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Flexible-die forming using a magnetorheological (MR) fluid can adjust the performance of flexible-die by changing the external magnetic fields in different regions, which shows great potential for improving process control flexibility in sheet metal forming. However, the existing research focuses on basic research of parts with simple structures, lacking in-depth research on the forming behavior of complex thin-walled components. In this paper, the configuration control of thin-walled stepped aluminum alloy parts by subregional magnetorheological flexible-die forming is conducted. The finite element analysis was used to predict the magnetic field distribution during the forming process under two different regional magnetic fields, that is, the central-dominated magnetic field and the fringing-dominated magnetic field. Then, the effect of subregional magnetorheological flexible-die control on the loading curve, part configuration, strain, and wall thickness distribution were analyzed. In addition, finite element simulations were applied to assist in studying the stress distribution of sheets during the deformation process under different loading conditions, as well as the stress loading paths of typical points. Results show that the adoption of the central-dominated magnetic field leads to a greater final deformation degree of the material at the third fillet and better attaching capability to the die at the third fillet. While under the fringing-dominated magnetic field, the deformation degree of the sheet is greater around the first fillet. From the perspective of stress and strain evolution in different regions, the influence mechanism of subregional magnetorheological flexible-die control on the configuration difference of stepped aluminum alloy parts is further clarified. This study can provide guidance for the process parameters control and further engineering application of this new technology in complex thin-walled components forming. [ABSTRACT FROM AUTHOR]

Grippers are commonly used as a technological tooling for manipulators. They enable robots to interact with objects in their work area. Grippers have a wide range of differentiation focused on the operation performed and the properties (e.g. shape) of the object being gripped. Their design and functionality are constantly being modified, tuned and developed by both academic and industrial units. Consequently, this paper presents a proposal for a lightweight jaw using MR fluid, which can be implemented in a jaw gripper (e.g. Robotiq 2F-140) to form a hybrid soft-rigid structure. In addition, methods are presented for studying the use of soft structures in a jaw gripper. As part of the work carried out, a model of the cushion and jaw of the gripper was developed, the FEM was used to obtain the character of the deformation when the object is axially plunged into it. Experimental plunging tests as well as dynamic tests of object transfer were also carried out. The work carried out allowed to demonstrate several key aspects of the grippers area. The soft structures of the grippers should be studied in terms of the force required to deform them. This determines their applicability to fragile and deformable objects. Dynamic measurements of the handling of objects of different shapes, with simultaneous measurement of force, allow the effectiveness of the use of soft structures in the gripper to be determined. Such experiments will make it possible to determine the measurable stability and repeatability of the grasp. The results of the research and experiments will be particularly applicable to robotic arms with relatively low lifting capacity. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) fluids can be utilized in one of the fundamental operating modes of which the gradient pinch mode has been the least explored. In this unique mode non-uniform magnetic field distributions are taken advantage of to develop a so-called Venturi-like contraction in MR fluids. By adequately directing magnetic flux the material can be made solidified in the regions near the flow channel wall, thus creating a passage in the middle of the channel for the fluid to pass through. This leads to unique variations of the slope in the pressure-flow rate characteristics. It can be stated that the effect of the MR fluid composition on the behaviour of the MR fluid in gradient pinch mode has not been thoroughly investigated yet. In this study, the behaviour of MR fluids was assessed with a dedicated pinch mode MR valve that provided a valuable insight into the contraction mechanism using fluorescence microscopy. Briefly, seven MR fluid samples were prepared with different particle concentrations (10%, 22% and 32 vol%) and mean particle sizes (2, 4.5 and 8.2 μm). It was found that the MR fluid sample with the larger particle size exhibits a significantly larger slope change observed in the pressure-flow rate characteristics. Increasing the particle size from 2 μm (base) to 8 μm resulted in the slope increase by a factor of 2.6 compared to the base sample. Increasing the particle concentration has a negligible effect on the pinch mode effect. Finally, these results were analysed using the modified Wuest equation, which is commonly used for characterizing sharp-edged orifices in low Reynolds number flow regimes. The simple equation was determined to describe the behaviour of MR fluids in gradient pinch mode with adequate accuracy. [ABSTRACT FROM AUTHOR]

Non-Newtonian behaviour of the Magnetorheological (MR) fluid under the influence of external magnetic field can be commissioned to design various applications such as MR brake, damper, and clutches, etc. Better design strategies, material selection and characterization led to realize the potential of MR brakes to replace conventional brakes. The present study emphasises on developing lightweight (1.8 kg) multi-rotor MR brake (MMRB). Finite element method magnetics (FEMM) software is utilized to determine the material required for a single-rotor MRB. FEMM material selection analysis is incorporated into the modeled MMRB, and the nature of magnetic flux density throughout the MR gap was obtained. Magnetic circuit analysis of the proposed brake is carried out to find torque estimation using analytical equations and Bingham plastic model. The proposed brake is fabricated and characterized using commercial MRF (132 DG, Lord Corporation). The study compares the torque outputs obtained experimentally with finite element analysis (FEA) and analytical approach. The average maximum magnetic flux density through FE analysis is found to be 0.45 T @ 3 A current. The average error between FE obtained and experimentally obtained torque output of the brake is around 5%. Further, an alternate design is proposed by utilizing same rotor diameter and number of electromagnetic coils. The new design is lighter in weight (0.8 kg) and exhibits enhancement in the torque output and torque to weight ratio by around 31% and 55%, respectively than the present design. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) fluids are utilized to develop a variety of electromechanical devices that have potential applications in the automotive, medical, aerospace, and other areas. Since yield stress is the most important design parameter of an MR fluid and its devices, it is dependent on the types of operational modes. This paper thoroughly examines the effects of the operational modes of MR fluids such as shear mode, and squeeze mode along with the impact of mixed-mode operation on the performance of MR fluids and devices. The study found that mixed-mode operation results in higher yield stress and offers better performance control for MR fluid devices compared to single-mode operation under the same working conditions. Several factors impact the performance of MR fluid devices in various operational modes discussed in the paper such as geometry, initial gap thickness, temperature, pressure, velocity, applied compressive strain, response time, magnetic particle composition, magnetic field, and other working factors. Therefore, there is a necessity to thoroughly examine the rheological and mechanical behaviors of MR fluids and the performance of MR devices in different operational modes and working circumstances, highlighting the experimental and theoretical findings conducted by researchers. [ABSTRACT FROM AUTHOR]

Purpose: With the advantages of simple structure, low energy consumption, and wide controllable damping range of magnetorheological (MR) damper, semi-active suspension with MR damper has become a promising application in the existing vehicle suspension system. However, the response time of MR fluid, the operation time of control system and the driving time of MR damper will result in response time delay together, which severe affect the vibration attenuating performance of the vehicle semi-active suspension system with MR damper. In this paper, a LQR controller incorporating NAGA-II algorithm considering response time delay (NSGA-II-TLQR) was developed to compensate for the response time delay of vehicle semi-active suspension system. Methods: Firstly, the mechanical property experiments of MR damper were carried out, and the direct model and the inverse model of MR damper were established by using genetic algorithm, respectively. Secondly, the model of a two-degree-of-freedom (2DOF) quarter vehicle semi-active suspension system with MR damper was built. Subsequently, the NSGA-II algorithm was introduced to optimize the weighting coefficient matrix of the LQR controller. Then the first-order Taylor series expansion was applied to the NSGA-II-LQR controller to predict the control force, which compensate for the response time delay. Finally, the performance was verified by simulation and experimental tests. Results: The results show that the body acceleration RMS values with NSGA-II-TLQR controller are decreased by 15.5% and 4.48%, the suspension deflection RMS values are decreased by 22.54% and − 1.22%, and the tire dynamic load RMS values are decreased by 10.32% and 5.38% compared with the passive suspension and the suspension with NSGA-II-LQR controller, respectively. Conclusions: The semi-active suspension with NSGA-II-TLQR controller has better performance in the ride comfort and handling stability. [ABSTRACT FROM AUTHOR]

