Person: Huang, Jiangshui
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Huang
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Jiangshui
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Huang, Jiangshui
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Publication Highly deformable actuators made of dielectric elastomers clamped by rigid rings(AIP Publishing, 2014) Lu, Tongqing; Chiang Foo, Choon; Huang, Jiangshui; Zhu, Jian; Suo, ZhigangIn the nascent field of soft machines, soft materials are used to create devices that actuate robots, sense environment, monitor health, and harvest energy. The soft materials undergo large deformation in response to external stimuli, often leading to instability that is usually undesirable but sometimes useful. Here, we study a dielectric elastomer membrane sandwiched between two soft conductors, rolled into a hollow tube, pre-stretched in the hoop direction, and fixed at the ends of the tube to two rigid rings. This structure functions as an electromechanical transducer when the two rings are subject to a mechanical force and the two conductors are subject to an electrical voltage. We formulate a computational model by using a variational principle and calculate the large and inhomogeneous deformation by solving a nonlinear boundary-value problem. We demonstrate that large actuation strains are achievable when the height-to-radius ratio of the tube is small and the hoop pre-stretch is large. The model provides a tool to analyze various modes of instability and optimize the electromechanical performance.Publication Pattern formation in plastic liquid films on elastomers by ratcheting(Royal Society of Chemistry (RSC), 2016) Huang, Jiangshui; Yang, Jiawei; Jin, Lihua; Clarke, David; Suo, ZhigangPlastic liquids, also known as Bingham liquids, retain their shape when loads are small, but flow when loads exceed a threshold. We discovered that plastic liquid films coated on elastomers develop wavy patterns under cyclic loads. As the number of cycles increases, the wavelength of the patterns remains unchanged, but the amplitude of the patterns increases and then saturates. Because the patterns develop progressively under cyclic loads, we call this phenomenon as “patterning by ratcheting”. We observe the phenomenon in plastic liquids of several kinds, and studied the effects of thickness, the cyclic frequency of the stretch, and the range of the stretch. Finite element simulations show that the ratcheting phenomenon can occur in materials described by a commonly used model of elastic–plastic deformation.Publication Maximizing the Energy Density of Dielectric Elastomer Generators Using Equi-Biaxial Loading(Wiley-VCH Verlag Berlin, 2013-03-29) Huang, Jiangshui; Shian, Samuel; Suo, Zhigang; Clarke, DavidDielectric elastomer generators (DEGs) for harvesting electrical energy from mechanical work have been demonstrated but the energy densities achieved are still small compared with theoretical predictions. We show that significant improvements in energy density (560 J/kg with a power density of 280 W/kg and an efficiency of 27%) can be achieved using equi-biaxial stretching, a mechanical loading configuration that maximizes the capacitance changes. We demonstrate the capacitance of dielectric elastomers subjected to equi-biaxial stretches is proportional to the fourth power of the stretch. Quantification of the individual energy contributions indicates that attaining higher conversion efficiencies is limited by viscous losses within the acrylic elastomer, suggesting that still higher conversion efficiencies with other elastomers should be attainable with our novel mechanical loading design.Publication Dielectric elastomer actuators under equal-biaxial forces, uniaxial forces, and uniaxial constraint of stiff fibers(Royal Society of Chemistry, 2012) Lu, Tongqing; Huang, Jiangshui; Jordi, Christa; Kovacs, Gabor; Huang, Rui; Clarke, David; Suo, ZhigangA membrane of a dielectric elastomer deforms when a voltage is applied through its thickness. The achievable voltage-induced deformation is strongly affected by how mechanical loads are applied. Large voltage-induced deformation has been demonstrated for a membrane under equal-biaxial forces, but only small voltage-induced deformation has been observed for a membrane under a uniaxial force. This difference is interpreted here theoretically. The theory also predicts that, when the deformation of a membrane is constrained in one direction, a voltage applied through the thickness of the membrane can cause it to deform substantially in the other direction. Experiments are performed on membranes under equal-biaxial forces and uniaxial forces, as well as on fiber-constrained membranes of two types: a dielectric elastomer membrane with carbon fibers on both faces, and two dielectric elastomer membranes sandwiching nylon fibers. The experimental observations are compared with the theory.Publication The Thickness and Stretch Dependence of the Electrical Breakdown Strength of an Acrylic Dielectric Elastomer(American Institute of Physics, 2012) Huang, Jiangshui; Shian, Samuel; Diebold, Roger Mitchell; Suo, Zhigang; Clarke, DavidThe performance of dielectric elastomer actuators is limited by electrical breakdown. Attempts to measure this are confounded by the voltage-induced thinning of the elastomer. A test configuration is introduced that avoids this problem: A thin sheet of elastomer is stretched, crossed-wire electrodes are attached, and then embedded in a stiff polymer. The applied electric field at breakdown, \(E_{B}\), is found to depend on both the deformed thickness, h, and the stretch applied, \(\lambda\). For the acrylic elastomer investigated, the breakdown field scales as \(E_{B}\) = 51 h\(^{ − 0.25 }\) \(\lambda\)\(^{0.63}\). The test configuration allows multiple individual tests to be made on the same sheet of elastomer.Publication Large, Uni-directional Actuation in Dielectric Elastomers Achieved By Fiber Stiffening(American Institute of Physics, 2012) Huang, Jiangshui; Zhu, Jian; Clarke, David; Suo, ZhigangCylindrical actuators are made with dielectric elastomer sheets stiffened with fibers in the hoop direction. When a voltage is applied through the thickness of the sheets, large actuation strains are achievable in the axial direction, with or without pre-straining and mechanical loading. For example, actuation strains of 35.8% for a cylinder with a prestrain of 40%, and 28.6% for a cylinder without pre-strain have been achieved without any optimization. Furthermore, the actuation strain is independent of the aspect ratio of the cylinder, so that both large strains and large displacements are readily actuated by using long cylinders.Publication Spontaneous and Deterministic Three-Dimensional Curling of Pre-Strained Elastomeric Bi-Strips(Royal Society of Chemistry, 2012) Huang, Jiangshui; Liu, Jia; Kroll, Benedikt; Bertoldi, Katia; Clarke, DavidThree dimensional curls (“hemi-helices”) consisting of multiple, periodic and alternating helical sections of opposite chiralities, separated by perversions, are one of a variety of complex shapes that can be produced by a simple generic process consisting of pre-straining one elastomeric strip, joining it side-by-side to another and then releasing the bi-strip. The initial wavelength of the hemi-helix and the number of perversions are determined by the strip cross-section, the constitutive behavior of the elastomer and the value of the pre-strain. The hemi-helix has no net twist. Topologically, the perversions separate regions of the hemi-helix deforming principally by bending from those where twisting dominates.