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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...

Current numerical methods cannot simulate well three-dimensional (3D) fracture process of solids. In order to study 3D fracture process of brittle-like materials and improve crack growth path prediction accuracy, a method is developed based on continuum damage mechanics and finite element method. In the developed method, damage is computed by homogenizing stress or strain in the preset characteristic field for reducing the spurious mesh sensitivity. Meanwhile, an additional procedure is used to consider the unstable and competing fracture process, which can be used to consider stress redistribution due to local damage evolution during the fracture process simulation. In addition, a damage model of concrete is also developed and used to describe material damage. Finally, 3D fracture process of two numerical examples, were simulated and compared with the experimental results by using the developed method. The 3D crack growth path and macroscopic mechanical behaviors can be predicted by the developed method coupled with a damage model. From the comparison, the effectiveness and modeling capability of the developed method are verified, which can be used to study 3D fracture mechanisms of concrete-like materials.

To improve the efficiency of conventional isolation trench and lighten the impact of the excavation on neighbor buildings, a novel high damping isolation trench is proposed. The viscoelastic braces equipped in the high damping isolation trench can dissipate the energy of ground-borne vibration while providing supporting force to ensure the stability of the soil on both sides. According to two actual ancient buildings, two types of high damping isolation trenchs with the plane shape of U and L are designed to solve the potential damages caused by long-term train-induced vibration. First, three-dimensional finite/infinite models based on these two buildings are established, respectively. Then, the energy dissipation characteristics are obtained by experiments. Through calculation, the control effects of the high damping isolation trenchs for these two buildings are investigated. The results indicate that the viscoelastic braces possess high energy dissipation capacity. After setting the high damping isolation trenchs around the structures, even at a small excavation depth, the acceleration and velocity responses of the two buildings are reduced significantly. Furthermore, the selected U-shaped and L-shaped trenches also show superiority compared with the conventional linear-shaped trench in this project.

The traditional preparation processes for magnetorheological (MR) fluids are complicated and time-consuming, and cannot guarantee the performance of the prepared material, especially for the MR fluid with mixed coated particles. In this study, an improved drying-free preparation method of MR fluids was proposed, which adopts the magnetic separation technology to replace the traditional drying process, and an integrated preparation device for preparing MR fluids was designed on this basis to realize high efficiency and automation. The MR fluid with multiwalled carbon nanotube/graphene oxide-coated carbonyl iron particles was prepared using the designed device, and the test results showed that the drying-free preparation process can save 1/3 of the original preparation time. Then, the zero-field viscosity, yield shear stress and sedimentation rate of the prepared MR fluid were tested and compared with those prepared by the manual preparation methods. Under appropriate proportion of ingredients, the MR fluid prepared by the drying-free process has higher yield shear stress and better sedimentation stability. Therefore, the drying-free preparation process and the integrated preparation device proposed in this study are not only efficient and automated, but also can improve the performance of MR fluids.

Magnetorheological (MR) fluid is a typical intelligent material which is widely adopted in the mitigation of civil engineering structures, and it is normally composed of nano-sized or micro-sized iron particles, carrier fluids and additives. Because of the complexity of its composition, it is one of the research hotspot to propose a micromechanical model which can effectively describe the micromorphological transformation as well as characteristics of MR fluids. In this study, a single-double chains micromechanical model of MR fluids is proposed by taking into consideration of the influence of volume fraction and magnetic induction on the microstructure evolution of MR fluids based on the coupled field as well as magnetic dipole theory. Additionally, the shear yield stress test of the self-prepared MR fluids with multi-wall carbon nanotubes(MWCNTs) and graphene oxide (GO) composites coated ferromagnetic particles is carried out by MCR302 rotational rheometer and the results have been compared with the theoretical values of the single-double chains micromechanical model to verify the effectiveness and accuracy of the proposed model.

Because shock absorbers are an important component of high-rise buildings, it is essential to be able to detect damage to them. Viscoelastic (VE) dampers, as a common shock absorber, direct...