In recent years, the application of non-uniform pressure in flexible-die forming, such as viscous pressure forming and magnetorheological pressure forming, has become increasingly prevalent in manufacturing thin-walled components. Non-uniform pressure is primarily employed to change the shape of the sheet, while its effects on thickness reduction and fracture behaviors remain intricate. In this study, the mechanisms of non-uniform pressure to decrease thickness reduction and delay fracture instability in bulge forming are revealed. Non-uniform pressure changes the principal stresses, resulting in distinct deformation behaviors. Numerical simulations indicate that both too large and too small pressure weights lead to severe thickness thinning and increase the risk of fracture instability. Theoretical equations of the polar strain and instability strain are derived to reveal the mechanisms. The characteristics of non-uniform pressure to decrease thickness reduction and delay instability are outlined. Viscous pressure bulge tests are conducted, and the experimental results of bulged shapes, thickness uniformity, polar strains, and instability behaviors validate the theories. The fracture strain under the non-uniform pressure condition shows a 5.6% increase compared with the uniform pressure condition. This study proves that non-uniform pressure can promote sheet formability, suggesting promising applications in sheet metal forming. [ABSTRACT FROM AUTHOR]

Sandwich structures are widespread in engineering applications because of their advantageous mechanical properties. Recently, their acoustic performance has also been improved to enable attenuation of low-frequency vibrations induced by noisy environments. Here, we propose a new design of sandwich plates (SPs) featuring a metamaterial core with an actively tunable low-frequency bandgap. The core contains magnetorheological elastomer (MRE) resonators which are arranged periodically and enable controlling wave attenuation by an external magnetic field. We analytically estimate the sound transmission loss (STL) of the plate using the space harmonic expansion method. The low frequency sound insulation performance is also analyzed by the equivalent dynamic density method, and the accuracy of the obtained results is verified by finite-element simulations. Our results demonstrate that the STL of the proposed plate is enhanced compared with a typical SP analog, and the induced bandgap can be effectively tuned to desired frequencies. This study further advances the field of actively controlled acoustic metamaterials, and paves the way to their practical applications. [ABSTRACT FROM AUTHOR]

The plastic deformation of the complex thin-walled components is not uniform. Applying a non-uniform load can decrease the thickness reduction and improve the thickness uniformity. In recent years, the application of non-uniform pressure to deform the sheet (such as magnetorheological pressure forming and viscous pressure forming) has attracted researchers' attention. However, the characteristics of the non-uniform pressure have not been researched. Control of the non-uniform pressure in the forming process lacks theoretical support. In this study, the mechanism of the non-uniform pressure in the viscous pressure bulge test is investigated. The pressure-carrying medium, called viscous medium, is semi-solid and flowable. The inhomogeneous flow behavior of the medium produces non-uniform pressure when the maximum is at the bulged pole. The inhomogeneous deformation behavior of the medium produces non-uniform pressure when the minimum is at the bulged pole. The effects of flow and deformation are opposite. The non-uniform pressure function is derived, and the evolution of the pressure is presented. During forming, the viscosity of the medium increases with the pressure, so the effect of the flow behavior increases, and the pressure weight at the pole increases. Viscous pressure bulge tests are carried out to verify the theory. The gradient and evolution of the pressure can be controlled by the loading velocity and the property of the medium. The results provide theoretical guidance for the control of the pressure in viscous pressure forming, and the methodology is expected to analyze the non-uniform pressure in other flexible die forming processes. [ABSTRACT FROM AUTHOR]

In order to reveal adsorption-regulation micromechanism and debonding micromechanism between wall surface and magnetorheological (MR) wall-climbing robot legs, an interparticle normal magnetic attraction (NMA) mechanics model was constructed based upon the magnetic-dipole theory. According to analysis of NMA mechanics, it was confirmed that the interparticle NMA could be intensified with enhancing magnetic-particle diameter but was weakened with ratio of adjacent magnetic-particles distance to magnetic-particle radius. It means that the adhesive capacity between MR wall-climbing robot legs and wall surface could be strengthened by increasing magnetic-particle size and decreasing interparticle distance. Furthermore, it was found that the NMA of the first particle in the magnetic chain was positively related to magnetic-particles number until the magnetic-particles number reached a critical value. Consequently, the adsorption ability between MR wall-climbing robot legs and wall surface could be effectively controlled by changing magnetic-particles number. Besides, the strongest NMA appeared at the middle of the magnetic chain. However, the weakest NMA locates at both ends of the magnetic chain. Thus, it could be concluded that the end of the magnetic chain would be separated from wall surface rather than fracture occurred in the middle of the magnetic chain when the MR wall-climbing robot legs divorced from wall surface. [ABSTRACT FROM AUTHOR]

Recently, numerous studies have demonstrated that the physics-informed neural network (PINN) can effectively and accurately resolve hyperelastic finite deformation problems. In this paper, a PINN framework for tackling hyperelastic-magnetic coupling problems is proposed. Since the solution space consists of two-phase domains, two separate networks are constructed to independently predict the solution for each phase region. In addition, a conscious point allocation strategy is incorporated to enhance the prediction precision of the PINN in regions characterized by sharp gradients. With the developed framework, the magnetic fields and deformation fields of magnetorheological elastomers (MREs) are solved under the control of hyperelastic-magnetic coupling equations. Illustrative examples are provided and contrasted with the reference results to validate the predictive accuracy of the proposed framework. Moreover, the advantages of the proposed framework in solving hyperelastic-magnetic coupling problems are validated, particularly in handling small data sets, as well as its ability in swiftly and precisely forecasting magnetostrictive motion. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive investigation into a 3D simulation of magnetorheological (MR) conical bearings, focusing on considering viscous dissipation using the conjugated heat transfer approach. The behavior of MR fluids is expressed through the utilization of the Bingham-Papanastasiou constitutive equation. Notably, this study considers variations in viscosity and yield stress as functions of both magnetic field intensity and temperature. The study utilizes a multidisciplinary approach, encompassing fluid dynamics, magnetism, and heat transfer, to model and analyze the behavior of MR fluids within conical bearing geometries. The governing equations containing Cauchy momentum, energy, and Maxwell equations are solved using the finite element method. This research delves into the impacts of viscous dissipation on the functional and characteristic attributes of conical bearings. The energy equations in solid and fluid domains and extended considerations to the plug region within viscous dissipation are specifically addressed. Extensive validation is performed through a comparative analysis involving experimental, numerical, and analytical studies to ensure the validity of results. The results reveal the substantial impact of temperature on both the characteristics and functionality of magnetorheological conical bearings. [ABSTRACT FROM AUTHOR]

The vibrations generated in the two-wheeled vehicles like motorcycles due to road irregularities such as cracks, potholes, and bumps on the road cause discomfort for the rider as well as the pillion. These vibrations are reported to cause lower back pains, musculoskeletal effects, fatigue, and long-term health issues. Particularly, electric two-wheelers are more susceptible to these vibrations caused by the road and need attention. This paper presents an innovative technique for the reduction of vibrations at prominent locations in the electric two-wheeler to improve the rider's comfort. All measured accelerations are about vertical direction (along z-axis as per ISO 2631-1 standard). Passive and Semi-active damping treatments namely, Room temperature vulcanizing Silicone rubber and Magnetorheological elastomer (MRE) were applied on the test vehicle at strategic locations of vibration. Both were compared for their effectiveness in reducing the vibrations. Results showed that MRE based damping technique proved better vibration isolation at the strategic locations. The weighted root mean square acceleration as well as vibration dose values were found to decrease with the help of damping treatments thus improving the rider's overall comfort level. [ABSTRACT FROM AUTHOR]

