Materials

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19 pages, 2724 KiB

Open AccessArticle

Suitability of Different Analytical Derivations of Electrically Induced Stress States in Planar and Cylindrical Dielectric Elastomer Actuators

by Sascha Pfeil and Gerald Gerlach

Materials 2022, 15(4), 1321; https://doi.org/10.3390/ma15041321 - 10 Feb 2022

Cited by 2 | Viewed by 1579

Abstract

Dielectric elastomers (DE) belong to a very performant and efficient class of functional materials for actuators, while being compliant, low-weight and silent, they offer high energy efficiencies and large deformations under an applied electric field. In this work, a comparison of different approaches [...] Read more.

Dielectric elastomers (DE) belong to a very performant and efficient class of functional materials for actuators, while being compliant, low-weight and silent, they offer high energy efficiencies and large deformations under an applied electric field. In this work, a comparison of different approaches to derive expressions for the electrically induced stress states in dielectric materials is given. In particular, the focus is on three different ways to analytically describe stress states in planar actuator setups and to show how they are connected to each other regarding their resulting deformations. This is the basis to evaluate the suitability of these approaches for cylindrical actuator geometries together with exemplary calculations for concrete use cases. As an outcome, conclusions on the suitability of the different approaches for certain actuator setups are drawn. In particular cylindrical actuator geometries are taken into account and a recommendation on which approach is useful to describe a certain actuator effect is given. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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14 pages, 2198 KiB

Open AccessArticle

Thermo-Electro-Mechanical Simulation of Electro-Active Composites

by Anas Kanan, Aleksandr Vasilev, Cornelia Breitkopf and Michael Kaliske

Materials 2022, 15(3), 783; https://doi.org/10.3390/ma15030783 - 20 Jan 2022

Cited by 5 | Viewed by 1817

Abstract

In this contribution, a computational thermo-electro-mechanical framework is considered, to simulate coupling between the mechanical, electrical and thermal fields, in nonhomogeneous electro-active materials. A thermo-electro-mechanical material model and a mixed Q1P0 finite element framework are described and used for the simulations. Finite element [...] Read more.

In this contribution, a computational thermo-electro-mechanical framework is considered, to simulate coupling between the mechanical, electrical and thermal fields, in nonhomogeneous electro-active materials. A thermo-electro-mechanical material model and a mixed Q1P0 finite element framework are described and used for the simulations. Finite element simulations of the response of heterogeneous structures consisting of a soft matrix and a stiff incluison are considered. The behavior of the composite material is studied for varying initial temperatures, different volume fractions and various aspect ratios of the inclusion. For some of the examples, the response of the structure beyond a limit point of electro-mechanical instability is traced. Regarding the soft matrix of the composite, thermal properties of silicone rubber at normal conditions have been obtained by molecular dynamics (MD) simulations. The material parameters obtained by MD simulations are used within the finite element simulations. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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23 pages, 7749 KiB

Open AccessEditor’s ChoiceArticle

Experimental and Numerical Analysis of the Deformation Behavior of Adaptive Fiber-Rubber Composites with Integrated Shape Memory Alloys

by Felix Lohse, Karl Kopelmann, Henriette Grellmann, Moniruddoza Ashir, Thomas Gereke, Eric Häntzsche, Cornelia Sennewald and Chokri Cherif

Materials 2022, 15(2), 582; https://doi.org/10.3390/ma15020582 - 13 Jan 2022

Cited by 16 | Viewed by 2544

Abstract

Fiber-reinforced rubber composites with integrated shape memory alloy (SMA) actuator wires present a promising approach for the creation of soft and highly elastic structures with adaptive functionalities for usage in aerospace, robotic, or biomedical applications. In this work, the flat-knitting technology is used [...] Read more.

Fiber-reinforced rubber composites with integrated shape memory alloy (SMA) actuator wires present a promising approach for the creation of soft and highly elastic structures with adaptive functionalities for usage in aerospace, robotic, or biomedical applications. In this work, the flat-knitting technology is used to develop glass-fiber-reinforced fabrics with tailored properties designed for active bending deformations. During the knitting process, the SMA wires are integrated into the textile and positioned with respect to their actuation task. Then, the fabrics are infiltrated with liquid silicone, thus creating actively deformable composites. For dimensioning such structures, a comprehensive understanding of the interactions of all components is required. Therefore, a simulation model is developed that captures the properties of the rubber matrix, fiber reinforcement, and the SMA actuators and that is capable of simulating the active bending deformations of the specimens. After model calibration with experimental four-point-bending data, the SMA-driven bending deformation is simulated. The model is validated with activation experiments of the actively deformable specimens. The simulation results show good agreement with the experimental tests, thus enabling further investigations into the deformation mechanisms of actively deformable fiber-reinforced rubbers. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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12 pages, 4541 KiB