Experimental results show that mechanical behaviors of viscoelastic dampers are greatly affected by ambient temperature. Neglecting the ambient temperature effect will lead to an inaccurate seismic evaluation on viscoelastically damped structures. This study investigates the ambient temperature effect on the seismic performance of viscoelastically damped structures. An efficient algorithm is proposed to solve the seismic response of viscoelastically damped structures at different ambient temperatures based on the time–temperature correspondence. Numerical simulations of a ten-story viscoelastically damped steel frame under historical earthquakes are presented to illustrate the ambient temperature effect on the seismic performance. The results show that the natural frequency decreases with the increase in ambient temperature, whereas the damping ratio change with ambient temperature greatly depends on the viscoelastic damper properties. The seismic displacement reduction, in general, decreases with the increase in ambient temperature. The seismic acceleration reduction with ambient temperature is affected by the viscoelastic damper properties, structural parameters, and earthquakes together.

Magnetorheological damper is a typical semi-active control device. Its output damping force varies with the internal magnetic field, which is a key factor affecting the dynamic performance of the magnetorheological dampers. Existing studies about the magnetic field of magnetorheological dampers are limited to theoretical analysis; thus, this study aims to experimentally explore the complicated magnetic field distribution inside the magnetorheological dampers with multiple coils. First, the magnetic circuit of a three-coil magnetorheological damper was theoretically analyzed and designed, and the finite element model of the three-coil magnetorheological damper was set up to calculate the magnetic induction intensities of the damping gaps in different currents and numbers of coil turns. A three-coil magnetorheological damper embedded with a Hall sensor was then manufactured based on the theoretical and finite element analysis, and internal magnetic field tests under different conditions were carried out to obtain the actual magnetic induction intensities. At last, the magnetic field coupling model of the three-coil magnetorheological damper was proposed by introducing a coupling coefficient to describe the complex magnetic field distribution due to the strong coupling effect of the three coils, and the results calculated by the proposed model agreed well with the finite element analysis and magnetic field test data. The proposed model lays a foundation for the optimal design of the magnetic circuit and the mathematical model of multi-coil magnetorheological dampers.

Asymmetric structures experience torsional effects when subjected to seismic excitation. The resulting rotation will further aggravate the damage of the structure. A mathematical model is developed to study the translation and rotation response of the structure during seismic excitation. The motion equations of the structures which cover the translation and rotation are obtained by the theoretical derivations and calculations. Through the simulated computation, the translation and rotation response of the structure with the uncontrolled system, the tuned mass damper control system, and active tuned mass damper control system using linear quadratic regulator algorithm are compared to verify the effectiveness of the proposed active control system. In addition, the linear quadratic regulator and fuzzy neural network algorithm are used to the active tuned mass damper control system as a contrast group to study the response of the structure with different active control method. It can be concluded that the structure response has a significant reduction by using active tuned mass damper control system. Furthermore, it can be also found that fuzzy neural network algorithm can replace the linear quadratic regulator algorithm in an active control system. Because fuzzy neural network algorithm can control the process on an uncertain mathematical model, it has more potential in practical applications than the linear quadratic regulator control method.

At present the vibration control of stay cable suffers from low damping effectiveness in single mode vibration caused by the limitation of damper installation position as well as the poor modal compatibility, that is, a rapid degradation performance when the actual mode deviates from the designed optimal mode. In this paper, one practical semi-active magnetorheological (MR) damper based control solution is proposed to address the problems faced in multi-modal vibration control of stay cables. The semi-active pseudo negative stiffness (PNS) control strategy takes full account of the MR damper’s mechanical characteristics and the demands of the stay cable vibration control. Compared with the linear equivalent model, the proposed time-varying model exhibits more details of the damping force and the nonlinear response of the damped stay cable, which shows its essential role in the optimal design of MR-PNS scheme. Then the optimal design method of MR-PNS multi-modal vibration control for stay cable is summarized by taking the first three modes vibration control of the J20 cable in Nanjing Baguazhou Yangtze River Bridge as simulation examples. The simulations of cross-modal, multi-modal and wind-induced vibration cases are conducted respectively, while the results show that the optimal designed multi-modal MR-PNS scheme can simultaneously exceed the passive maximum modal damping ratio within first three modes. The advantages of the proposed MR-PNS method in high damping efficiency and modal compatibility could be verified by comparing with the passive multi-modal damping solution.

