Department of Mechanical Engineering

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Electrically driven dielectric elastomers (DEs) suffer from an electromechanical instability (EMI) when the applied potential difference reaches a critical value. A majority of the past investigations address the mechanics of this operational instability by restricting the kinematics to homogeneous deformations. However, a DE membrane comprising both active and inactive electric regions undergoes inhomogeneous deformation, thus necessitating the solution of a complex boundary value problem. This paper reports the numerical and experimental investigation of such DE actuators with a particular emphasis on the EMI in quasistatic mode of actuation. The numerical simulations are performed using an in-house finite element framework developed based on the field theory of deformable dielectrics. Experiments are performed on the commercially available acrylic elastomer (VHB 4910) at varying levels of prestretch and proportions of the active to inactive areas. In particular, two salient features associated with the electromechanical response are addressed: the effect of the flexible boundary constraint and the locus of the dielectric breakdown point. To highlight the influence of the flexible boundary constraint, the estimates of the threshold value of potential difference on the onset of electromechanical instability are compared with the experimental observations and with those obtained using the lumped parameter models reported previously. Additionally, a locus of localized thinning, near the boundary of the active electric region, is identified using the numerical simulations and ascertained through the experimental observations. Finally, an approach based on the Airy stress function is suggested to justify the phenomenon of localized thinning leading to the dielectric breakdown. © 2019 by ASME.

World University root node

Journal of Applied Mechanics, Transactions ASME

Electromechanical Instability of Dielectric Elastomer Actuators with Active and Inactive Electric Regions

A micromechanical framework is proposed to investigate the effective mechanical properties of elastic two-phase composites with randomly dispersed inhomogeneities in the form of continuous fibres. In this study, an algorithm is developed to generate the microstructure of unidirectional fibre reinforced composite through a three dimensional RVE approach. Using this approach, both regular and random fibre distributions with both undistorted and distorted cross sections are considered and then analysed using mathematical theory of homogenization to estimate the homogenized or effective material properties. Here, RVEs are modeled with random fibre distribution maintaining a fibre volume fraction of 0.6 but increasing the number of fibres gradually and also randomly varying their positions. Finally, the effect of the variation of local volume fraction is studied through master RVE using the moving window technique. The variation in the predicted elastic properties for the given volume fraction for the above-mentioned scenarios is compared with the experimental values. The study shows that results from RVE with more number of random fibres arrangement with geometric cross sectional variations approach the experimental values. However, there is a significant percentage difference in transverse shear moduli, G23 and ν23, of about 22% and 35%, respectively with respect to the experimental results for the scenarios with random fibre distribution. Further, about 16% difference in axial modulus E1 is seen when the effects of local volume fractions are studied. © 2019 Elsevier Ltd

Composite Structures

A micromechanical study and uncertainty quantification for effective properties of unidirectional fibre reinforced composites

This paper addresses a robust motion control design of a planar 1P-2P RP hybrid manipulator for performing the lower limb rehabilitation treatments. The effectiveness and performances of the proposed system along with the motion control scheme is demonstrated using the real-time experiments. Further the robustness and sensitivity of the proposed control scheme is analyzed under different working conditions. In addition, the applicability of the proposed system is demonstrated successfully on an in-house fabricated prototype as a continuous passive sitting type lower limb rehabilitation mechanism in terms of clinical gait pattern generation and the gait-tracking task. © 2018, Springer Nature B.V.

Journal of Intelligent and Robotic Systems: Theory and Applications

Design and Robust Motion Control of a Planar 1P-2P RP Hybrid Manipulator for Lower Limb Rehabilitation Applications

In the present work, we propose an analytical model for the static and DC dynamic pull-in analysis of electrostatically actuated, initially curled microcantilever beams. The analytical model of the initially deformed microcantilever beam incorporates the effects of flexible boundary conditions, fringing fields, and full-order electrostatic nonlinearity. The problem is formulated based on the Euler–Bernoulli theory with slender beams. The pull-in parameters are extracted by incorporating a single mode in the setting of the Galerkin based reduced order model. The effect of the flexible support on the natural frequencies and mode shapes is presented. The parabolic and linear configurations of initial deformation of the beam are assumed for analysis. The accuracy of the present model for static pull-in is verified with the previously reported experimental results. An excellent agreement of the present results with experimental results from the literature indicates the sufficient accuracy of the present model. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.

Microsystem Technologies

Static and DC dynamic pull-in analysis of curled microcantilevers with a compliant support

We report evaporation characteristics due to higher heating from above from surfaces having an array of line sources. The line sources are created by vertically stacked rectangular plates in a box with water. Two different types of plates were used. In one case line source or film thickness was 66 µm and open area ratio was 4%, and in the second case film thickness was 28 µm and 20% was the open area ratio. Even at the 4% open area ratio the evaporation rate was ∼85% compared to a bare water surface, at the same heat flux. Lateral conduction of heat from the impervious hotter regions to the line sources and the 2-D nature of diffusion near these tiny line sources enhances the evaporative flux, owing to increase in the concentration gradient of water vapour, explains the high evaporation rate, observed in the present work. This system bridges the gap between the understanding of evaporation from bare water surfaces (1-D vapour diffusion) and leaf surfaces (3-D vapour diffusion). Evaporation rates for the fully saturated conditions are in good agreement with the theoretical predictions of Suzuki and Maeda (1968) and Schlünder (1988). The computed surface temperatures and its width-wise variation match well with the experimental values. We also propose a simple film model for the unsaturated condition of the porous medium and show that the temperature distribution obtained using this model is in reasonably good agreement with the measured values. © 2019 Elsevier B.V.