The diverse applications of magnetorheological elastomer (MRE) drive efforts to understand consistent performance and resistance to failure. Stress relaxation can lead to molecular chain deterioration, degradation in stiffness and rheological properties, and ultimately affect the life cycle of MRE. However, quantifying the energy and molecular dynamics during stress relaxation is challenging due to the difficulty of obtaining atomic-level insights experimentally. This study employs molecular dynamics (MD) simulation to elucidate the stress relaxation in MRE during constant strain. Magnetorheological elastomer models incorporating silicone rubber filled with varying magnetic iron particles (50–80 wt%) were constructed. Experimental results from an oscillatory shear rheometer showed the linear viscoelastic region of MRE to be within 0.001–0.01% strain. The simulation results indicated that stress relaxation has occurred, with stored energies decreased by 8.63–52.7% in all MRE models. Monitoring changes in energy components, the highest final stored energy (12,045 kJ) of the MRE model with 80 wt% Fe particles was primarily attributed to stronger intramolecular and intermolecular interactions, revealed by higher potential energy (3262 kJ) and van der Waals energy (− 2717.29 kJ). Stress relaxation also altered the molecular dynamics of this MRE model as evidenced by a decrease in kinetic energy (9362 kJ) and mean square displacement value (20,318 Å2). The MD simulation provides a promising quantitative tool for elucidating stress relaxation, preventing material failure and offering insights for the design of MRE in the nanotechnology industry. [ABSTRACT FROM AUTHOR]

Magnetorheological polishing technology is widely used in the processing of high-precision optical elements. One of the determining factors in the magnetorheological polishing technology is the nature and quality of a nanoabrasive present in a magnetorheological suspension. In this study, a method has been developed for the sol–gel synthesis of amorphous silica nanospheres used as a nanoabrasive for magnetorheological polishing of water-soluble crystals used to manufacture nonlinear optical elements for laser technology. The practical success has been achieved by incorporating the synthesized silica nanoabrasive into a magnetorheological suspension. The physicochemical characteristics of the resulting nanoabrasive have been presented. Electron microscopy data have confirmed the spherical morphology of SiO2 particles, and it has been found that the particle size distribution varies in a range of 40–60 nm, thus ensuring the uniformity and high quality of treating the surfaces of optical elements with the magnetorheological suspension. The structure-related properties of the SiO2 nanoabrasive have been studied by X-ray powder diffraction. The incorporation of the SiO2 nanoabrasive into the magnetorheological suspension has made it possible to achieve the high-quality processing and cleanliness of the surface, as well as to ensure the finishing polishing of the surface of KDP single crystals to roughness values of no more than 6 Å. The results of the work are of interest for optimizing the process and improving the technology of magnetorheological polishing. [ABSTRACT FROM AUTHOR]

In order to improve the problem of poor sedimentation and easy leakage when applied to MR devices of magnetorheological (MR) fluid, this work made a magnetorheological grease (MRG) material with 70 % carbonyl iron powder and used Anton Paar rheometer to test its flow curve under different currents. The Bingham model is selected and the Origin software is used for fitting calculation. In addition, due to the advantages of rheological properties of MRG, the double rod MRG damper applied to the vibration reduction system was designed. The calculation of the main component parameters and the dimensions of the magnetic field Road size were conducted during the design process. After the physical completion of the MRG damper, its mechanical performance was tested, and the results showed that the maximum damping force reached 1.1 kN when the current was 1.8 A. Subsequently, the Bouc Wen model and Dahl model were introduced to describe the nonlinear behavior of the magnetorheological grease damper. The prediction accuracy of the two models was compared using a coefficient of determination, and it was found that the Bouc Wen model can more accurately and efficiently simulate the dynamic characteristics of the magnetorheological grease damper, with a coefficient of determination value above 0.99. Finally, the relationship between model parameters and current was established through least squares fitting, and most of the parameters were fitted with a cubic polynomial relationship with current. [ABSTRACT FROM AUTHOR]

Based on the traditional steel spring floating slab track, a quasi-zero-stiffness magnetorheological damping (MRD) track system is constructed by introducing the horizontal spring negative stiffness mechanism and MRD. First, the mechanical model of the system is established, the static analysis is done, and the effects of each parameter on the nonlinear behaviors of the system are numerically analyzed. Then, the dynamics equation of system is set up; subsequently, the amplitude–frequency response equation is obtained by means of the average method. The influences of different parameters on the dynamic response of the system are analyzed. Finally, three semi-active control methods, PID control, fuzzy-PID control and frequency + fuzzy-PID control, are designed, and then, the vibration reduction effect of each control method is simulated. The results present that the proposed system has good vibration isolation effect in low frequency region and a high bearing capacity. The larger nonlinear coefficient, vertical damping ratio, horizontal damping ratio, Coulomb damping force, viscous damping ratio and input current are beneficial to improve the low frequency vibration of the system. By adopting the frequency + fuzzy-PID control method, the peak of force transmissibility and the initial vibration isolation frequency are reduced by 61.9 and 14.2%, respectively, compared with that of the uncontrolled system. The proposed system presents good vibration isolation performance outside the frequency range of 1–3 Hz. [ABSTRACT FROM AUTHOR]

The physical and chemical characteristics of hydrophobic protection of cement rock and concrete surfaces, using the binders based on polyurethane, elemental sulfur, and nanodimensional fillers of Tarkosil and thermally modified peat, are discussed. It is shown that a combined use of the physical texture-formation methods and an optimal selection of the protective coating chemical composition results in a significant increase of the wetting angle and the solid phase surface energy. It is found out that a directional orientation of the magnetically sensitive particles in the magnetorheological composites in a magnetic field is among the most effective methods for improving the protective coating properties. [ABSTRACT FROM AUTHOR]

Magnetic (B) fields are an intriguing route for manipulating soft materials. While most research on B field manipulation of diamagnetic polymers has focused on alignment of ordered structures or anisotropic domains, our recent work uncovered a previously unrecognized effect: B fields alter hydration and hydrogen bonding in thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) solutions. Despite the well-known thermoreversible coil-to-globule transition and hydrogel formation upon heating, the impact of magnetic fields on these structural and rheological transitions has been largely unexplored. In this study, we thoroughly examined the temperature-dependent magnetorheology of PNIPAM solutions, varying B field strength, polymer content, and molecular weight. Linear magnetorheology reveals that increasing the B field intensity decreases the dynamic moduli of the resulting physical hydrogel, across polymer concentrations (5–20% wt) and molecular weights (30–108 kDa), by up to an order of magnitude. Conversely, the gelation onset temperature does not change substantially. This weakening effect is more pronounced at longer magnetization times and slower temperature ramp rates. Nonlinear magnetorheology following hydrogel formation reveals a two-step yielding process characteristic of attractive-driven glasses, suggesting that magnetization decreases both the stress and length scales associated with mesoglobule cage breaking. We propose that B fields impact the hydrogel rheology by altering the mesoglobule size and water content. This work uncovers essential understanding of how B fields alter hydrogel formation in PNIPAM solutions, broadening the scope of magnetic field manipulation of diamagnetic polymer solutions. [ABSTRACT FROM AUTHOR]

