1,720,964 research outputs found
Instabilities in dielectric elastomers: buckling, wrinkling, and crumpling
No full textInstabilities in a thin sheet are ubiquitous and can be induced by various stimuli, such as a uniaxial force, liquid–vapor surface tension, etc. This paper investigates voltage-induced instabilities in a membrane of a dielectric elastomer. Instabilities including buckling, wrinkling, and crumpling are observed in the experiments. The prestretches of the dielectric elastomer are found to play a significant role in determining its instability mode. When the prestretch is small, intermediate, or large, the membrane may undergo buckling, wrinkling, or crumpling, respectively. Finite element analysis is conducted to study these instability modes, and the simulations are well consistent with the experimental observations. We hope that this investigation of mechanical and physical properties of dielectric elastomers can enhance their extensive and significant applications in soft devices and soft robots
Giant voltage-induced deformation of a dielectric elastomer under a constant pressure
No full textDielectric elastomer actuators coupled with liquid have recently been developed as soft pumps, soft lenses, Braille displays, etc. In this paper, we investigate the performance of a dielectric elastomer actuator, which is coupled with water. The experiments demonstrate that the membrane of a dielectric elastomer can achieve a giant voltage-induced area strain of 1165%, when subject to a constant pressure. Both theory and experiment show that the pressure plays an important role in determining the electromechanical behaviour. The experiments also suggest that the dielectric elastomer actuators, when coupled with liquid, may suffer mechanical instability and collapse after a large amount of liquid is enclosed by the membrane. This failure mode needs to be taken into account in designing soft actuators
A dielectric elastomer actuator coupled with water: snap-through instability and giant deformation
No full textAn electronically tunable duct silencer using dielectric elastomer actuators
No full textA duct silencer with tunable acoustic characteristics is presented in this paper. Dielectric elastomer, a smart material with lightweight, high elastic energy density and large deformation under high direct current/alternating current voltages, was used to fabricate this duct silencer. The acoustic performances and tunable mechanisms of this duct silencer were experimentally investigated. It was found that all the resonance peaks of this duct silencer could be adjusted using external control signals without any additional mechanical part. The physics of the tunable mechanism is further discussed based on the electro-mechanical interactions using finite element analysis. The present promising results also provide insight into the appropriateness of the duct silencer for possible use as next generation acoustic treatment device to replace the traditional acoustic treatment
Modeling of an origami robot driven by electrostatic forces
No full textOrigami is an interesting methodology for developing soft devices, machines and robots. We have developed an origami robot in our previous work, which is driven by electrostatic forces. This robot exhibited interesting attributes of simple structure, light weight, and low cost. A model is expected to play a significant role in interpreting its behavior and improving its performance. In this paper, we illustrate a dynamic model to analyze this origami robot’s motion. The finite element method is first employed to simulate the electrostatic forces among non-parallel deformable plates. A multi-body dynamic model is then developed to interpret the mechanism of this origami robot. The material and structural parameters are calibrated, the forces are analyzed (including the electrostatic forces, inertia forces, frictions, etc), and the robot’s dynamic behaviors are finally predicted. The calculations are well consistent with the experimental results
The mechanism for large-volume fluid pumping via reversible snap-through of dielectric elastomer
No full textGiant deformation of dielectric elastomers (DEs) via electromechanical instability (or the “snap-through” phenomenon) is a promising mechanism for large-volume fluid pumping. Snap-through of a DE membrane coupled with compressible air has been previously investigated. However, the physics behind reversible snap-through of a DE diaphragm coupled with incompressible fluid for the purpose of fluid pumping has not been well investigated, and the conditions required for reversible snap-through in a hydraulic system are unknown. In this study, we have proposed a concept for large-volume fluid pumping by harnessing reversible snap-through of the dielectric elastomer. The occurrence of snap-through was theoretically modeled and experimentally verified. Both the theoretical and experimental pressure-volume curves of the DE membrane under different actuation voltages were used to design the work loop of the pump, and the theoretical work loop agreed with the experimental work loop. Furthermore, the feasibility of reversible snap-through was experimentally verified, and specific conditions were found necessary for this to occur, such as a minimum actuation voltage, an optimal range of hydraulic pressure exerted on the DE membrane and a suitable actuation frequency. Under optimal working conditions, we demonstrated a pumping volume of up to 110 ml per cycle, which was significantly larger than that without snap-through. Furthermore, we have achieved fluid pumping from a region of low pressure to another region of high pressure. Findings of this study would be useful for real world applications such as the blood pump
RATIONAL DESIGN OF MECHANICAL METAMATERIAL STRUCTURES FOR SOFT COMFORMABLE SENSORS AND ACTUATORS
No full textPh.DDOCTOR OF PHILOSOPHY (CDE-ENG
Energy absorption characteristics of sandwich structures subjected to low-velocity impact
No full textThis dissertation presents experimental, numerical and analytical investigations of sandwich plates subjected to quasi-static loading and low-velocity impact. The objectives of this research are to predict the low-velocity impact response and damage in a sandwich structure, and to characterise the energy absorbed by the structure. Aluminium sandwich plates and composite sandwich plates made of Nomex honeycombs and carbon/epoxy skins were investigated under both static indentation and low-velocity impact loadings using a hemispherical indentor/impactor. Emphasis was placed on the damage characteristics and the energy absorption capabilities of these structures. Based on the least-squares method, a single equation that links absorbed energy with the impact energy and the damage initiation threshold energy was derived for composite sandwich plates. It was found that the proportion of impact energy absorbed by the composite plate was inversely related to the damage initiation energy, but directly related to the relative loss of the plate’s transverse stiffness after damage. This energy equation is useful for further studies on damage resistance and tolerance. A three-dimensional FE model was also developed to simulate the indentation and impact tests. In contrast to the equivalent continuum core normally used by other investigators, the cellular honeycomb core was discretely modelled with shell elements so that it was geometrically more accurate. A progressive damage model was also included to predict damage initiation and progression in the laminated skins. Comparison of numerical results with test results demonstrated the ability of the model to capture the impact characteristics. Core damage was identified to be one of the damage mechanisms at initial damage. Parametric studies also showed that denser cores resulted in greater peak loads and smaller damage profiles in the impacted structure. However, the energy absorbed during impact was independent of the core density. Finally, an analytical model was proposed to predict the impact response of a sandwich structure beyond the onset of damage. Closed-form solutions were derived for three
parameters that described the plate’s structural behaviour, namely, the plate’s elastic structural stiffness, the critical load at the onset of damage, and the reduced stiffness after damage. The critical load was found to be theoretically predictable by accounting for the elastic energies absorbed by the sandwich plate up to core failure. These parameters were then included in a modified energy-balance model coupled with the law of conservation of momentum to predict transient load and deflection histories for the plate subjected to impact. This impact model is an efficient design tool which can complement detailed FE simulations.DOCTOR OF PHILOSOPHY (MAE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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