Open AccessEditor’s ChoiceArticle

Integrated Temperature and Position Sensors in a Shape-Memory Driven Soft Actuator for Closed-Loop Control

by Johannes Mersch, Najmeh Keshtkar, Henriette Grellmann, Carlos Alberto Gomez Cuaran, Mathis Bruns, Andreas Nocke, Chokri Cherif, Klaus Röbenack and Gerald Gerlach

Materials 2022, 15(2), 520; https://doi.org/10.3390/ma15020520 - 10 Jan 2022

Cited by 7 | Viewed by 2236

Abstract

Soft actuators are a promising option for the advancing fields of human-machine interaction and dexterous robots in complex environments. Shape memory alloy wire actuators can be integrated into fiber rubber composites for highly deformable structures. For autonomous, closed-loop control of such systems, additional [...] Read more.

Soft actuators are a promising option for the advancing fields of human-machine interaction and dexterous robots in complex environments. Shape memory alloy wire actuators can be integrated into fiber rubber composites for highly deformable structures. For autonomous, closed-loop control of such systems, additional integrated sensors are necessary. In this work, a soft actuator is presented that incorporates fiber-based actuators and sensors to monitor both deformation and temperature. The soft actuator showed considerable deformation around two solid body joints, which was then compared to the sensor signals, and their correlation was analyzed. Both, the actuator as well as the sensor materials were processed by braiding and tailored fiber placement before molding with silicone rubber. Finally, the novel fiber-rubber composite material was used to implement closed-loop control of the actuator with a maximum error of 0.5°. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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14 pages, 3542 KiB

Open AccessArticle

Development of Liquid Diene Rubber Based Highly Deformable Interactive Fiber-Elastomer Composites

by Vikram G. Kamble, Johannes Mersch, Muhammad Tahir, Klaus Werner Stöckelhuber, Amit Das and Sven Wießner

Materials 2022, 15(1), 390; https://doi.org/10.3390/ma15010390 - 5 Jan 2022

Cited by 6 | Viewed by 2635

Abstract

The preparation of intelligent structures for multiple smart applications such as soft-robotics, artificial limbs, etc., is a rapidly evolving research topic. In the present work, the preparation of a functional fabric, and its integration into a soft elastomeric matrix to develop an adaptive [...] Read more.

The preparation of intelligent structures for multiple smart applications such as soft-robotics, artificial limbs, etc., is a rapidly evolving research topic. In the present work, the preparation of a functional fabric, and its integration into a soft elastomeric matrix to develop an adaptive fiber-elastomer composite structure, is presented. Functional fabric, with the implementation of the shape memory effect, was combined with liquid polybutadiene rubber by means of a low-temperature vulcanization process. A detailed investigation on the crosslinking behavior of liquid polybutadiene rubber was performed to develop a rubber formulation that is capable of crosslinking liquid rubber at 75 °C, a temperature that is much lower than the phase transformation temperature of SMA wires (90–110 °C). By utilizing the unique low-temperature crosslinking protocol for liquid polybutadiene rubber, soft intelligent structures containing functional fabric were developed. The adaptive structures were successfully activated by Joule heating. The deformation behavior of the smart structures was experimentally demonstrated by reaching a 120 mm bending distance at an activation voltage of 8 V without an additional load, whereas 90 mm, 70 mm, 65 mm, 57 mm bending distances were achieved with attached weights of 5 g, 10 g, 20 g, 30 g, respectively. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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14 pages, 2846 KiB

Open AccessArticle

Thermo-Electro-Mechanical Characterization of PDMS-Based Dielectric Elastomer Actuators

by Konrad Katzer, Anas Kanan, Sascha Pfeil, Henriette Grellmann, Gerald Gerlach, Michael Kaliske, Chokri Cherif and Martina Zimmermann

Materials 2022, 15(1), 221; https://doi.org/10.3390/ma15010221 - 28 Dec 2021

Cited by 9 | Viewed by 2167

Abstract

The present contribution aims towards a thermo-electro-mechanical characterization of dielectric elastomer actuators (DEA) based on polydimethylsiloxane (PDMS). To this end, an experimental setup is proposed in order to evaluate the PDMS-based DEA behavior under the influence of various rates of mechanical loading, different [...] Read more.