Scissor-like isolation platform (SIP) with magnetorheological damper (MRD) has been commonly studied and applied successfully in vehicle vibration isolation. This paper concerns passive nonlinear magnetorheological (MR) characteristics of the SIP via geometric nonlinearity induced by MRD's layout ways. A dynamic parametric model of the SIP with six assembly types is derived based on Lagrange equation. Then, the parameter analysis is performed to estimate MR damping function in SIP. The analytical steady-state response of the isolator is derived using harmonic balance method, and its effectiveness is validated with numerical results. Metrics are defined to access the performance of the isolator, followed by comparison on displacement transmissibility for six types. The effect of MR damping coefficient and input amplitude on the performance of the isolator is investigated. Finally, comparative study with existing isolators is conducted. Results indicate that, passive MR damping is dependent on vibration displacement, which is beneficial to suppressing peak transmissibility with a little effect at non-resonant frequencies. The results also reveal that the isolator by type 1 or 3 has broader isolation band over other types. And the SIP in type 1 has wider isolation band and lower peak transmissibility compared with existing isolators in allowable workspace. [ABSTRACT FROM AUTHOR]

Non-visual auditory camouflage plays a major role in the art of underwater deception. In this work, a hybrid active/semi-active omnidirectional cloaking shell structure composed of alternate complementary piezoelectric and smart viscoelastic (PZT/SVE) actuator layers is proposed that can effectively conceal a three dimensional underwater macroscopic object from broadband incident sound waves. The smart hybrid structure incorporates a finite sequence of fully active parallel-connected multimorph PZT constraining layers inter-stacked with semi-active SVE core layers both of which are collaboratively operative in the framework of a Particle Swarm Optimized (PSO) multiple-input multiple-output active damping control (MIMO-ADC) scheme. The elasto-acoustic modeling of the problem is conducted by coupling the spatial state space methodology based on the classical three-dimensional exact piezoelasticity theory with the wave equations for the inner and outer acoustic domains. The acoustic cloaking performance of proposed configuration is evaluated for four distinct classes of highly functional SVE interlayer materials with tunable (field-dependent) rheological properties, namely, magnetorheological elastomer (MRE), shape memory polymer (SMP), electrorheological fluid (ERF), and magnetorheological shear thickening polishing fluid (MRSTPF). Extensive numerical results reveal significant broadband reductions of the far-field backscattering amplitude in the ( f ∞ θ = π , k ex R ex ) as well as the percentage error of external cloaked field (% Err) by incorporating a sufficient number of smart multimorph PZT/SVE material layers. Furthermore, it is concluded that comparable low frequency acoustic cloaking effects is possible without expenditure of any external energy just by employing the entirely inactive MRSTPF-based cloak as an alternative to the semiactive or fully active multimorph PZT/SVE cloaks. The outcome of proposed study can advantageously serve as the first step towards practical development and experimental implementation of future high performance smart acoustic cloaking devices with expanded broadband near-perfect omnidirectional invisibility for three dimensional objects of diverse geometries. [ABSTRACT FROM AUTHOR]

Cobalt particles are often used as fillers in magnetorheological elastomer (MRE) due to their potential advantages. This study aimed to assess the physical, morphological, magnetic, and optical properties of cobalt-based MRE (Co-MRE). To achieve this, several isotropic samples with different concentrations of cobalt and polydimethylsiloxane (PDMS) were created. Finite Element Method Magnetics (FEMM) 2D simulation software and a Vibrating Sample Magnetometer (VSM) were used to assess the magnetic properties. Morphological properties were observed with a Field Emission Scanning Electron Microscope (FESEM) and physical properties were examined using X-Ray Diffraction (XRD). Ultraviolet–Visible (UV–Vis) and Photoluminescence (PL) spectroscopy were used to study the optical properties. FEMM 2D showed that 7 wt% of Co-MRE had the highest magnetic flux density. VSM indicated that 7 wt% of Co-MRE had the strongest magnetic saturation. Morphological properties revealed that 7 wt% of Co-MRE had a rougher surface than 0–5 wt%. XRD showed that 7 wt% of Co-MRE had more cobalt elements. UV–Vis indicated that 5 wt% of Co-MRE had a precise result with some noise. PL spectroscopy showed that 7 wt% of Co-MRE had a higher emission peak and a broader shape at 475–525 nm excitation wavelength, while 0 wt% had a broader shape graph at 550–600 nm. While these properties are beneficial, it is important to balance the sensitivity and elasticity of MRE for stable applications in assistive sensor devices. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomers (MREs) are known to be smart composite materials able to storing and dissipating part of the energy when subjected to external excitation (magnetic field, temperature, frequency). In this paper, anisotropic magnetorheological elastomers containing 20, 30, and 40% of the micrometric iron particles MRE prepared. The magnetorheological characteristics such as, storage modulus, loss modulus and loss factor MRE measured by dynamic mechanical analysis (DMA) over a range of frequencies (0.01 to 100 Hz), strain amplitudes (0.01 to 20%) and temperatures (0 to 100°C). The magnetorheological elastomer during dynamic mechanical characterization is subjected to a constant magnetic field intensity value of 0.2 T. Increasing the excitation frequency also increases the magnetomechanical properties of the MRE. The temperature has a reversible effect with the frequency, we see that when we increase the temperature, the magnetomechanical properties of the MRE decrease. The experimental results precisely showed the variation of the dynamic moduli (storage modulus, loss modulus and shear loss factor) of the anisotropic MRE loaded with 20, 30, and 40% ferromagnetic particles as a function of the parameters of influence such as: frequency and temperature. [ABSTRACT FROM AUTHOR]

Background: One of the biggest challenges in soft robotics is the variability and controllability of stiffness. Jamming-based approaches have been of interest to change stiffness dramatically by increasing friction between grains, layers, or fibers. Besides, magnetorheological elastomers (MREs) that exhibit magnetic field-dependent viscoelasticity have significant potential as a stiffness variation material. This study investigates the unique mechanics of magnetic jamming of MRE sheets exploring stiffness change both due to jamming and variable viscosity. Methods: Sample MREs and flexible neodymium-iron-boron (NdFeB) magnets are manufactured. Uniaxial tensile tests supported with digital image correlation are performed to characterize the materials. Multi-layer jamming structures comprised of MREs and NdFeB magnets are developed and validated through 3-point bending experiments and finite element simulations. Results: Results show that the stiffness of the multi-layer structure is higher under magnetic field. Furthermore, the stiffness change is increased when MREs are used instead of PDMS as layers. Conclusion: This study proves the concept of magnetic jamming of MRE layers. The results are crucial for the possible soft robotic implementation of the proposed hybrid stiffening approach combining jamming with viscoelasticity modification. [ABSTRACT FROM AUTHOR]

