Ning Ma

To resolve the disturbance issues of complex vibrations in the environment on precision equipment, a smart variable-stiffness isolator based on bidirectional variable-modulus magnetorheological elastomers (B-MREs) is designed in this study. Considering the stability, lateral deformation, and vertical bearing capacity of the proposed isolator, the parametric design of its laminated structure and overall configuration is finalized. Based on magnetic circuit calculations and finite element electromagnetic field simulation analysis, the validity of the magnetic flux distribution and the structural design within the proposed isolator is verified. A test platform is set up to conduct dynamic performance tests on the proposed isolator, with a view to investigating the effects of current, frequency, and displacement amplitude on its equivalent stiffness. A nonlinear dynamic model is established to characterize the mechanical performance of the proposed isolator, and the fitted results are compared with the experimental data. The results demonstrate that the proposed isolator possesses a significant capacity for bidirectional variable-stiffness regulation in both positive and negative directions. The numerical results of the improved dynamic model are in good agreement with the experimental data under various working conditions, which proves that the model can reliably describe the nonlinear hysteretic mechanical properties of the proposed isolator.

To improve the wide-frequency vibration control capability of semi-active vibration isolators, the bidirectional variable modulus performance of hard magnetic magnetorheological elastomers (H-MRE) is crucial. To further enhance the characteristics of H-MRE, various technical solutions have been implemented in recent years, including filling H-MRE with pre-magnetized hard magnetic particles and doping soft magnetic particles into H-MRE. However, existing studies have faced issues such as particle agglomeration and complex preparation processes. In response to the contradiction between the complexity of the H-MRE preparation process and performance improvement in existing research, this study improves MRE performance by optimizing the hard magnetic particles and their distribution in H-MRE. By replacing traditional hard magnetic particles with magnetocrystalline anisotropic NdFeB particles, which exhibit better magnetic properties such as remanent magnetization, coercivity and saturation magnetization. The study systematically investigates the mechanism by which particle distribution influences H-MRE performance. Experimental results show that while enhancing the amplitude of positive modulus changes, the reverse modulus change amplitude of H-MRE is increased to 23.3%. This study lays an important foundation for the application of H-MRE in vibration control fields.

Prior research has predominantly focused on traditional electrorheological (ER) effects while overlooking the transformative potential of induced dipoles in enhancing the overall performance of ER materials. In this study, we introduced a novel type of ER elastomer called induced dipole-dominated ER elastomer (ID-ERE). Through high-energy ball milling (HEBM) of the filler particles, the oxygen vacancies were produced within the particles that acted as local charge centers. In the presence of an external electric field (E), these oxygen vacancies induced the dipoles with significant dipole moments, thus amplifying the local electric field E_L within the particle gaps. The powerful interactions of these dipoles significantly improved the overall performance of elastomer; the phenomenon referred to as the ID-ER effect. The viscoelastic results showed that ID-EREs have high field-induced storage modulus (G’ = 395.7 kPa), a significant increment in storage modulus (ΔG’ = 270.5 kPa) and high relative ER effect (ΔG’/G0 = 217.2%) at 3 kV mm⁻¹. Additionally, after testing ID-EREs viscoelastic properties, it was discovered that excessive powder content leads to a decline in the elastomer’s performance. The results showed that ID-ERE’s viscoelastic, mechanical, dielectric, and overall efficiency is finer than the control ER elastomer (C-ERE) having unmilled TiO₂ particles. Besides, the preparation method is straightforward, easily replicated, scalable, and cost effective. Thus, these ID-EREs should be a new generation of elastomer with the potential to be used in various automotive, robotics, construction, and electroactive actuators industries.

Ferrofluid (FF) has attracted more and more attention due to its tunable rheological properties, in which the microstructure under a magnetic field plays an important role in these properties. In this study, an innovative coarse-grained (CG) model of FF is presented for the first time to capture the microstructure evolution of FF at the nanoscale. The potential functions of carrier liquid for FF CG models are obtained by the iterative Boltzmann inversion method, and the CG nonbonded interaction between the magnetic particles (MPs) is obtained via the strain energy conservation. Then, CG molecular dynamics (CGMD) simulations are used to study the microstructure evolutions of FF under different magnetic fields. Notably, we demonstrate the existence of a carrier liquid adsorption layer on the MPs surface, and its thickness is calculated. The staggered arrangement style of MPs in the chains is also revealed by the CGMD method. The present FF CG model has fully considered the carrier liquid molecular structure and interaction with the MPs, and the CGMD is used to solve the problem that classical molecular dynamics cannot simulate the microstructure of FF, making the simulation results more in line with the actual situation.