Bistable and multistable structures with snap-through behavior can achieve nonlinear and negative stiffness based on their geometric nonlinearity in elastic deformation. Traditionally, loading capacity and stiffness of this kind of structure tend to be relatively low, a drawback that can potentially be overcome by making section bistable beams varying along its length. However, there currently lacks a systematic evaluation on influences of the sectional alignment on its mechanical performance. Based on the chained constrained beam model, a simplified method for calculating the structure is derived in this paper. The method is validated by a series of tests. Using the method, a systematic parametric study is performed and optimization studies are conducted to establish the best achievable mechanical behavior of the bistable structure subjected to different design limitations. Influences of the stiffness of the lateral restraints on performance of the structure are also investigated. At last, a structure based on the bistable beams connected in parallel were designed using the proposed methodology and tested.

To simulate the crack growth and study the catastrophic fracture mechanisms of metal films, a computational methodology is developed to simulate the failure process from damage initiation to crack growth and eventually to rupture. In the computational methodology, a procedure is developed based on beam lattice model for considering the coupling interactions among damage and crack evolution. To verify the effectiveness of the developed computational methodology, fracture process of two copper film specimens were simulated and compared with the corresponding experimental results. The results show that the developed methodology is effective, and can be used to simulate the catastrophic fracture process of metal films. From the simulation results, we can find out that the fracture of metal films with initial flaws belongs to brittle fracture, and the regular lattice model can affect the crack path prediction, and random and irregular lattice model is more suitable to simulate crack growth in the developed computational methodology.

The purpose of this paper is to investigate the contribution of viscoelastic material (VEM) to the control performance of the viscoelastic tuned mass damper (VTMD). Firstly, the equivalent fractional derivation Kelvin model is used to describe the frequency dependence of viscoelasticity in VTMD, and an index is proposed to characterize the level of frequency dependence. Then the effects of the high loss factor of VEM and frequency dependence of viscoelasticity on the effectiveness and robustness of VTMD control are analyzed by numerical examples. At last, a design strategy for VTMD is proposed to select the type of VEM and optimize its stiffness contribution. The results show that the frequency dependence of shear storage modulus of VEM is beneficial to further reduce the dynamic response of the primary structure equipped with VTMD, and the loss factor of VEM determines the optimum frequency ratio and control effect of VTMD. Compared to the conventional tuned mass damper, VTMD has a better robustness for the positive error of the natural frequency of VTMD but has a worse robustness for the negative error. The frequency dependence of shear storage modulus of VEM is beneficial to the robustness of VTMD for both the positive and negative errors of the natural frequency of the primary structure. The VEM with a strong frequency dependence of shear storage modulus is the ideal VEM for VTMD, and the proposed design strategy can deal with the trade-off between the control effectiveness and control robustness of VTMD.

Viscoelastic (VE) dampers are a kind of effective passive vibration control device and widely used to attenuate structural vibration. In this article, experimental study and multiscale modeling analysis on the VE damper for reducing wind-excited vibration are carried out. First, an experimental study on VE damper is conducted to reveal the dynamic properties of VE damper. The experimental results show that the dynamic properties of VE material are influenced by excitation frequency and insignificantly affected by displacement amplitude, and the VE material has good energy dissipation capacity. Second, the damping mechanism of VE damper is analyzed from micro-perspectives by considering the influence of cross-linked and free molecular chain networks. Then, a novel type spherical chain network model based on the chain network microstructure is proposed. The proposed model is verified by comparing the experimental data and the mathematical results, which indicates that the proposed model can accurately describe the dynamic properties of VE damper affected by different temperatures, frequencies, and displacements.

Base isolation is a powerful technique to prevent damage in low- and medium-rise structures during an earthquake. Nowadays, the extensive use of high-damping viscoelastic (VE) materials in ...

In order to overcome serious utility tunnel fires and minimize economic loss, it is essential to establish an effective and practical method for finding the fire source. An adaptive Particle Swarm Optimization (PSO) algorithm was proposed for fire source identification of utility tunnel fires, whose inertia weight and learning factors were adjusted dynamically. In comparison with traditional fire detection methods, the proposed algorithm is immune to the specific environment and complicated fire propagation mechanisms, the fire source location can be identified only based on several temperature values. The proposed algorithm was applied in both numerical and experimental scenarios. The results showed that the adaptive algorithm showed greater global searchability in the early exploration, and stronger local searchability in the later exploration compared with the basic one, the improvement ratio of convergence performance could achieve 50%. Additionally, all of the cases demonstrated that the fire source location can be identified by the proposed algorithm with good accuracy. Critically, the spatial temperature distribution of the whole utility tunnel was obtained based on the fire source location and the attenuation coefficient. The reasonable results indicate that the proposed algorithm can provide a reference for fire protection and intervention in the utility tunnel.

