Investigation of the well-dispersed magnetorheological oil-based suspension with superparamagnetic nanoparticles using modified split Hopkinson pressure bar

Magnetorheological (MR) fluids are classified as smart materials whose viscoplastic characteristics change under the magnetic field. They are widely applied for dynamic energy dissipation due to their rapid thickening under the external magnetic field. In this work, the core–shell suspension of superparamagnetic iron oxide-based nanoparticles was synthesized and dispersed in silicone oil. Much effort has been made to prepare suspension meeting requirements of MR fluid. The experimental squeezing flow response was studied using a modified split Hopkinson pressure bar (SHPB) with various shear rates. Tests with modified SHPB show that MR fluid rapidly responds to the compression thickening and forming chain-like structures. MR fluid dissipates the energy generated during compression stress tests. This study presents a simple and cost-effective synthesis way suitable for MR fluid formation for its dynamic energy dissipation application.

Investigation of Thermoplastic Polyurethane Finger Cushion with Magnetorheological Fluid for Soft-Rigid Gripper

This paper presents a study of penetrating a pin into a magnetorheological fluid (MR) cushion focused on the force measurement. The research is supported by detailed finite element analysis (FEA) of the magnetic field distributions in several magnetic field exciters applied to control rheological properties of the MR inside the cushion. The cushion is a part of the finger pad of the jaw soft-rigid gripper and was made of thermoplastic polyurethane (TPU) using 3D printing technology. For the pin-penetrating setup, the use of a holding electromagnet and a magnetic holder were considered and verified by simulation as well as experiment. In further simulation studies, two design solutions using permanent magnets as the source of the magnetic field in the cushion volume to control MR fluid viscosity were considered. The primary aim of the study was to analyze the potential of using an MR fluid in a cushion pad and to investigate the potential for changing its viscosity using different magnetic field sources. The analysis included magnetic field simulations and tests of pin penetration in the cushion as an imitation of object grasping. Thus, an innovative application of 3D printing and TPU to work with MR fluid is proposed.

Layer-by-Layer Repair of Small-Scale Damage of Fused Silica Based on the Magnetorheological Method

The magnetorheological (MR) repair method can effectively repair the small-scale damage of fused silica optics and further improve the laser-induced damage threshold of fused silica optics. However, at present, the rules of MR repair of small-scale damage of fused silica are not clear and cannot provide further guidance for the repair process. In this paper, the fused silica damage samples were repaired layer by layer by the MR method. The number and size changes of all the surface damage, the morphology, the fluorescence area distribution, and photothermal-absorption value of a single typical small-scale damage were measured. Through dark field scattering imaging, it is found that when the repair depth is 5 μm, the repair completion rate of damage with a transverse size less than 50 μm can reach 44%, and the repair efficiency decreases gradually with the repair process. Focusing on the whole repair process of a single typical, small-scale damage—due to the flexible shear removal mechanism of the MR method—the repair process of damage can be divided into three stages, which as a whole is a top-down, from outside to inside process. The first stage is the process of removing the surface of the damage layer by layer. In this process, MR fluid will introduce pollution to the inside of the damage. In the second stage, MR fluid begins to repair the inside of the damage. In the third stage, the MR ribbon completely covers the inside of the damage, and the repair effect is the most obvious. The measurement results of photothermal absorption and fluorescence area distribution of damage confirm this process. The photothermal absorption value and fluorescence area distribution of damage do not simply decrease with the repair process. On the contrary, they gradually increase first, and then decrease significantly when the damage depth reaches less than 1 μm. As the thickness of the MR ribbon is 1 μm, the reduction in the photothermal absorption value and fluorescence area of the damage is due to the process of repairing the inside of the damage. The results show that the absorbent impurities inside the small-scale damage of fused silica are the main factor affecting the performance. The key to repairing the small-scale damage of fused silica by the MR method is that the damaged interior must be repaired effectively. This paper outlines the MR repair method of small-scale damage of fused silica, which is of great significance to optimize the MR repair process.

Haptic Interface with Twin-Driven MR Fluid Actuator for Teleoperation Endoscopic Surgery System

Magnetorheological fluids (MRFs) are composite materials made of ferromagnetic particles, medium oils, and several types of additives. We have developed an actuation system for the fine haptic control of leader-follower robots. In this study, we developed a haptic interface with two link-type twin-driven MR fluid actuators and two MR fluid brakes for a teleoperation endoscopic surgery system and conducted evaluation tests for a remote operational task with a leader-follower robot system. For evaluations, we adopted the NASA-TLX questionnaire as a subjective assessment method. According to the experimental results, the total success rates were 0.462, 0.333, and 0.591, for the first haptic, middle no-haptic, and second haptic phases, respectively. The force information of the haptic forceps helped users to perceive grasping sensation on their fingers. Statistical analyses on the answers to the questionnaire indicate no significant differences. However, a decreasing tendency in the mental stress in the complicated manipulation tasks for fragile objects is observed.

Orthosis with a controllable plantar height for fall prevention using a compact magnetorheological fluid brake

In this study, a compact magnetorheological (MR) fluid brake embedded in an orthosis was designed and fabricated to maintain plantar height for use in lateral fall prevention, and its performance and the fall prevention effect of the orthosis were evaluated. The results of the brake design and fabrication indicated that the MR fluid brake has the advantage of being compact, lightweight, and power-saving at 88.4 mm long, 128 g, using two AA batteries. Performance tests of the brake indicated that it was able to generate sufficient force (125 N) to maintain plantar height. Furthermore, through the assessments of lateral fall, the center of gravity and center of pressure inclination angle of a subject wearing the orthosis without the MR brake was determined to be 4.0°, as opposed to 4.4° with the MR fluid brake in the ON state. Therefore, the moment of force acting on the subject to prevent fall was larger, making them more stable when the MR fluid brake was in the ON state.

Tunable Stiffness and Damping Study on Flexible PVC Cantilever Structure Embedded with MR Fluid

The stiffness and damping of a flexible smart cantilever structure controlled by a magnetic field is investigated in this research. The cantilever structure is fabricated by using flexible polyvinyl chloride as a host structure of rectangular cross-section embedded with magnetorheological (MR) fluid. The deflection of the cantilever structure at the free end is used to analyze the stiffness change of the cantilever structure. The stiffness of the specimen with MR fluid at magnetic flux density of 0.171T is greater than that of the specimen without subjected to magnetic field. The strength of the applied magnetic field is directly related to the structure’s stiffness. Under the influence of a magnetic field, the MR fluid embedded inside the flexible PVC cantilever structure significantly dampens the vibrations of the structure.

Design and testing of a conventional clutch filled with magnetorheological fluid activated by a flexible permanent magnet at low compressive load: Numerical simulation and experimental study

In this research article, the working of conventional clutch (CC) filled with magnetorheological (MR) fluid was tested at low compressive load. The flexible permanent magnetic sheet (FMS) controlled the chain strength of MR fluid. A single clutch plate based on FMS was fabricated and tested on the developed test rig. The characteristics of the developed single plate MR clutch (SPMRC) were found by the testing and mathematical calculations. Magnetic circuit analysis presents the magnetic field distribution in the developed MR clutch. The mathematical expression for the torque transmission due to shear and compression is presented. COMSOL Multiphysics 5.3a software is used for the magnetic field simulation at different loading conditions. The temperature distribution in the developed clutch is simulated and experimented. It is observed from the results that the input shaft oscillation in the reduces more during disengagement in the SPMRC than the CC.