Purpose: Semi-active control is considered to be very interesting for its engineering sophistication/effectiveness like the active control strategy, however, requiring significantly lesser amount of control effort/input. In view of the devastating damages of soft-storey building structures in case of real-life seismic events, a study on semi-active vibration control for vulnerable structures like soft-storey buildings appears very interesting. Methods: The magnetorheological (MR) damper is taken as the control device which produces control force through modulating its damping coefficient with the help of external input voltages in a semi-active control framework based on the widely used Linear Quadratic Gaussian (LQG) control. The Bouc–Wen hysteresis model is considered to calculate the control force. A realistic five-storey building with soft-storey at the ground is considered for validation. Besides, the performance of LQG control is compared with the proportional-integral-derivative (PID) control. Results: It is observed that LQG-based semi-active control strategy has been able to perform satisfactorily (in reducing soft-storey response) with the cost of surprisingly insignificant amount of control effort (with supply voltage in the range, 0–2.5 V) by reducing the peak response as 67.5%, 78.05%, 67.57%, 75%, and 51.02% against El Centro, Northridge, Kobe, Bhuj, and Tohoku earthquakes, respectively, while 68.85%, 79.42%, 65.26%, 73.38%, and 51.65% in case of root-mean-square response. Higher range of supply voltage is found to provide even better control performance. Conclusion: In view of the satisfactory control performance, the semi-active control with MR dampers using LQG control is well encouraging in protecting the highly vulnerable soft-storey building structures under seismic events. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to advance the field of marine propulsion dynamics by investigating coupled torsional and transverse vibrations in shaft systems and proposing a novel approach for their mitigation. The focus is on incorporating Magnetorheological (MR) dampers controlled by an Adaptive Neuro-Fuzzy Inference System (ANFIS) to enhance adaptability and responsiveness. Methods: A sophisticated numerical model, based on a modified Jeffcott rotor model, is introduced to forecast the intricate dynamics of the shaft system. A meticulously formulated mathematical model for the MR damper is presented and validated through experimental investigations. The MR damper is subjected to sinusoidal displacement inputs at varying current levels, and the resulting force–displacement profiles are analyzed. The proposed numerical model for the shaft system is validated through experimental analysis, and the integration of MR dampers controlled by ANFIS is investigated. Investigations are conducted at different rotational speeds (rpm) to evaluate vibration reduction and stability. Results: The semi-active control system, comprising MR dampers and the ANFIS controller, has demonstrated superior performance compared to passive strategies. The reduction in torsional vibrations by a percentage reduction index of 21.01% and transverse vibrations by 28.36% underscores the potential of this innovative approach in dynamically controlling marine propulsion systems. The ANFIS controller's ability to dynamically adjust damping force has proven crucial in ensuring optimal performance. Conclusion: This study highlights the potential of MR dampers controlled by ANFIS in enhancing dynamic control for marine propulsion systems. Findings contribute valuable insights into addressing vibration-related challenges, emphasizing potential resilience and optimization in the maritime industry. The presented semi-active control system demonstrates superior performance, paving the way for innovative approaches in marine engineering. [ABSTRACT FROM AUTHOR]

The paper presents an experimental study and numerical simulation of stress relaxation behavior of isotropic and anisotropic magnetorheological elastomers (MREs) made from silicone rubber filled with micro-sized carbonyl iron powder. Effects of applied constant strains and magnetic fields of an electromagnet on the stress relaxation of the MREs were investigated for 10 h using the single relaxation test with double-lap shear samples. The isotropic MRE showed a linearly elastic behavior, while the anisotropic MRE indicated a highly nonlinear elastic response. The shear stress and relaxation modulus of anisotropic MRE are much higher than those of isotropic MRE. The shear stress of the MREs increased with increasing the constant strain, while their relaxation modulus decreased. The shear stress and relaxation modulus of the MREs within the first 0.25 h boosted with raising the magnetic flux density to about 0.5 T. However, the shear stress and relaxation modulus of the MREs under strong magnetic fields declined considerably after 0.25 h testing. This reduction was attributed to the temperature rise in the MRE samples caused by the heating of the electromagnet. The stress relaxation behavior of the MREs was examined using a four-parameter fractional derivative model. The model parameters were obtained by fitting the relaxation modulus to the measured data of the MREs. The shear stress and relaxation modulus with long-term predictions estimated from the studied model were in good agreement with the measured data for the MREs at various applied strains and under low magnetic fields. The model-predicted values did not agree well with the experimental data of the MREs under high magnetic fields because of the sample temperature gain caused by heat generation of the electromagnet. Therefore, the investigated model can be used to predict the long-term relaxation stress of the MREs under high magnetic fields of permanent magnets. [ABSTRACT FROM AUTHOR]

Due to its excellent filling capacity, good forming accuracy, and low die manufacturing costs, the sheet/tube flexible-die forming process has become an important supplement to traditional rigid die forming processes, widely used in the multi-variety, small and medium-sized batch manufacturing of complex thin-walled components in high-end manufacturing fields, such as aviation, aerospace, and automobiles. To match the deformation characteristics of different types of sheet/tube components, flexible mediums with different physical and mechanical properties were used as pressure-carrying dies and exhibited their respective advantages. Among them, what is remarkable is that magnetorheological materials, a type of intelligent material, have been introduced into flexible-die forming and develop into sheet/tube magnetorheological controllable flexible-die forming process. Real-time control of magnetorheological flexible-die performance can be achieved through an external adjustable magnetic field, improving the process control flexibility of the forming process and enhancing the forming performance and quality of parts. This article reviews the latest research progress in the sheet/tube magnetorheological controllable flexible-die forming process in recent years, and elaborates on the forming principles, control patterns, forming methods, and forming mechanisms. Finally, the future development direction of the magnetorheological controllable flexible-die pressure forming process for sheet/tube materials is prospected. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomers (MRE) are smart materials that have recently attracted considerable interest. The mechanical properties of MREs change significantly in the presence of a magnetic field. This study investigates the MRE properties and proposes a new model for designing systems using MRE. First, an MRE material fabrication process is introduced, and the dynamic properties of the MRE are investigated under different magnetic field strengths, frequencies, and amplitudes. The smooth Coulomb friction model is well known, representing the amplitude-dependent mechanical properties well. However, the model was inefficient when describing materials' properties at the low strain frequency (< 2 Hz). In this study, an improved Coulomb friction model has been developed to improve this problem by adding the strain velocity influence factor. Furthermore, the fractional viscous and variable stiffness models represent the material properties dependent on the frequency and magnetic field. Finally, a simple procedure, with easy computation, is proposed for determining the model parameters. The model results are compared with two classical models, the Coulomb model and the Bouc-Wen model. The developed model overcomes the disadvantages of the smooth Coulomb friction model when applied at low frequencies. Simulation and experimental results show that the proposed model achieves a deviation of just under 6 % in most cases, lower than when implementing the classical Coulomb friction (8 %) and hysteresis Bouc-wen models (7 %). The model also achieved similar accuracy when used for laminated MRE. [ABSTRACT FROM AUTHOR]

To investigate the effect of graphite additive specific gravity on the rheological properties of magnetorheological grease (MRG), graphite magnetorheological grease (GMRG) with 70% mass fraction of carbonyl iron powder and 0%, 2%, 5%, 8%, and 10% mass fractions of graphite powders were prepared using grease as the matrix. An Anton Paar rheometer was used to measure the rheological characteristics of five materials in oscillatory and steady-state shear modes. The results reveal that the incorporation of graphite powder into MRG yields superior yield stresses. In addition, the graphite additive could enhance the viscoelastic characteristics of the MRG and had little effect on the linear viscoelastic interval of the material. Frequency scanning experiments of temperature changes indicate that GMRG is a temperature-hardened material, and that the temperature stability of GMRG viscosity at different frequencies is better, but GMRG exhibits more elasticity than viscosity. However, it is significant to highlight that the presence of graphite reduces the relative magnetorheological action of the MRG. [ABSTRACT FROM AUTHOR]

