Enhanced anisotropic response of dielectric elastomer actuators with microcombed and etched carbon nanotube sheet electrodes

Fang, Xiaomeng; Li, Ang; Yıldız, Özkan; Shao, Huiqi; Bradford, Philip D.; Ghosh, Tushar K.

doi:10.1016/j.carbon.2017.05.067

Cited by 23 publications

(14 citation statements)

References 35 publications

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“…From equations (3) and ( 4), we know that the natural curvature can be correlated to a change in the stretch of one layer relative to another. Recent work on electrically active polymers has utilized the anisotropic actuation of dielectric elastomers of carbon nanotube electrodes to generate uniaxial stretch in the direction of fiber orientation [37,38], so we will examine the response of these bistable shells to the uniaxial stretch along the directrix of one layer.…”

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confidence: 99%

Snapping of bistable, prestressed cylindrical shells

Jiang¹,

Pezzulla²,

Shao³

et al. 2018

EPL

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Bistable shells can reversibly change between two stable configurations with very little energetic input. Understanding what governs the shape and snap-through criteria of these structures is crucial for designing devices that utilize instability for functionality. Bistable cylindrical shells fabricated by stretching and bonding multiple layers of elastic plates will contain residual stress that will impact the shell's shape and the magnitude of stimulus necessary to induce snapping. Using the framework of non-Euclidean shell theory, we first predict the mean curvature of a nearly cylindrical shell formed by arbitrarily prestretching one layer of a bilayer plate with respect to another. Then, beginning with a residually stressed cylinder, we determine the amount of the stimuli needed to trigger the snapping between two configurations through a combination of numerical simulations and theory. We demonstrate the role of prestress on the snap-through criteria, and highlight the important role that the Gaussian curvature in the boundary layer of the shell plays in dictating shell stability.Multistable structures made with soft materials can reversibly change between stable configurations through a snapthrough elastic instability. Snap-through is a limit point instability [1] that is commonly observed in the eversion of an umbrella on a windy day, or in the jumping of a toy popper [2]. Such structures have utility in engineering and material systems due to their ability to remain in an alternate configuration following the removal of the applied stimulus. Bistable structures have been used in the design of biomedical devices [3], micro-electromechanical systems [4,5], energy harvesters [6,7], morphing structures [8][9][10], and architected materials that trap strain energy [11]. The snap-through of these bistable systems can be triggered by a wide range of stimuli, including temperature [12], light [13] and swelling [14][15][16].Recent research has focused on the snap-through of shells induced by non-mechanical stimuli, such as an evolving natural curvature [16,17]. Such structures often do not possess a stress-free equilibrium configuration, and are therefore modeled using a non-Euclidean shell theory [18]. The critical natural curvature needed to induce snapping of a bistable, stress-free cylindrical shell was recently shown to be proportional to the shell's initial curvature [17]. The snap-through of prestressed cylindrical shells in response to a mechanical force is commonly encountered in structures such as tape springs, tape measures, and toy snap-bracelets [19], but little is understood about the response of these shells to non-mechanical stimuli. Non-mechanical loading of prestressed shells is particularly relevant to electrically active polymers (EAP) wherein dielectric elastomers are deformed in response to an applied voltage [20].The voltage-induced stretching of EAPs is inversely proportional to the material's thickness [21], which has led researchers to significantly prestretch the nearly incompressible d...

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confidence: 99%

Snapping of bistable, prestressed cylindrical shells

Jiang¹,

Pezzulla²,

Shao³

et al. 2018

EPL

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“…), and mechanical properties (Young's modulus, etc.). Some of these properties can be tuned by introducing functional groups that react to different stimuli, [51] by formulating composites to enhance performance, [52][53][54] and by tuning the mechanical properties to vary the output strain. [55] Once the material and stimulant are chosen, the next step is to assemble the materials into functional structures to scale, direct, and distribute the force and displacement.…”