This paper addresses a physical damage model and continuum damage-based fracture simulation procedure for simulating crack initiation, growth and cracks coalescence of quasi-brittle geomaterials. The model is proposed by using the principle of minimum dissipative energy combining with Drucker-Prager criterion, in which every parameter of the damage model has clear physical meaning. The procedure coupled with the damage model can be used to simulate competitive fracture process based on finite element method, which is implemented by using the secondary developing tool of ANSYS software. Two benchmark tests of the two pre-cracked rock-like disk specimens were carried. The predicted crack growth paths matched well with the corresponding experimental results. Thus the fracture simulation of dog-bone specimens with different sizes were carried to consider the scale effect, which support the effectiveness and ability of the developed procedure and damage model.

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.

A new viscoelastic micro-vibration isolation and mitigation platform is proposed to reduce disturbances generated by flywheels on board spacecraft. Firstly, property tests on the high-damping viscoelastic material used in the micro-vibration isolation and mitigation element are conducted. Experimental results show that the developed viscoelastic material has better energy dissipation capability under micro-vibration conditions. A mathematic model is employed to describe the dynamic properties of the high-damping viscoelastic material and is used to model the isolation and mitigation element. Secondly, a viscoelastic micro-vibration isolation and mitigation platform, which consists of four elements, is proposed and the analytical model of the coupled system that consists of the platform with flywheel is established. Finally, the isolation and mitigation performances of this micro-vibration isolation and mitigation platform are analyzed and discussed. The results show that the isolation and mitigation platform can effectively reduce the micro-vibration disturbances induced by the flywheel.

1-Butyl 3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMI)-modified multiwalled carbon nanotubes (MWCNTs) were used as nanofillers for the hydrogenated carboxylated nitrile–butadiene rubber/hydrogenated nitrile–butadiene rubber (HXNBR/HNBR) blends. The multifunctional properties of rubber nanocomposites with various filler loadings were investigated. It was found that in the presence of BMI-MWCNTs, the mechanical strength, dielectric properties, electrical and thermal conductivities of HXNBR/HNBR were significantly improved due to the better dispersibility as well as the intrinsic reinforcement effect of MWCNTs. Particularly, in comparison with unfilled rubber blend, the electrical conductivity of BMI-MWCNTs-filled HXNBR/HNBR composites exhibited three orders of magnitude enhancement with a lower electrical percolation threshold. The tensile strength and thermal conductivity of composites filled with 5 phr (parts per hundred rubber) BMI-MWCNTs increased by 52 and 23%, respectively. In addition, the polarizability of composites was also intensified under the applied electric field, which resulted in remarkable dielectric relaxation compared to neat rubber. Our experimental data have indicated that BMI-MWCNTs can be used as a promising candidate for fabricating multifunctional HXNBR/HNBR nanocomposites.

Viscoelastic materials are a kind of representative passive vibration control materials with many applications in civil engineering for earthquake mitigation in building structures, and these materials often serve in a thermo-elastic coupling environment. In this work, a one-dimensional magneto-thermoviscoelastic problem of a single-layer viscoelastic plate is investigated with memory-dependent derivative and nonlocal effect in the context of generalized thermo-elasticity. The plate is placed in a magnetic field, and the upper surface is subjected to a thermal shock. The governing equations for the single-layer plate are formulated considering the time delay and the kernel function of the memory-dependent derivative, nonlocal effect, temperature-dependent properties, and magnetic field. The Laplace transform and its numerical inversion are employed to solve this problem. The nondimensional temperature, displacement, and stress are calculated and presented graphically. Based on the numerical results, the influence of time delay and kernel function of the memory-dependent derivative, nonlocal effect parameters, temperature-dependent properties, and magnetic field parameters on the distributions of the nondimensional temperature, displacement, and stress are discussed.