Background: Magnetorheological (MR) fluid has recently been used in a variety of applications, including vibration control, prostheses, and tactile devices. A magnetic field is used to control the rheological properties of the MR fluid (MRF), allowing for a high pressure drop, high shear stress, and reversibility of these features. The modifiability imparts smartness to the material, and recent studies have investigated their behavior extensively. Purpose: The present work involves the design of an MR fluid-based actuator to function as an ankle in a prosthetic foot. Methods: The initial design constraint of the MR valve and stroke length of the MR damper have been identified based on anthropometric constraints and biomechanical requirements of below-knee amputees (BKA). Second, magnetostatic analysis has been performed to solve an approximated parametric magnetic model (PMM) based on linear electromagnetic systems. Finally, finite element magnetostatic (FEMS) analysis was conducted to understand the magnetic flux density (MFD) of the MR fluid and the pressure drop was modeled and obtained using the Bingham model. Next, optimization of the damper was done. For this, the optimization goal functions were to (a) maximize damping force and (b) minimize the mass of the damper valve (by minimizing the volume of the damper and MR fluid), hence minimizing the weight of the prosthetic ankle. The geometric dimensions of the MR valve are optimized using an integration of a multi-objective genetic algorithm (MOGA) in MATLAB and FEMS in ANSYS APDL software. MOGA chooses values for design variables that are constrained within the specified bounds, and they are coupled by the FEMS analysis; this routine is automated and repeated for all possible values within the specified bounds. Results: It was observed that the results of MFD computed from PMM are valid for low ranges of current; however, it over-estimates MFD beyond 0.5 A. Furthermore, optimal solutions obtained are plotted on a Pareto front, which satisfies the objective function of maximizing the damping force and minimizing the weight of the damper. The optimization findings show trade-offs between damping force and damper mass. Conclusions: The optimized outcomes show enhancements in the cost function as compared to the unoptimized values. The proposed methodology integrating FEMS and MOGA shows promise and can be extended to other applications of MR dampers as well. [ABSTRACT FROM AUTHOR]

The shear yield stress is an important parameter for the industrial application of magnetorheological (MR) fluids. A test equipment was designed and built to perform investigations on the behaviours of compression and shear after squeeze of MR fluids. Mathematical expression of magnetic flux density was further established. Furthermore, the magnetic field distribution of the test device based on two-coil mode and single-coil mode was simulated and compared using finite element analysis(ANSYS/Multiphysics). An experimental test system was fabricated and modified based on the final conditions and simulation results. The compression and shear after squeeze performances of MR fluids were tested. The results showed that a smaller initial gap distance or a larger compressive strain corresponds to a larger compressive stress under the same external magnetic field strength. The shear yield stress after the squeeze of MR fluids increases quickly with the increasing compression stress and the increasing magnetic flux density. This test equipment was thought to be suitable for studying the compression and shear after squeeze performances of MR fluids. [ABSTRACT FROM AUTHOR]

Nano-fabrication techniques have demonstrated their vital importance in technological innovation. However, low-throughput, high-cost and intrinsic resolution limits pose significant restrictions, it is, therefore, paramount to continue improving existing methods as well as developing new techniques to overcome these challenges. This is particularly applicable within the area of biomedical research, which focuses on sensing, increasingly at the point-of-care, as a way to improve patient outcomes. Within this context, this review focuses on the latest advances in the main emerging patterning methods including the two-photon, stereo, electrohydrodynamic, near-field electrospinning-assisted, magneto, magnetorheological drawing, nanoimprint, capillary force, nanosphere, edge, nano transfer printing and block copolymer lithographic technologies for micro- and nanofabrication. Emerging methods enabling structural and chemical nano fabrication are categorised along with prospective chemical and physical patterning techniques. Established lithographic techniques are briefly outlined and the novel lithographic technologies are compared to these, summarising the specific advantages and shortfalls alongside the current lateral resolution limits and the amenability to mass production, evaluated in terms of process scalability and cost. Particular attention is drawn to the potential breakthrough application areas, predominantly within biomedical studies, laying the platform for the tangible paths towards the adoption of alternative developing lithographic technologies or their combination with the established patterning techniques, which depends on the needs of the end-user including, for instance, tolerance of inherent limits, fidelity and reproducibility. [ABSTRACT FROM AUTHOR]

Viscoelastic properties of magnetoactive elastomers with spherical and plate-shaped filler have been studied. Four series of samples based on silicone elastomer and carbonyl iron microparticles have been prepared. A series of samples with a concentration of magnetic filler from 30 to 60 wt % which differed in the shape of filler particles (spherical and platelike) and in their distribution in the polymer matrix (isotropic and anisotropic). The magnetorheological properties of the obtained magnetoactive elastomers have been examined by dynamic mechanical analysis. Storage modulus values for samples of different compositions are in the range of 10–100 kPa. It has been shown that anisotropic materials are stiffer than the isotropic counterparts and demonstrate a higher magnetorheological effect: the increase in the elastic modulus of an anisotropic sample with the maximum filler content exceeds an order of magnitude in a magnetic field of 1 T. At the same filler concentrations, materials based on platelike iron are stiffer than those based on spherical iron. At low magnetic filler concentrations, the use of platelike iron makes it possible to achieve a higher magnetic response of the material; at high filler concentrations, the increase in the elastic modulus is greater for samples based on spherical particles. The anisotropic materials exhibit a more pronounced Payne effect. [ABSTRACT FROM AUTHOR]

Purpose: For the drop-induced shock mitigation system with magnetorheological energy absorbers (MREAs), the time lag of MREA has a nonnegligible influence on the shock mitigation performance. This paper proposed a minimum transmitted load control method considering time lag (MTL-T) is proposed. Methods: First, the influence of a time lag on the shock mitigation performance is analyzed, and the relationship between the theoretical controllable force and the actual controllable force of the MREA with a time lag is given. Then, taking the controllable force of traditional MTL control method as the theoretical value and the "soft-landing" as the control target, the control algorithm of MTL-T control method is derived. Finally, the simulation is conducted for the shock mitigation system with variable parameters controlled by MTL-T, and the comparative performance of MTL-T control method and other methods is given. Results: The theoretical analysis shows that MTL-T control method can make the shock mitigation system with a time lag achieve the control target of "soft-landing". The advantages of MTL-T control method are shown by the comparative performance of the MTL-T control method and other methods. Conclusions: Once the parameters of the system and the impact intensity are obtained, the MTL-T can be determined. The adaptability of MTL-T control method is verified. Compared with other control method, the MTL-T has a small peak transmitted load while making full use of MREA. [ABSTRACT FROM AUTHOR]

A planetary-type cluster magnetorheological polishing device with a rotating magnetic field was proposed to solve the problems of abrasive accumulation and low polishing efficiency caused by the untimely restoration of the conventional magnetic chain. Considering the microstructural deformation and squeeze-strengthening effect of magnetorheological polishing fluid, a material removal rate model was established based on the principle of fluid dynamic pressure and verified by experiments. The relationships between material removal rate or roughness and processing parameters were confirmed by multiple linear regression analyses, respectively. And the processing parameters optimization was made by linear weighting method under the premise of establishing the evaluation system. The results show that the eccentricity and angular velocity ratio are proportional and inversely proportional to MRR, respectively. When the polishing fluid is squeezed, the material removal rate can be significantly increased from 7 to 21 nm/min, but the roughness will be reversed at a gap of less than 0.9 mm. After the optimization of processing parameters, the workpiece roughness after rough and fine polishing was reduced from 1.079 μm and 1.083 μm to 0.346 μm and 0.184 μm, with a reduction of 67.9% and 83.01%. [ABSTRACT FROM AUTHOR]

