Field-Dependent Stiffness of a Soft Structure Fabricated from Magnetic-Responsive Materials: Magnetorheological Elastomer and Fluid

Abstract

A very flexible structure with a tunable stiffness controlled by an external magnetic stimulus is presented. The proposed structure is fabricated using two magnetic-responsive materials, namely a magnetorheological elastomer (MRE) as a skin layer and a magnetorheological fluid (MRF) as a core to fill the void channels of the skin layer. After briefly describing the field-dependent material characteristics of the MRE and MRF, the fabrication procedures of the structure are provided in detail. The MRE skin layer is produced using a precise mold with rectangular void channels to hold the MRF. Two samples are produced, namely with and without MRF, to evaluate the stiffness change attributed to the MRF. A magnetic field is generated using two permanent magnets attached to a specialized jig in a universal tensile machine. The force-displacement relationship of the two samples are measured as a function of magnetic flux density. Stiffness change is analyzed at two different regions, namely a small and large deformation region. The sample with MRF exhibits much higher stiffness increases in the small deformation region than the sample without MRF. Furthermore, the stiffness of the sample with MRF also increases in the large deformation region, while the stiffness of the sample without MRF remains constant. The inherent and advantageous characteristics of the proposed structure are demonstrated through two conceptual applications, namely a haptic rollable keyboard and a smart braille watch.

Hybrid Magnetorheological Composites for Electric and Magnetic Field Sensors and Transducers

“…In particular, magnetorheological composites (MCs) have attracted an intense research interest, owing to their potential applications in a large number of multi-functional devices, including energy dissipation [ 10 ], vibration absorbing [ 11 ], muscle-like actuators [ 12 ], or sensors [ 13 , 14 , 15 ]. Recently, the application of MCs as sensors and transducers has become a hot research topic [ 16 , 17 , 18 , 19 ] due to their high socio-economic impact and the rapid development of various fabrication methods, including three-dimensional (3D) printing [ 20 , 21 , 22 ] or magnetorheological drawing lithography [ 23 ]. An excellent review in which some perspectives in the development of wearable polymer-based sensors are described has recently been published in Ref.…”

Stribeck Curve of Magnetorheological Fluid within Pin-on-Disc Configuration: An Experimental Investigation

“…The cohesion of chain formations causes an increase in the apparent viscosity of MR fluid [ 2 ]. This property is most often exploited by MR dampers [ 3 , 4 , 5 ], brakes/clutches [ 6 , 7 , 8 ], seals [ 9 , 10 ], or flexible structures [ 11 , 12 ]. The applicability of these MR devices in smart mechanical systems has several limitations.…”

Tunable Young’s Moduli of Soft Composites Fabricated from Magnetorheological Materials Containing Microsized Iron Particles

“…Thus, an ERF is generally utilized as a core layer of sandwich structures (beam, shell, and plate) to increase the damping property or alternate the modal characteristics, such as the natural frequency, of concentration of MRE layer. To compare the effect of each factor, five types of specimens were prepared, and the overall specimen production process was similar to the previous paper [25], but one of the MRF injection amount, the shape of the channel mold, the amount of curing agent entering the MRE layer, and the weight fraction of the CIP entering the MRE layer was varied and applied to each specimen. Prior to the experiment, a magnetic field generator was constructed in the universal tensile test machine.…”

“…Prior to the experiment, a magnetic field generator was constructed in the universal tensile test machine. Unlike the previous paper using a neodymium magnet [25], a magnetic circuit using solenoid coils was constructed so that a uniform magnetic field could be applied to the specimen. Fabricated specimens were fixed and tested in a tensile tester, and the directly measured force-displacement curves obtained from the universal tensile machine were converted to the stress-strain curves.…”

“…Recently, as a method of increasing the tunability of the Young’s moduli of MRE, a soft composite that used a different method from that of adding an additive to the MRE matrix was suggested. The suggested method introduced in [ 25 ] sought to fabricate soft composite consisted of two magnetic-responsive materials—an MRE as the skin layer and MRFs as the cores, which filled the void channels of the lower skin layer. The soft structure was investigated as the proof-of-concept by presenting one preliminary result which clearly shows the field-dependent stiffness.…”