Fe–Co alloys exhibit an excellent saturation magnetization, which makes them become a potential candidate for the high property magnetic particles in magnetorheological fluids (MRFs). How to decrease their coercivity and residual magnetization without sacrificing the saturation magnetization is a crucial problem to be solved. In this study, Fe–Co nanoparticles were prepared by DC arc discharge and further disposed through low temperature annealing in Ar atmosphere. The successful synthesis of Fe–Co nanoparticles was proved by x-ray diffraction and EDS. The vibrating sample magnetometer results revealed that the prepared Fe–Co nanoparticles had a saturation magnetization of 208 emu g⁻¹, while the coercivity and remanent magnetization were 58 Oe and 5.8 emu g⁻¹, respectively. The MR properties of Fe–Co nanoparticles based MRFs (FeCoNP-MRFs) with 10% particles by volume fraction were systematically investigated. The FeCoNP-MRFs showed up to 4.61 kPa dynamic shear stress at 436 kA m⁻¹ magnetic field and an excellent reversibility. The MR properties of FeCoNP-MRFs were fitted well by Bingham and power law model, and described by Seo-Seo and Casson fluid model. Meanwhile, the sedimentation ratio of FeCoNP-MRFs was still 87.3% after 72 h, indicating an excellent sedimentation stability.

Buckling-restrained brace (BRB) is a dual-function device that improves the seismic resistance and energy-dissipation capacity of structures in earthquake engineering. To achieve the expected performance under severe ground motions, BRB is usually designed to remain elastic under mild earthquakes, leading to the increased seismic forces and insignificant vibration-reduction effect on the structures at this stage. This study extends the concept of adaptive passive-control of structures by proposing a novel frictional-yielding compounded BRB (FBRB). FBRB is fabricated by connecting the BRB steel casing and end plates with the friction dampers (FDs) in such a way that the BRB steel core and FDs undergo compatible deformation. In this way, FD dissipates seismic energy under mild earthquakes, while FD together with the BRB core dissipates energy under severe ground motions, resulting in an efficient self-adaptive vibration-reduction mechanism. The proposed FBRB construction was experimentally validated by carrying out the reversed-cyclic test, and the result indicated reliable connection with stable hysteretic behavior. Subsequently, the FBRB-equipped frame was proposed and studied which adopted FBRB as the energy-dissipative devices. A parametric design method was developed to determine the FBRB parameters with which the maximum elastic drift of the system could be reduced to the code-allowable value. The approach was implemented on a 48-story mega FBRB-equipped steel frame as the case study. The seismic behavior of the FBRB-equipped case structure was compared with that of the BRB-equipped system, and critically evaluated by carrying out the nonlinear time-history analyses. Results revealed that FBRB compensated for the conventional BRB in terms of inadequate energy dissipation under mild earthquakes and, meanwhile, was more efficient than the conventional BRB in reducing the lateral drifts under severe ground motions. The analysis indicated potential application prospect of FBRB in practical engineering.

A buckling-restrained brace (BRB) serves as a typical load-bearing and energy-dissipative device for the passive control of structures under seismic loading. A BRB is generally designed to not yield under frequently occurring earthquake (FOE) and wind loads, resulting in it having less effectiveness in vibration reduction compared with post-yielding performance. To address this dilemma, this study proposed the concept and technique details of the viscoelastic-yielding compounded BRB (VBRB). Different from a conventional BRB, a VBRB is fabricated by attaching the viscoelastic damper (VED) to the surface of a BRB’s steel casing, ensuring a compatible deformation pattern between the VED and the BRB’s steel core. A dynamic loading test of VBRB specimens was carried out in which 0.2 Hz~0.6 Hz in loading rate and a maximum of 550 kN in load-bearing capacity had been applied, verifying the feasibility and performance of the VBRB. Subsequently, a parametric design procedure was developed to determine the required VBRB parameters so that the maximum elastic drift response of the structure could be reduced to the code-prescriptive value. The wind-resistance and seismic performances of the VBRB were critically evaluated through dynamic time-history analyses on a 48-story mega VBRB-equipped frame designed according to the Chinese seismic design code (GB50011-2010), and the effectiveness of the approach was also verified. Results indicate that the VBRB has advantages over a conventional BRB by providing a multi-stage passive energy dissipation capacity, resulting in a better vibration-control effect than conventional BRBs for structures subjected to wind load and seismic excitations.

Steel shear panel dampers (SPDs) have been widely used for the seismic protection of structures. The seismic performance of SPD is limited by the buckling deformation and low cycle fatigue tearing of the web. This study proposes a new‐type buckling restrained shear panel damper (BRSPD), in which two octagon restrainers are utilized instead of rectangular ones. The novel BRSPD is developed to prevent its web plate from stress concentration and tearing at the early stage. A basic mechanism for the novel BRSPD was proposed. Quasi‐static tests were conducted to examine the behavior of the BRSPDs. The influence of the factors, such as the configurations of the restrainers and the gap size between the restrainer and the web plate, were investigated. The experimental results indicated that the proposed octagon restrainers can effectively restrain the out‐of‐plane deformation of the web plate. The BRSPDs with the proposed restrainers presented better energy dissipation performance than both the conventional SPD and those with rectangular restraining plates. The shape and the thickness of the restrainers had significant influence on the performance of the damper, while adding grease or rubber between the restrainer and web plate had little effect. The BRSPD with no gap between the plates had the highest equivalent viscous damping ratio.