Current source is an indispensable component of magnetorheological (MR) systems. Though MR fluid has a phase change as fast as in 1 ms, the response of MR damper (MRD) to generate the damping force may be two orders of magnitude longer. Therefore, the rapid response of current source is a key to realize the real-time semi-active control of MR devices. This study proposes a programmable high-speed, low-cost current source exclusively for MR devices based on the synergy between supercapacitor and Buck converter (i.e., SSBC current source). SSBC current source features a strategy consisting of a lifting phase of supercapacitor and a following maintaining phase of Buck converter. Specifically, the high power density of supercapacitor contributes to rapidly lifting/raising the initial current, and then, like a "relay race", the expected output is maintained through a Buck converter. Theoretical modeling and experiments are performed systematically. The response times (@ 95% of expected outputs) measured are 0.44, 0.84 and 1.88 ms for the outputs of 3, 6 and 9 A, respectively; these values are highlighted as the fastest level in this field. Besides, the response can be up to 24.6 and 43.7 times faster than the cases using supercapacitor and Buck converter to directly drive the MRD, respectively. SSBC current source is employed to generate a sequence of currents/magnetic inductions, only four variables of which need to be controlled programmatically: the order of lifting and maintaining phases, switching time of lifting phase, PWM duty cycle of Buck converter and duration of maintaining phase. The response time stability is verified by 100 cycles of on/off tests, showing a fluctuation of only 1.1%, which indicates a very reliable high-speed response. This study provides an exclusive power supply with a novel strategy for MR devices, which is believed to be an important promotion for MR technologies. [ABSTRACT FROM AUTHOR]

Magnetorheological shear thickening polishing (MRSTP) was experimentally demonstrated to achieve nano-level surface quality in previous studies. The aim of work is to further investigate numerical simulation and material removal characteristics during the MRSTP process. The apparatus of magnetic field generation was designed and developed. The model of magnetic field distribution was imported to computational fluid dynamics (CFD) module to generate desired polishing environment. Polishing stress behaviors were analyzed based on various polishing parameters through the CFD simulation results. It was found that the pressure on the workpiece surface decreased with the increase of the rotational speed of the workpiece while it increased with the increase of the flow velocity of the MRSTP media. A continuous increment in shear stress on the workpiece surface was observed with the increase of the rotation speed of the workpiece and the flow velocity of the MRSTP media. Based on the characteristics of polishing pressure, material removal rate (MRR) model of MRSTP process was established. A serial of MRSTP experiments were conducted on aluminum 6061. Surface roughness (Sa) of 79.0 nm was obtained, which was improved over 77%. The simulated model and MRR model were experimentally validated. The average error between theoretical and experimental results was 4.1%. It can provide a useful guidance for the novel MRSTP process. [ABSTRACT FROM AUTHOR]

The ultra-smooth planarization processing of single crystal sapphire is the basis for the realization of high-performance optoelectronic/micro-electronic devices, and its extremely high hardness and stability bring great challenges to the high-efficiency and high-quality planarization. A cluster magnetorheological global dynamic pressure polishing method was proposed by combining the collective constrained polishing disk of a 3-D microstructure with the reciprocating variable gap between tool and workpiece. Four types of magnetorheological polishing methods were used for comparative experimental study, and a single-factor experiment was conducted on process parameters such as the hole diameter and hole gap in the collective constrained polishing disk and variable gap frequency and amplitude of the workpiece. The results show that the flow field characteristics and the structure degree of the carbonyl iron powders in the processing area can be controlled by the collective constrained polishing disk and the reciprocating variable gap motion of the workpiece. The polishing force of the polishing pad on the workpiece surface is increased. Meanwhile, the extrusion scratch removal of abrasive particles and the stretching reflow update can be realized. Compared with traditional magnetorheological polishing, the material removal rate is increased by 154.6%, and the surface roughness is reduced by 67.1%. The average surface roughness of single crystal sapphire decreases from Ra 5.61 to Ra 0.33 nm within an area of 120 μm × 96 μm after 5-h polishing using the optimized process. The global dynamic pressure formed by the collective constrained polishing disk and the reciprocating variable gap of the workpiece can control the force exerted by the polishing pad on the workpiece surface and improve the polishing efficiency and surface quality. [ABSTRACT FROM AUTHOR]

A magnetorheological (MR) damper is effective and economical for miscellaneous applications in automotive, mechanical, civil, and relative fields. A parameter tuning methodology independent of manual trial-and-error has received much technical interest for controlling vibrations. The present work contributes mathematical and Simulink modeling followed by MR damper design and development for vibration optimization of the single degree of freedom system. A Simulink model of an MR damper is performed on the mathematical model for vibration control, and the MR damper's tuning parameters are experimentally investigated to control the resonance frequency. Theoretical simulated results and its experimental verification show that increasing current raises the force to control the resonance frequency in an MR damper. The present approach provides a concise and improved platform for dynamic vibration absorber in the current potential market and the highly interested control community for the development of the distinctive attributes of the MR Damper. [ABSTRACT FROM AUTHOR]

An investigation has been made into the rotational motion of particles of a disperse system caused by hydrodynamic and magnetic forces and into its macroscopic manifestations. A method has been proposed for the rotation of such a system in a stationary field for determining the main components of the dynamics and kinematics of transformation of particles' rotation into their translational movement, i.e., the transfer of the angular momentum between individual particles and the disperse system on the whole. Factors have been established for an optimal impact on a disperse system by a magnetic field and its rotation effects on the achievement of a goal: nondestructive control over the system's structure or its modification. [ABSTRACT FROM AUTHOR]

Conductive polypyrrole nanotubes were synthesized with a two-step one-pot synthesis. During synthesis, the nanotubes were decorated with magnetite nanoparticles at different concentrations granting them magnetic properties. The characterization of the tubes revealed differences from the theoretical reactions. A bidisperse magnetorheological fluid (MRF) was prepared by mixing the composite polypyrrole nanotubes/magnetite nanoparticles with commercial carbonyl iron spherical microparticles in silicone oil. The rheological properties of the bidisperse system were studied under the presence of magnetic field at room and elevated temperature. An enhancement of the MR effect with the presence of the nanotubes was observed when compared with a standard MRF consisted only of magnetic microparticles. Due to the faster magnetic saturation of the nanotubes, this enhancement is exceptionally high at low magnetic fields. The stability of the system is studied under dynamic conditions where it is revealed that the nanotubes keep the standard particles well dispersed with the sedimentation improving by more than 50%. [ABSTRACT FROM AUTHOR]

Recent developments in minimally invasive medicine have been fomenting the development of smaller and controllable devices. However, one of the major challenges toward decreasing invasiveness of medical procedures is miniaturizing actuators to milli- or microscale while maintaining reliability. This is the context in which magnetic actuation surfaces as an excellent candidate for designing such devices. Among the gaps in currently minimally invasive medicine is the lack of active locomotion capabilities in wireless devices. Worm-like motion has been successfully demonstrated with magnetorheological robots before; however, an in-depth analysis of how these beam-shaped robots interact with the supporting surface has not been conducted yet. In this work we analyze several support configurations between soft bodied robot over a flat surface and propose an algorithm with the goal of predicting the behavior of a given magnetic robot under an applied magnetic field. Robots ranging from approximately 10–40 mm were manufactured and used for the verification of our proposed model and algorithm. Comparison between simulation and experiment results showed good agreement indicating that this methodology can be a critical tool during the design stage of magnetic soft robots. [ABSTRACT FROM AUTHOR]

