluid fundamentally determines the mechanical properties of MR dampers. In order to study the influence of MR fluid microstructure on the macroscopic mechanical properties of MR dampers, a micro-macro mathematical model for MR dampers was proposed to describe the dynamic properties of MR dampers affected by the microstructure of MR fluid. Firstly, the micromodel of MR fluid was brought into classic quasi-static model and the double-Sigmoid model to propose a mathematical model, which considers the MR fluid microstructure by expressing the yield force parameter in the traditional double-Sigmoid model with the microstructure parameters of MR fluid. By analyzing the data of the performance test of a single-coil MR damper, the parameters of the proposed mathematical model were fitted. The proposed micro-macro model for MR dampers was verified by comparing the results calculated by this model with the performance test data. Based on the proposed micro-macro mathematical model, the nonlinear hysteretic curves with different MR fluid microstructure parameters can be numerically analyzed and compared. Finally, the influences of the volume fraction, size, and coating thickness of ferromagnetic particles on the mechanical properties of MR dampers were revealed and discussed. The research can provide guidance for the preparation and formulation optimization of high-performance MR fluid.

A unique bio-inspired multi-joint leg-like or limb-like vibration isolation structure is studied by mimicking the skeleton and joint structures of animal legs, and its advantage in passive vibration isolation is systematically investigated. This bio-inspired structure uses several small quadrilateral structures composed by short adjustable rods and a transverse spring to simulate the multi-articulation of animal legs and adopts long rods to simulate the skeleton. The equivalent static stiffness property, loading capacity and dynamic vibration isolation performance of the structure are systematically studied. It is shown that the nonlinear stiffness characteristics of the structure can lead to very excellent vibration isolation capability in the low-frequency band. Different from many existing quasi-zero-stiffness (QZS) isolators in the literature, this novel anti-vibration structure can demonstrate superior high static but low dynamic stiffness (HSLDS) property and thus excellent vibration isolation performance, subject to large vibration amplitude. Through adjusting proper structural parameters including the rod-length, assembly angle, spring stiffness and layer number according to the influence of the structural parameters on the nonlinear stiffness property, the new structure can have the optimal vibration isolation performance without sacrificing its loading capacity to meet actual requirements. Especially, the length of long rods which is used to simulate the skeleton can be adjusted to obtain better vibration isolation performance than adjusting other parameters, followed by the adjustment of the parameters of small quadrilateral structures. The analysis of the influence of structural parameters on the vibration isolation performance shows that the symmetry between different layers has an important role in maintaining the characteristic of the HSLDS. The comparison with other existing vibration isolation structures of the QZS property also indicates that, the new vibration isolation structure can have a better vibration isolation performance with relatively a smaller size of the overall structure. Experiments are successfully conducted and validated the beneficial nonlinear properties of the structure. This novelbio-inspired anti-vibration structure would have great advantages in practical engineering applications.

The magnetorheological (MR) fluid is a typical smart material, whose shear yield stress can be adjusted through changing the strength of external magnetic field, and the changing process only takes a few milliseconds. The MR fluid is composed of micro/nanometer ferromagnetic particles, carrier fluids, and some additives. Among them, the performance of ferromagnetic particles will mainly affect the sedimentation stability and the magnetic saturation of the MR fluid. Therefore, the ferromagnetic particles are expected to have characteristics of both low density and high magnetism. In this paper, the multi-walled carbon nanotubes (MWNTs) were adopted to coat on the carbonyl iron (CI) particles with grafting technology using ultrasonication and mechanical stirring. The coated CI particles with perfect core-shell structure were developed and the influence of the dosages of grafting agent and MWNTs were tested. And then, MR fluids with CI particles coated with MWNTs were established and the coating effect was studied through surface topography particle density, and magnetic properties of composite magnetic particles and stability tests of the prepared MR fluids. The results showed that although the magnetic saturation of the prepared MR fluids with CI particles coated with MWNTs would reduce slightly, the particles density and the adsorption force between the particles were decreased effectively, which are both advantageous to the improvement of the sedimentation stability of MR fluids.

In this paper the physical and dynamic mechanical property tests of magnetorheological elastomers (MREs) are reported. Two kinds of MREs with different matrices, about 12 samples in total, are fabricated by mixing carbonyl iron powder and additives, and cured by using a constant magnetic field. The physical and dynamic viscoelastic properties of these MRE specimens are evaluated with respect to different magnetic fields, displacement amplitudes, and frequencies. The experimental results demonstrate that MREs have variable stiffness and the loss factor of the samples with bromobutyl rubber is high, which shows a good damping property. The proposed magnetoviscoelasticity parameter model is then verified by comparing the experimental and numerical results, which demonstrate that the magnetoviscoelasticity parameter model can describe the MRE performance well.