Section: The Design Process For Soft Actuatorsmentioning

confidence: 99%

Section: Manmade Soft Actuatorsmentioning

confidence: 99%

Bioinspired Structures for Soft Actuators

Wei

Ghosh

2022

Adv Materials Technologies

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biological energy into mechanical output. In addition to the actively controlled actuation behavior, plants also produce passive motions driven by the swelling and drying of cellulose materials on the cell walls under the ambient moisture change. [3] These cell-level actuators are shaped, assembled, and structured with other components hierarchically, determining their macroscopic actuation performance. From the mechanical point of view, the actuation behaviors are governed by the stress and strain distribution at various levels of the structure composed of well-arranged active components and supportive matrices. The opening of a pinecone best manifests this principle to release seeds at low humidity conditions. [4] Consisting of two macroscopic layers of tissues with different coefficients of hygroscopic swelling, the scales of pinecone bend outward as the outer layer shrinks more significantly under decreasing humidity. Interestingly, the swelling ability of the two layers is governed at the cellular level, as the special cellulose fibril arrangements on the cell walls effectively modify the stiffness of the cells. While bioinspiration aims to reproduce a functional outcome by drawing on ideas from nature or understanding the principles that underlie natural processes, biomimicry seeks to replicate the mechanism underlying the specific functional behavior found in nature. Notwithstanding the subtle distinction, understanding the fundamentals of biological functions allows us to appreciate why cells and organisms have the structures they do and provides clues to create synthetic systems. Structural design solutions in nature have always been a source of inspiration for scientists and engineers to advance their fields, such as robust yet resilient mechanical structures, [5] biomimetic functional textiles, [6] dry adhesives, [7] drag reduction surfaces, [8] etc. Given that actuation is essential for almost all manmade machines to accomplish their designed functions, scientists are continually looking at every natural environment to find inspiration and ideas to create the new generation of automatons soft robots that can stretch, flex, and morph with high degrees of freedom (DOF). Compared to the conventional rigid actuators such as electric motors, the soft actuators have mechanical properties and actuation behaviors closer to the natural actuators. Therefore, the lessons from nature, particularly the intimate relationship between the structures of biological actuators and their behavior from cellular processes to whole organism functions, provide tremendous insights into designing soft actuators.Biological organisms present marvelous morphing behaviors from the quiescent blooming of flowers to the energetic wing-flapping of birds that have always inspired humans to design better-engineered products. The diversity of natural motion is attributed primarily to the intricate and hierarchical structure of actuators that are self-assembled from nanoscale structures to superstructures. Compared to the biological actuat...

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“…Nevertheless, among all CNT polymer composites, elastomers are among the most studied [71]. Fang et al [72] used dielectric elastomers mixed with highly aligned SWCNTs sheets modified using a laser treatment to induce mechanical anisotropy. During the electrochemical actuation, this treatment showed an appreciable beneficial effect reaching a strain of up to 33%.…”

Section: Carbon Nanotube-based Actuatorsmentioning

confidence: 99%

Carbon Nanostructures for Actuators: An Overview of Recent Developments

Giorcelli

Bartoli

2019

Actuators

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In recent decades, micro and nanoscale technologies have become cutting-edge frontiers in material science and device developments. This worldwide trend has induced further improvements in actuator production with enhanced performance. A main role has been played by nanostructured carbon-based materials, i.e., carbon nanotubes and graphene, due to their intrinsic properties and easy functionalization. Moreover, the nanoscale decoration of these materials has led to the design of doped and decorated carbon-based devices effectively used as actuators incorporating metals and metal-based structures. This review provides an overview and discussion of the overall process for producing AC actuators using nanostructured, doped, and decorated carbon materials. It highlights the differences and common aspects that make carbon materials one of the most promising resources in the field of actuators.

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Enhanced anisotropic response of dielectric elastomer actuators with microcombed and etched carbon nanotube sheet electrodes

Cited by 23 publications

References 35 publications

Snapping of bistable, prestressed cylindrical shells

Snapping of bistable, prestressed cylindrical shells

Bioinspired Structures for Soft Actuators

Carbon Nanostructures for Actuators: An Overview of Recent Developments

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