Journal of Hydrology

Experimental and numerical investigation of evaporation from line sources of water in low porosity surfaces

Parallel manipulators are being used extensively to cater to the needs of a multitude of industrial automation applications. Due to its kinematic accuracy and structural stiffness, parallel manipulators have proven considerable advantage over their serial counterparts. In modern applications, humans train, collaborate and interact with the manipulators in order to maximize the productivity and the quality of the final product. The critical factor in this human-robot interaction is safety and the ability of the mechanism to comply with human intentions. It thus becomes a necessity for the manipulator to detect external disturbances and interactions, and be able to react accordingly. In this research, a methodology for sensor-less full body active compliance is proposed on a 6-DOF RSS (Rotary-Spherical-Spherical) parallel manipulator. By using the proposed approach, the manipulator can detect and comply with the external forces on any part of its body without using any explicit force/torque sensor at the joint or the end-effector. This is done by utilizing the estimated joint torque based on the actuator current feedback only. A three-layer cascaded impedance controller for active compliance and reaction to various human interactions are reported. The proposed design and unique methodology for compliance exhibits an effective and inexpensive yet reliable alternative to be used in safe human-robot interactions and force controlled manufacturing applications. © 2019

Robotics and Computer-Integrated Manufacturing

Sensorless full body active compliance in a 6 DOF parallel manipulator

Accurate information of inertial parameters is critical to motion planning and control of space robots. Before the launch, only a rudimentary estimate of the inertial parameters is available from experiments and CAD models. After the launch, on-orbit operations substantially alter the value of inertial parameters. In this work, a new momentum model-based method is proposed for identifying the minimal parameters of a space robot while on orbit. Minimal parameters are combinations of the inertial parameters of the links and uniquely define the momentum and dynamic models. Consequently, they are sufficient for motion planning and control of both the satellite and robotic arms mounted on it. The key to the proposed framework is the unique formulation of the momentum model in the linear form of minimal parameters. Further, to estimate the minimal parameters, a novel joint trajectory planning and optimization technique based on direction combinations of joints' velocity are proposed. The efficacy of the identification framework is demonstrated on a 12-degree-of-freedom, spatial, dual-arm space robot. The methodology is developed for tree-type space robots, requires just the pose and twist data, and is scalable with increasing number of joints. Copyright © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Fulltext

Journal of Guidance, Control, and Dynamics

Momentum model-based minimal parameter identification of a space robot

Wireless sensing is a state-of-the-art technology of acquiring information about a remote object and its characteristics without bringing into physical contact with it. Humans have various sensory systems, viz., vision, hear, and smell to observe the object from the remote in day-to-day life. The data from the surrounding can be acquired by means of acoustic waves, distribution of forces, and electromagnetic energy. The collected data can be analyzed to obtain useful information about the object and its characteristics. Swift progress in the microelectronics has resulted in faster response and accurate mode of signal detection. Keeping the technological progress in mind, this article discusses the fundamentals aspects and reviews the state of the artwork on wireless detection technology. © 2019, Springer Nature Singapore Pte Ltd.

Energy, Environment, and Sustainability

Wireless Sensing Systems: A Review

The influence of gap between the cathode and anode over electrodeposition profile was investigated using both the experimental and simulation techniques. Experiments were performed through deposition of copper on stainless steel substrates while varying the electrode distance with a constant applied voltage. Pulse current waveform with 70% duty cycle was applied for better uniform deposition. Complementary 3D model was developed to simulate the effect of electrode distance on current density distribution and thickness of deposition with COMSOL Multiphysics 5.3a. For the chosen experimental conditions, an optimum inter-electrode distance of 60 mm was identified for maximum deposition and good surface morphology. In spite of the application of pulsed current waveform, some amount of non-uniformity was encountered due to edge effect. Inter-electrode gap was demonstrated to be an important factor influencing the deposition profile by correlating experiments with simulation. © Published under licence by IOP Publishing Ltd.

IOP Conference Series: Materials Science and Engineering

Investigations on the effect of electrode gap variation over pulse-electrodeposition profile

The bimetallic welds between ferritic low alloy steels and austenitic stainless steels are widely used in the heat piping transport systems of nuclear power plants for connecting the heavy section low alloy steel components with those of high temperature stainless steel pipes. The operating experience of major nuclear power plant components has recently shown that bimetallic joints can jeopardize the plant availability and safety because of increased incidences of failure. In shielded metal arc welding process, the occurrence and severity of weld defects mainly depend upon the type of electrode filler wire and the electrode coating ingredients used. The use of nickel based filler metals is no longer considered as the final solution for unexpected failures of bimetallic welds due to incidences of hot cracking. In the present paper, an attempt has been made to design and develop an intermediate electrode based on CaO–CaF2–SiO2 ternary phase diagram system and nickel as an additional electrode coating ingredient using mild steel as a filler wire for the bimetallic weld joint. The extreme vertices methodology has been used to design 21 electrode coating formulations. The quadratic regression models for weld metal chemistry, ultimate tensile strength, impact toughness, macrohardness, diffusible hydrogen content, and corrosion rate in terms of electrode coating ingredients, have been developed and checked for adequacy using analysis of variance. The work aims at studying the individual as well as combined effect of electrode coating ingredients on the measured weld responses and microstructures of the weld. Also, the electrode coating formulations suggesting multiobjective optimized solutions have been proposed. © IMechE 2016.