Tribological properties of ceramic cutting tool materials in contact with wood based materials were studied in this paper by examining how Al2O3-ceramics and Si3N4-ceramics behave in dry sliding experiment in contact with wood-based materials and by comparing their behavior with tungsten carbide material at the same time. It had been found that the ceramics exhibited much better tribological properties than tungsten carbide material, and Si3N4-ceramic performed better than Al2O3-ceramics. The Al2O3-ceramics with an addition of ZrO2 had better tribological performance than the common Al2O3-ceramics in contact with wood-based materials. The tungsten carbide had better tribological performance than ceramics in tribological contact with wood flour/PE material. A well-marked difference occurred in various cutting materials/MDF frictional pair, but the differences in various cutting materials/PB frictional pair were insignificant. An increase of the normal force didn’t result in any significant decrease of the friction coefficient. An addition of ZrO2 in the Al2O3-ceramics could inhabit corrosive wear.

The magnetic particles coated with the carbon are used in the magneto-rheological fluids (MRFs) and the coat-like structure slow down the sedimentation of MRFs. Meanwhile, after the performance tests, the new MRF has the low viscosity and good ability of the recovery. These characters have more advantages in the application fields. Based on the prepared MRF, a shearing model that considers the interaction force between the adjacent chains was presented. By applying the proposed model, some conclusions are reached. The volume ratio of the magnetic particles has an important effect on the yield stress of the MRFs. The shear strain where the maximum shear stress happened has something to do with the volume ratio of the magnetic particles.

By using parallel process of photocatalysis-biological contact oxidation, a research on the pretreatment effect of micro-polluted raw water was conducted. The result indicates that the changes of HRT and the initial concentration take significant impact on the removal of NH3-N. 60min is the best residence time for the pretreatment. Once the thickness of composite media is 120mm, the removal efficiency of CODMn may reach as much as 15.55%, while the average removal efficiency of turbidity is 20%. Since the nitration reaction consumes certain amount of alkalinity, the pH value of outlet water is lower than inlet water. When employing parallel process, biological oxidation and photocatalysis are performed and finished in the same reactor simultaneously, conducing to maintaining a moderate level of the removal of CODMn and NH3-N. All these are of reference value for its application in practical engineering projects.

Magnetorheological elastomers (MRE) have been synthesized on the basis of a silicon compound and a mixture of carbonyl iron particles of sizes 3–5 and 40–80 μm. Their viscoelastic properties have been studied by dynamic shear oscillations of various amplitudes on a stress controlled rheometer. The magnetic response of the obtained materials has been examined in a magnetic field applied perpendicular to the shear plane. It has been shown that under applied magnetic field both the storage G′ and loss G″ moduli became strain-dependent. The values of G′ and G″ decrease with strain, while their ratio (the loss factor), G″/G′, growths with strain. The higher magnetic field is the more pronounced the strain dependence is. At small strain (up to 1%) MRE demonstrate a giant (more than 10 times) increase of the moduli. Some features of hysteretic behavior of MRE under simultaneously applied magnetic field and external mechanical force have been elucidated. Temperature has a negligible effect on viscoelastic properties and stability of the developed MRE. A damper on the basis of MRE has been designed and its properties have been examined.

Both experimental and modeling studies of magnetic field induced viscoelastic properties of magnetorheological (MR) elastomers under different loading cases are discussed. Anisotropic MR elastomer (MRE) samples with different concentrations of carbonyl iron powder, natural rubber and additives are fabricated and four MRE vibration mitigation devices are manufactured to investigate the dynamic viscoelastic properties of MREs under varying magnetic fields, displacement amplitudes and frequencies in the shear mode. The characteristics of the dynamic properties of the MRE devices are obtained in terms of the experimentally determined shear storage modulus and loss factor. These results demonstrate that the MREs exhibit variable stiffness and damping properties. Based on the studies of properties of viscoelastic materials and the experimental results of MREs, a parameter model is proposed to describe MRE performances. The four parameters under various working conditions, such as magnetic field, displacement amplitude and frequency, are identified by using the Matlab optimization algorithm. Comparisons between experimental and numerical results are discussed, and the results show that the proposed parameter model can describe the performances of MRE devices very well.