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Current and Outlook on Manufacturing and Processing Technologies
Published in Yoseph Bar-Cohen, Advances in Manufacturing and Processing of Materials and Structures, 2018
In addition, the tentacles can be made to have controlled rigidity using electrorheological fluid (ERF). Such fluids have the property of increasing the viscosity in the presence of an electric field, and this effect has been known for more than 60 years (Winslow, 1949). Generally, ERF materials are made from suspensions of an insulating base fluid and particles having size of about 0.01 to 0.1 μm and volume fraction between 20% and 60% (Block and Kelly, 1988). The rigidization effect is thought to arise from the difference in the dielectric constants of the fluid and particles. In the presence of an electric field, the particles, due to an induced dipole moment, form chains along the field lines. In milliseconds, the ERF changes its consistency from a liquid to a viscoelastic gel.
Vibration damping by structural friction in drive systems with multiple-disc clutches
Published in Zbigniew Osiński, Damping of Vibrations, 2018
Variable viscosity can be achieved in some mixtures of oils and powders, but the best properties are exhibited by silicon oils with a polymer powder suspended in it [51, 62]. An electrorheological fluid can behave not only as a dissipating medium but also as an energy accumulator which is of great significance in a vibrating system. More detailed information about the fluids and their applications can be found in [28, 51, 62, 65]. We can learn that the suspended matter consists of particles with a diameter of 1 up to 100 μm. Immersed in mineral or silicon oils it produces a fluid with a density close to that of water. The electrorheological fluid called FL-fluid can be used within a wide range of temperatures, namely from −40°C up to 200°C. The fluid FL-Versa, based on linseed oil and lime water operates within the range of −10°C up to 90°C but it is not as expensive as FL-Fluid. The extent of solidification of the FL-fluid depends on the electric field, which affects viscosity and shear forces developed in the fluid (see Fig. 8.41). Growth of the current density leads to a growth of the electric field intensity (see Fig. 8.42).
Constitutive relations
Published in Roderic S. Lakes, Viscoelastic Solids, 2017
“Smart” materials are those which can respond in an active way to mechanical loads. A smart material may contain embedded sensors which provide information concerning the strain, temperature, or degree of damage in the material [2.11.6]. Sensor information can inform the user that an overload condition is present or that repair is necessary. To achieve a true smart response, the sensor data are input to a control system, which may contain a microprocessor that controls actuators within the material to reduce the deformation or repair the damage. Sensors and the actuators are discussed in the context of experimental methods in §6.3. For example, piezoelectric materials generate an electrical signal when strained and also deform in response to electrical excitation. Piezoelectric materials have been used both as sensors and as actuators. Another class of actuator material is electrorheological fluids, which have a viscosity that can be controlled by an electric field [2.11.7]. They are fluid-solid composites. A representative electrorheological fluid contains particles of corn starch dispersed in silicone oil.
Liquid-crystalline behaviour and electrorheological effect of phthalocyanine-based ionic liquid crystals
Published in Liquid Crystals, 2021
Aikebaier Reheman, Shuangying Hu, Lianjun Cao, Danhua Xie, Guiyang Yan, Jiwei Wang
The electrorheological fluid (ERF) has been extensively investigated as a kind of smart materials showing stimuli-responsive character because of its wide potential applications in various smart devices including actuators, dampers, clutches, robotics, and drug delivery etc [1–4]. When they are applied under an external electric field, ERFs change rapidly and reversibly in viscosity and fluidity, and achieve an adjustable transformation from liquid-like to solid-like phase. Suspensions of conducting and polarisable particles blending in insulating liquids are typical ERFs, and they can form a chain-like particulate structure along the direction of the external electric field strength, which results in electrorheological (ER) effect. Lots of particular materials have been used as ER particles, including high dielectric inorganics such as silica [5], titanium dioxide [6], titanate [7], and grapheme oxide [8] as well as organic conducting polymers such as polyaniline [9], polypyrrole [10], polyindole [11], polyphenlenediamine [12] and poly(p-phenylene) [13]. For these kinds of ERFs, the polarisation property including dielectric constant difference between the particles and the base liquids, and optimal conductivity play an important role on the ER effect. Recently, phthalocyanine (Pc) and related macrocyclic compound have attracted considerable attention due to their excellent electronic and polarisable properties [14–16], and Pc-based materials have also been investigated for ERFs [17–19].