A magnetorheological electro-Fenton composite polishing technology was proposed that enables chemical and mechanical "double enhancement" of the machining process to improve processing efficiency. In this process, a novel high-efficiency catalytic oxidation magnetorheological chemical polishing slurry is configured. Frictional wear experiments are carried out in a magnetorheological electro-Fenton environment to study the corrosion mechanism and material removal behavior of electro-Fenton chemical reactions during magnetorheological electro-Fenton compound polishing. Finally, cluster magnetorheological electro-Fenton compound polishing tests are carried out using the optimized parameters. The results show that the •OH generated by the reaction in the friction and wear of the magnetorheological electro-Fenton composite can effectively oxidize GaN in the friction and wear trajectory to produce a loose cracked Ga2O3 corrosion layer. The corrosion effect increases and then decreases as the current increases from 20 to 60 mA; the corrosion effect also shows a trend of increasing and then decreasing when the rate of H2O2 supplementation increases from 0.30 to 0.60 g/min. The best corrosion effect was achieved when the current was 20 mA, and the H2O2 was replenished at a rate of 0.30 g/min, with a mass fraction of 58.6% of the element O on the sample surface. Using silica sol to polish the GaN for 1 h under the same process, magnetorheological electro-Fenton compound polishing can reduce the surface roughness from Ra 2 to 0.8 nm, while ordinary magnetorheological polishing roughness is only reduced to Ra 1.86 nm. A magnetorheological basis combined with electrochemical means to control and enhance the chemical effect can significantly improve the polishing efficiency. [ABSTRACT FROM AUTHOR]

Phononic crystals (PCs) consist of a periodic arrangement of inclusions in a matrix material, and have garnered a great deal of interest owing to a phenomenon known as band gap frequencies in which particular frequency ranges are not able to propagate through the PCs. The aim of this work is to study the effects of magneto-elastic coupling and other parameters such as randomness in geometrical properties, volume fraction and size of inclusions on longitudinal wave propagation and, in particular, on the appearance of stop-band frequencies. The results indicate that the most important parameters deciding whether a frequency is in a stop-band or a pass-band are the randomness in geometrical properties and piezomagnetic coupling. It was observed that piezomagnetic coupling can lead to a widening of the first stop-band range for a periodic microstructure. Moreover, while randomness in particle size leads to a stop-band range and reduced wave transmission in the second pass region, randomness in particle position leads to removal of the pass band ranges compared to periodic structures. Additionally, the influence of piezomagnetic coupling becomes insignificant in fully random structures. [ABSTRACT FROM AUTHOR]

The free vibration properties of a sandwich beam with axially graded facings and a magnetorheological fluid core are studied. The facings and core are modeled using the Euler–Bernoulli and Timoshenko beam theories, respectively. The problem is discretized using the Rayleigh–Ritz method. The approached complex eigenmodes method is implemented for solving the resulting nonlinear eigenvalue problem numerically. The effects of multiple parameters, i.e., facings' material distribution, functionally graded material's gradient index, boundary conditions, constraining and core layers' thickness, and magnetic field effect on the free vibration properties, are thoroughly studied. The obtained results reveal these parameters' significant impact on the frequency and loss factor of the system. [ABSTRACT FROM AUTHOR]

In this study, conductive polyindole (PIn) was coated onto initially fabricated magnetic iron oxide (Fe3O4) particles via chemical oxidative polymerization, and the synthesized core–shell structured hybrid smart particles were used as smart electrorheological/magnetorheological (EMR) materials. The synthesized Fe3O4/PIn particles were characterized using scanning electron microscopy and transmission electron microscopy. In addition, the chemical composition of the synthesized particles was confirmed using Fourier-transform infrared spectroscopy. Their magnetic properties were further analyzed using VSM. Consequently, the Fe3O4/PIn particle-based suspension, which was both magnetic and conductive, was found to exhibit interesting dual stimuli under both external electric and magnetic fields. Various rheological measurements, including shear simple steady shear and dynamic tests, were employed to evaluate the behavior of typical EMR suspensions. Furthermore, the dielectric properties of the particles were analyzed using an LCR meter. Based on the dielectric spectrum data, the relaxation time (λ) was estimated to be 1.5 × 10–8 s at the maximum frequency (λ = 1/2πfmax). Measurements conducted using a Turbiscan indicated enhanced sedimentation stability of the particles owing to a decrease in the particle density from 4.34 to 2.93 g/cm3. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the mechanical and rheological properties of magnetorheological elastomer (MRE) in marine ecosystems. The prepared samples comprised silicone rubber (SR) and 70 wt% micron-sized carbonyl iron particles (CIPs), immersed in an artificial marine ecosystem using salt water (Natrium Chloride) for 30 days. The mechanical properties of MRE samples were evaluated using hardness and quasi-static tensile tests. While the rheometer was used to investigate the rheological properties of their storage modulus condition with magnetic field stimulation. Further analysis of the defects and damages caused by salt water ageing was done through morphological observation using scanning electron microscope (SEM) technology. The results showed that the hardness and tensile strength of MRE samples that were soaked in salt water were affected over time. Lower values of hardness and tensile strength were obtained after 30 days due to the presence of Na+ and Cl−, which acted as an accelerator to the hydrolyzation process of the MRE. The process then, enhanced the water ingress capability into the matrix to cause the molecular changes. Interestingly, for rheological properties, 30 days of salt water ageing allowed the water molecules to move the MRE matrix molecular chains apart, a process known as plasticization and thus increasing the MR effect. Furthermore, morphological evidence was established to determine the MRE changes during salt water ageing. The research findings should greatly contribute to a better understanding of the effect of salt water on the performance of MRE. [ABSTRACT FROM AUTHOR]

The phenomenon of discontinuous shear thickening (DST) is observed in suspensions of solid particles with a very high-volume fraction. For suspensions of ferromagnetic particles, this transition can also be triggered by the application of a magnetic field as discussed by Bossis et al. (2016). Here, we explore the rheological behavior of a bidisperse suspension made of magnetic-carbonyl iron (CI) and non-magnetic-calcium carbonate (CC) particles with a brush-like coating of the same superplasticizer molecule. We highlight the synergetic effect of non-magnetic particles whose inclusion in the percolated frictional network amplifies the effect of the magnetic field on the remaining fraction of magnetic particles. In plate-plate geometry, a small fraction of ferromagnetic particles (about 5%) is sufficient to trigger the transition by the application of a magnetic field and optimum for the increase of viscosity. The progressive interpenetration of the coating layers of polymer and the demagnetizing field can explain this behavior. [ABSTRACT FROM AUTHOR]

Electrochemical magnetorheological finishing (EC–MRF) is an ultrasmooth planarization method that etches a workpiece surface with a controllable electrochemical (EC) method and then removes the etching layer synergistically through a variable-stiffness magnetorheological (MR) flexible polishing pad. The polishing efficiency is greatly improved. Moreover, a damage-free flat surface is obtained. In this paper, single-crystal gallium nitride (GaN) is used as a research object. The electrolyte solution and etching electric potential difference are first optimized through electrochemical etching experiments, and then single-crystal GaN wafers are processed by EC–MRF. The results demonstrate that the NaOH electrolyte solution has the best etching effects among KMnO4, Na2S2O8, and NaOH electrolyte solutions under an etching electric potential difference of 60 V. By adjusting the etching electric potential difference, the etching rate and degree of the surface are controlled. Under an etching electric potential difference of 20 V in the NaOH electrolyte solution, the material removal rate (MRR) in EC–MRF reaches 867.2 nm/h, which is 113% higher than that of conventional MRF; the surface roughness decreases from Ra 6.5 to Ra 0.9 nm. The synergy between chemical etching and mechanically flexible removal are achieved by adjusting the electrochemical electric potential difference and machining clearance in MRF while processing. A damage-free polished surface of GaN wafers with surface qualities of Ra 0.6 nm are obtained after processing by EC–MRF for 3 h. [ABSTRACT FROM AUTHOR]