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.

A numerical method is developed to simulate effectively meso-scopic damage evolution of concrete subjected to cyclic fatigue loading based on considering its heterogeneous material constituents. In the developed method, a fatigue damage evolution gradient controlled procedure is developed to speed up fatigue damage simulation in a reasonable way by using the developed damage model. In the procedure, the block cycle jump strategy is used and the maximal fatigue damage accumulation for each block cyclic loading is controlled to be less than the pre-set value based on the condition of efficiency and precision. In addition, a heterogeneous concrete modeling strategy is developed and used to consider heterogeneous material constituents with lower computational cost, in which material parameters are assumed to obey some kinds of probability distribution such as Gaussian distribution. A representative numerical example supports the effectiveness of the developed numerical method, which illustrates its ability to simulate well fatigue damage evolution of heterogeneous concrete. From simulation results obtained from different finite element models with coarse and fine mesh. We can also find that fatigue analysis results are insensitive to gird mesh by using the developed numerical method.

Mechanical property and durability of timber members is significantly affected by their surface moisture emissivity which determines the rate they exchange the moisture with the surrounding air. The surface moisture emissivity depends on various parameters including the air flow rate, the temperature and the surface treatment. However, there currently lacks a suitable method for measuring it in the actual working environment of the timber structures. This paper proposes such a method which can identify the surface moisture emissivity factor for timber members with different kinds of surface treatment in their unsteady moisture transfer process. The method is based on Bayesian updating of the numerical model of moisture transfer process of the wood based on the overall weight change. The numerical model considers coupled transfer of the vapour and the bound water. Influences of the sorption hysteresis were also included. Using the method, moisture emissivity factor of different kinds of timber surfaces can be measured by weighting their small-sized samples exposed to ambient climate. Steady moisture transfer process, controlled temperature and RH environment, or the information of the moisture gradient in the samples are not required. Using the method, surface moisture emissivity factor of a pine wood was determined without and with different kinds of surface paint. The measured factor was validated by additional experimental data.

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.

Hybrid simulation is an advanced structural dynamic experimental method that combines experimental physical models with analytical numerical models. It has increasingly been recognised as a powerful methodology to evaluate structural nonlinear components and systems under realistic operating conditions. One of the barriers for this advanced testing is the lack of flexible software for hybrid simulation using heterogeneous experimental equipment. In this study, an electrodynamic fatigue test machine is made and a MATLAB program is developed for hybrid simulation. Compared with the servo-hydraulic system, electrodynamic fatigue test machine has the advantages of small volume, easy operation and fast response. A hybrid simulation is conducted to verify the flexibility and capability of the whole system whose experimental substructure is one spring brace and numerical substructure is a two-storey steel frame structure. Experimental and numerical results show the feasibility and applicability of the wh...

A facile non-covalent surface treatment method is reported in this paper to modify graphene oxide (GO) sheets with the assistance of polyvinylpyrrolidone (PVP). The PVP-modified GO (PGO) was further adopted to fabricate PGO/styrene–butadiene rubber (SBR) nano-composites through the latex compounding method. The properties of PGO were carefully investigated and interaction between GO and PVP molecules was confirmed. The mechanical properties, dynamic mechanical properties, thermal stability, thermal conductivity as well as swelling properties of the PGO/SBR nano-composites were thoroughly studied. It was confirmed that PVP molecules could have strong interaction with GO via hydrogen bond; thus, the PGO significantly improved the strength of SBR matrix, e.g., 517 and 387 % increase in tensile strength and tear strength, respectively, with the presence of only 5 phr (parts per hundred rubber) PGO in the nano-composite. The presence of PGO had also greatly reduced the glass transition temperature (T g) and enhanced the storage modulus of SBR matrix in the nano-composites. Meanwhile, the maximum heat decomposition temperature (T max) was increased by 23.6 °C; equilibrium solvent uptake in toluene was reduced by 41 % and thermal conductivity was increased by 30 %. All the observations indicated that PVP modification of GO can achieve excellent exfoliation and dispersion of GO in the SBR matrix. These findings were further supported by X-ray diffraction and scanning electron microscopy measurements.

