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Integral abutment bridges (IABs) have become popular with departments of transportation throughout the United States due to their lower maintenance and construction costs and longer servic...

Magnetorheological (MR) fluid, whose rheological properties can be changed reversibly by applied magnetic field, offers superior capabilities and opportunities since its invention. The most crucial feature of MR fluid is its controllable and continuous yield stress. Taking this advantage, MR fluid is gaining popularity in various medical applications to meet their force/torque requirements. In this review article, progress of medical applications of MR fluid in the last two decades are systematically reviewed, mainly focused on six categories: lower limb prosthesis, exoskeleton, orthosis, rehabilitation device, haptic master, and tactile display. With MR fluid, natural and stable limb motions in lower limb prostheses, exoskeletons, and orthoses, flexible muscle trainings in rehabilitation devices, and high transparency and resolution haptic feedback can be realized. Relevant discussions and future perspectives are also provided.

At present, for the widely used Duffing-type bi-stable energy harvesters (D-BEH) with smooth nonlinear forces, there is a trade-off between large equilibrium point coordinates and small potential energy differences. In this study, programmable nonlinear force technologies are used to customize a piecewise bi-stable nonlinear force. Then, a novel piecewise bi-stable energy harvester (P-BEH) is designed to solve this trade-off. The results show that when the coordinate of the equilibrium point is 10 mm, the potential difference of the P-BEH is only 0.05 mJ, while that of the D-BEH is as high as 0.37 mJ. Therefore, the P-BEH can easily overcome the potential difference to make inter-well vibration at the excitation level of 2 m/s2, while the D-BEH can only perform intra-well vibration. Compared with the D-BEH, the P-BEH results in a 46% increase in the peak power and a 767% increase in the bandwidth. Simulation and experiment show that the proposed P-BEH has small potential differences and large equilibrium point coordinates, making it have better energy harvesting performance than the D-BEH.

Making full use of the magnetically controllable rheological properties of magnetorheological (MR) fluid, MR actuators have been applied in many engineering fields. To adapt to different application scenarios, parameters of MR actuators often need to be optimized. Previous MR actuator optimization was focused on finding optimal combinations of geometric dimensions and physical parameters that meet certain requirements. The parts with optimized dimensions were still in regular shape, which might not bring optimal damping performance. Therefore, in this paper, shape optimization of MR damper piston based on parametric curve is performed for the first time. First, the regional magnetic saturation problem in the previous prototype is stated. Then, the MR damper with normal piston is simulated as a reference. Later, Bezier curve, one of the typical parametric curves, is used to form the piston with optimized parameters, and the MR damper with optimized piston is also simulated. Finally, prototypes of the MR dampers with normal and optimized pistons are fabricated and tested. Compared with the MR damper with normal piston, the one with optimized piston has larger field dependent force and total damping force under relatively large current, with about 52% and 24% maximum increasing percentage, respectively. The controllable force range of the MR damper with optimized piston is also larger than that with normal piston.

Nonlinear forces have been widely introduced into vibration energy harvesting to improve its performance. Generally, sources of nonlinearity include magnet forces, spring forces, geometric and material nonlinearity, etc. However, these nonlinear forces cannot be manipulated arbitrarily. It is very promising if the nonlinear forces can be customized according to requirements, in which the performance of the energy harvester can be further optimized. Therefore, the purpose of this study is to develop a kind of vibration energy harvester (VEH) that can customize the nonlinear forces. The nonlinear force customization device consists of a pre-compressed spring, a miniature bearing, and a raceway, which are designed according to the nonlinear forces. As an example, the device is installed at the end of a piezoelectric cantilever beam, and mono-stable, bi-stable and tri-stable energy harvesters are customized, respectively. Simulation and experiments prove its effectiveness. The nonlinear force customization device enables designers to obtain the desirable nonlinear forces for the vibration energy harvesters.

Nonlinear forces obtained via springs, magnets, buckling beams, etc., have been widely introduced into vibration energy harvesting, vibration isolation and nonlinear energy sink to improve performance. Although obtaining customized nonlinear forces as desired is difficult, it is quite useful to improve the dynamic performance. Therefore, a device capable of customizing nonlinear forces is developed in this study. The device consists of a pre-compressed spring, a bearing and a raceway, which are designed according to the nonlinear forces to be customized. It is assumed that the nonlinear forces to be customized are continuous (not necessarily smooth). As examples, a hardening nonlinear system, a softening nonlinear system, a bistable system, a tri-stable system, and a piecewise nonlinear system are customized in this study. Simulations and experiments prove its feasibility. The device enables designers to obtain the most suitable nonlinear forces for the dynamic systems. It can be easily applied to energy harvesting, vibration isolation, and nonlinear energy sink, etc.

Due to low power consumption and fast response, magnetorheological (MR) dampers are widely used in various engineering applications. To enhance the performances, efforts have been made to increase the field dependent force with the same power consumption. However, the fluid viscous force is also increased significantly, which is undesirable in practical use. To tackle this problem, the focus of this paper is to design, simulate, and test an MR damper with multi-grooves (small multiple annular flow gaps) on piston for performance enhancement. First, the detailed design of the proposed MR damper is provided. Then, a coupled field model to describe the characteristics of MR fluid in different regions of MR damper is derived. Based on this model, multiphysics simulations are performed using COMSOL Multiphysics. Parametric analysis of the number and width of multi-grooves is also conducted. Experimental results of the two MR dampers without and with multi-grooves are given and compared with the simulation results. The advantages of MR damper with multi-grooves over the one without multi-grooves and the accuracy of the coupled field model are validated by experiments and simulations. This is the first time that the advantages of MR damper with multi-grooves are validated by experiments. Compared with MR damper without multi-grooves, MR damper with multi-grooves has larger damping force and controllable force range, as well as less increment of fluid viscous force while keeping the same increase of field dependent force. The performance of MR damper with multi-grooves could be further improved by increasing the number and decreasing the width of multi-grooves.

The control of the longitudinal pulsating force and the vibration generated is very important to improve the stealth performance of a submarine. Magnetorheological elastomer (MRE) is a kind of intelligent composite material, whose mechanical properties can be continuously, rapidly and reversibly controlled by an external magnetic field. It can be used as variable-stiffness components in the design of a semi-active dynamic vibration absorber (SDVA), which is one of the effective means of longitudinal vibration control. In this paper, an SDVA is designed based on the MRE's magnetic-induced variable stiffness characteristic. Firstly, a mechanical model of the propulsion shaft system with the SDVA is proposed, theoretically discussed and numerically validated. Then, the mechanical performance of the MRE under different magnetic fields is tested. In addition, the magnetic circuit and the overall structure of the SDVA are designed. Furthermore, electromagnetic and thermodynamic simulations are carried out to guarantee the structural design. The frequency shift property of the SDVA is found through dynamic simulations and validated by a frequency shift experiment. Lastly, the vibration absorption capacity of the SDVA is investigated. The results show that the magnetorheological effect of the MRE and the frequency shift of the SDVA are obvious; the SDVA has relatively acceptable vibration absorption capacity.