The present contribution aims towards a thermo-electro-mechanical characterization of dielectric elastomer actuators (DEA) based on polydimethylsiloxane (PDMS). To this end, an experimental setup is proposed in order to evaluate the PDMS-based DEA behavior under the influence of various rates of mechanical loading, different ambient temperatures, and varying values of an applied electric voltage. To obtain mechanical, electro-mechanical and thermo-mechanical experimental data, the passive behavior of the material, as well as the material’s response when electrically activated, was tested. The influence of the solid electrode on the dielectric layer’s surface was also examined. Moreover, this work focuses on the production of such DEA, the experimental setup and the interpretation and evaluation of the obtained mechanical hysteresis loops. Finite element modeling approaches were used in order to model the passive and the electro-mechanically active response of the material. A comparison between experimental and simulation results was performed. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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10 pages, 20065 KiB

Open AccessArticle

Thermal Conductivity of Polybutadiene Rubber from Molecular Dynamics Simulations and Measurements by the Heat Flow Meter Method

by Aleksandr Vasilev, Tommy Lorenz, Vikram G Kamble, Sven Wießner and Cornelia Breitkopf

Materials 2021, 14(24), 7737; https://doi.org/10.3390/ma14247737 - 15 Dec 2021

Cited by 9 | Viewed by 2390

Abstract

Thermal conductivities of polybutadiene rubbers crosslinked by 2.4 and 2.8 phr of sulfur have been found to be functions of temperature via molecular dynamics (MD) simulations using the Green–Kubo method. From an analysis of the heat flux autocorrelation functions, it has been revealed [...] Read more.

Thermal conductivities of polybutadiene rubbers crosslinked by 2.4 and 2.8 phr of sulfur have been found to be functions of temperature via molecular dynamics (MD) simulations using the Green–Kubo method. From an analysis of the heat flux autocorrelation functions, it has been revealed that the dominant means of heat transport in rubbers is governed by deformations of polymeric chains. Thermal conductivities of rubber samples vulcanized by 2.4 and 2.8 phr of sulfur have been measured by the heat flow meter method between 0

^{\circ}

C and 60

^{\circ}

C at atmospheric pressure. The temperature dependencies of the thermal conductivities of rubbers and their glass transition temperatures derived from MD simulations are in good agreement with the literature and experimental data. Details are discussed in the paper. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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11 pages, 2481 KiB

Open AccessArticle

Development of an Elastic, Electrically Conductive Coating for TPU Filaments

by Henriette Grellmann, Mathis Bruns, Felix Michael Lohse, Iris Kruppke, Andreas Nocke and Chokri Cherif

Materials 2021, 14(23), 7158; https://doi.org/10.3390/ma14237158 - 24 Nov 2021

Cited by 1 | Viewed by 2507

Abstract

Electrically conductive filaments are used in a wide variety of applications, for example, in smart textiles and soft robotics. Filaments that conduct electricity are required for the transmission of energy and information, but up until now, most electrically conductive fibers, filaments and wires [...] Read more.

Electrically conductive filaments are used in a wide variety of applications, for example, in smart textiles and soft robotics. Filaments that conduct electricity are required for the transmission of energy and information, but up until now, most electrically conductive fibers, filaments and wires offer low mechanical elongation. Therefore, they are not well suited for the implementation into elastomeric composites and textiles that are worn close to the human body and have to follow a wide range of movements. In order to overcome this issue, the presented study aims at the development of electrically conductive and elastic filaments based on a coating process suited for multifilament yarns made of thermoplastic polyurethane (TPU). The coating solution contains TPU, carbon nanotubes (CNT) and N-Methyl-2-pyrrolidone (NMP) with varied concentrations of solids and electrically conductive particles. After applying the coating to TPU multifilament yarns, the mechanical and electrical properties are analyzed. A special focus is given to the electromechanical behavior of the coated yarns under mechanical strain loading. It is determined that the electrical conductivity is maintained even at elongations of up to 100%. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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17 pages, 1095 KiB

Open AccessArticle

Field-Induced Transversely Isotropic Shear Response of Ellipsoidal Magnetoactive Elastomers

by Sanket Chougale, Dirk Romeis and Marina Saphiannikova

Materials 2021, 14(14), 3958; https://doi.org/10.3390/ma14143958 - 15 Jul 2021

Cited by 5 | Viewed by 2757

Abstract

Magnetoactive elastomers (MAEs) claim a vital place in the class of field-controllable materials due to their tunable stiffness and the ability to change their macroscopic shape in the presence of an external magnetic field. In the present work, three principal geometries of shear [...] Read more.

Magnetoactive elastomers (MAEs) claim a vital place in the class of field-controllable materials due to their tunable stiffness and the ability to change their macroscopic shape in the presence of an external magnetic field. In the present work, three principal geometries of shear deformation were investigated with respect to the applied magnetic field. The physical model that considers dipole-dipole interactions between magnetized particles was used to study the stress-strain behavior of ellipsoidal MAEs. The magneto-rheological effect for different shapes of the MAE sample ranging from disc-like (highly oblate) to rod-like (highly prolate) samples was investigated along and transverse to the field direction. The rotation of the MAE during the shear deformation leads to a non-symmetric Cauchy stress tensor due to a field-induced magnetic torque. We show that the external magnetic field induces a mechanical anisotropy along the field direction by determining the distinct magneto-mechanical behavior of MAEs with respect to the orientation of the magnetic field to shear deformation. Full article

(This article belongs to the Special Issue Interactive Fiber Rubber Composites)

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