Magnetorheological (MR) fluid is a typical intelligent material which is widely adopted in the mitigation of civil engineering structures, and it is normally composed of nano-sized or micro-sized iron particles, carrier fluids and additives. In the study, ferromagnetic particles coated with multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO) composites were prepared with grafting technology and the influence concerning ratio of MWCNTs, GO, grafting agent as well as carbonyl iron (CI) particles was studied to select the composite ferromagnetic particles which have the best effects of coating through surface topography analysis. In addition, the MWCNTs/GO composites coated CI particles and surfactants-modified CI particles were combined together to prepare a series of MR fluids with different ratio of the two compound ferromagnetic particles, volume fraction of total ferromagnetic particles and additives by the control variable method and the influence of the factors on the performances of MR fluids was investigated through sedimentation stability, re-dispersion, zero field viscosity and shear yield stress tests. The test results presented that the introduction of MWCNTs/GO composites coated CI particles was beneficial to the improvement of stability with sedimentation rate lower than 6%.

A physical damage model based on minimum Lemaitre's damage strain energy release rate is developed to describe quasi-brittle materials' softening. A modified finite element procedure together with the developed damage model is used to simulate the fracture process of quasi-brittle specimens. In the developed procedure, damage is only updated in the most dangerous element at each iteration, and mesh dependency can be reduced based on this way. Two representative numerical examples support the effectiveness of the developed damage model and procedure, which illustrate their ability to objectively simulate the mixed-mode failure process of quasi-brittle materials due to tension, compression and shear. In addition, we found that the simulation results obtained from the modified finite element procedure are insensitive to grid mesh.

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.

This research addresses the dynamic compressive properties of flax fibre reinforced polymer (FFRP) and glass fibre reinforced polymer (GFRP) confined concrete under impact loadings. The investigations were performed by conducting impact tests using a high-speed servo-hydraulic machine, with the impact-induced strain rates ranging from 0.2 s−1 to 30 s−1. Plain concrete (PC), FFRP-PC, and GFRP-PC specimens were tested. The influences of FRP confinement and strain rate on compressive strength, stress and strain time histories were studied. The failure processes of the specimens were analysed via evaluating the high-speed camera photographs. The empirical relationship between the corresponding dynamic increase factor (DIF) of compressive strength and strain rate for PC, FFRP-PC and GFRP-PC were proposed based on experimental data. Experimental results of FFRP-PC and GFRP-PC specimens were compared to assess the confinement effectiveness of the FRP.

Recently, magnetorheological elastomer–based vibration control devices have attracted increasing attention due to their field dependence of stiffness characteristics. It is crucial to devel...

Magnetorheological (MR) fluids are suspensions of microparticles or nanoparticles dispersed in carrier fluids, which contain iron particles, carrier fluids and additives. In this study, a n...

Multilayered piezoelectric structures have special applications for vibration control, and they often serve in a thermoelastic coupling environment. In this work, the fractional-order generalized thermoelasticity theory is used to investigate the dynamic thermal and elastic behavior of a bilayer piezoelectric–thermoelastic plate with temperature-dependent properties. The thermal contact resistance is implemented to describe the interfacial thermal wave propagation. The governing equations for the bilayer piezoelectric–thermoelastic plate with temperature-dependent properties are formulated and then solved by means of Laplace transformation and Riemann-sum approximation. The distributions of the nondimensional temperature, displacement, and stress are obtained and illustrated graphically. According to the numerical results, the effects of the thermal contact resistance, the ratio of the material properties between different layers, the temperature-dependent properties, and the fractional-order parameters on the distributions of the considered quantities are revealed in different cases and some remarkable conclusions are obtained. The investigation helps gain insights into the optimal design of actuators, sensors, which are made of piezoelectric materials.

In this paper, tests on viscoelastic (VE) dampers are carried out, and the results indicate that VE dampers have high energy dissipation capacity and excellent anti-fatigue properties. To clarify the mechanical properties of VE dampers, a new mathematical model, named the equivalent fractional Kelvin model, which considers temperature and frequency effects simultaneously, is proposed. The numerical results using this model are in good agreement with experimental results. Then, through analysis on a five-story reinforced concrete frame structure with and without VE dampers, it is found that the seismic responses of the structure with VE dampers are significantly reduced and VE dampers have high energy dissipation capacity.

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.