Eder-Goy, Dagmar (2019)
Numerical Studies on the Influence of Dissipative Effects on Electromechanical Properties of Dielectric Polymers.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
Dielectric polymers find an increased interest in research and development due to an intensive demand of soft and flexible materials for electromechanical components. Dielectric polymers are excellent energy converters because of high efficiency and energy density and have a vast area of application; primarily, they are used in sensors and actuators. Due to tissue-like deformation properties, they are applied for artificial muscles, prosthesis or implants, and are suitable for wearable and foldable electronics. In this work, the viscoelastic behaviour of dielectric polymers is focussed, the frequently investigated acrylic elastomer VBH49, which shows a pronounced viscous deformation, was chosen as material example. A rectangular, dielectric elastomer membrane with compliant electrodes was selected as an example for an actuator. Static and dynamic, voltage-controlled deformation of this idealised dielectric elastomer actuator (DEA) is investigated numerically. Moreover, a global, structural failure mode called “Pull-in instability“ is examined with regard to pre-stretch and viscous effects. The Euler-Lagrange formalism is used at this to obtain equation of motion and viscous evolution equation. Using an energy approach, a stability analysis is conducted to determine the critical parameters for instantaneous and time-delayed dynamic Pull-in. The impact of cross-linking on dynamic deformation is investigated using a viscoelastic Arruda-Boyce material. Continuum mechanical models for electro-viscoelastic behaviour of solid dielectrics, based on a coupling of electrostatic and mechanical stress, are formulated and implemented for small and large deformation applying the Hooke and St.Vernant material law. Numerical solutions for a split of energy function and deformation gradient into elastic and viscoelastic fractions are investigated in reference to a similar split of the stress tensor. Benchmark tests are carried out to validate the models. Non-polar dielectric polymers are used for the manufacturing of pseudo-piezoelectric structures denoted as ferro- or piezoelectrets. Ferroelectrets show piezo- and inverse piezoelectric properties after an electric poling, whereby charge is trapped in the interface of layers with different susceptibility. In this work, ferroelectret structures consisting of air-filled polymer cells from fluorinated ethylene propylene (FEP) are investigated. In contrast to piezoceramics, these ferroelectrets are flexible and allow large deformation; due to their ultra-softness they are suitable for applications activated by sound or vibration. The micro-cellular ferroelectret structures, with measured d33 piezoelectric coefficients up to 160 pCN−1, are analysed by means of Finite-Element simulation. A volume interface element is formulated therefore to map the charging process and the behaviour under compression. The influence of geometry and mechanical boundary conditions on the effective Young’s modulus and the d33 coefficient is studied using a linear model. Electrical and mechanical field distributions are analysed finally for three geometries that either replicate a real cell structure, a simple rectangular structure, or a structure gained from the simulation of FEP-tube compression.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2019 | ||||
Autor(en): | Eder-Goy, Dagmar | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Numerical Studies on the Influence of Dissipative Effects on Electromechanical Properties of Dielectric Polymers | ||||
Sprache: | Englisch | ||||
Referenten: | Xu, Prof. Baixiang ; Gross, Prof. Dietmar | ||||
Publikationsjahr: | 31 Oktober 2019 | ||||
Ort: | Darmstadt | ||||
Datum der mündlichen Prüfung: | 4 Juni 2019 | ||||
URL / URN: | https://tuprints.ulb.tu-darmstadt.de/9220 | ||||
Kurzbeschreibung (Abstract): | Dielectric polymers find an increased interest in research and development due to an intensive demand of soft and flexible materials for electromechanical components. Dielectric polymers are excellent energy converters because of high efficiency and energy density and have a vast area of application; primarily, they are used in sensors and actuators. Due to tissue-like deformation properties, they are applied for artificial muscles, prosthesis or implants, and are suitable for wearable and foldable electronics. In this work, the viscoelastic behaviour of dielectric polymers is focussed, the frequently investigated acrylic elastomer VBH49, which shows a pronounced viscous deformation, was chosen as material example. A rectangular, dielectric elastomer membrane with compliant electrodes was selected as an example for an actuator. Static and dynamic, voltage-controlled deformation of this idealised dielectric elastomer actuator (DEA) is investigated numerically. Moreover, a global, structural failure mode called “Pull-in instability“ is examined with regard to pre-stretch and viscous effects. The Euler-Lagrange formalism is used at this to obtain equation of motion and viscous evolution equation. Using an energy approach, a stability analysis is conducted to determine the critical parameters for instantaneous and time-delayed dynamic Pull-in. The impact of cross-linking on dynamic deformation is investigated using a viscoelastic Arruda-Boyce material. Continuum mechanical models for electro-viscoelastic behaviour of solid dielectrics, based on a coupling of electrostatic and mechanical stress, are formulated and implemented for small and large deformation applying the Hooke and St.Vernant material law. Numerical solutions for a split of energy function and deformation gradient into elastic and viscoelastic fractions are investigated in reference to a similar split of the stress tensor. Benchmark tests are carried out to validate the models. Non-polar dielectric polymers are used for the manufacturing of pseudo-piezoelectric structures denoted as ferro- or piezoelectrets. Ferroelectrets show piezo- and inverse piezoelectric properties after an electric poling, whereby charge is trapped in the interface of layers with different susceptibility. In this work, ferroelectret structures consisting of air-filled polymer cells from fluorinated ethylene propylene (FEP) are investigated. In contrast to piezoceramics, these ferroelectrets are flexible and allow large deformation; due to their ultra-softness they are suitable for applications activated by sound or vibration. The micro-cellular ferroelectret structures, with measured d33 piezoelectric coefficients up to 160 pCN−1, are analysed by means of Finite-Element simulation. A volume interface element is formulated therefore to map the charging process and the behaviour under compression. The influence of geometry and mechanical boundary conditions on the effective Young’s modulus and the d33 coefficient is studied using a linear model. Electrical and mechanical field distributions are analysed finally for three geometries that either replicate a real cell structure, a simple rectangular structure, or a structure gained from the simulation of FEP-tube compression. |
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URN: | urn:nbn:de:tuda-tuprints-92201 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau | ||||
Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > Fachgebiet Mechanik Funktionaler Materialien |
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Hinterlegungsdatum: | 10 Nov 2019 20:55 | ||||
Letzte Änderung: | 10 Nov 2019 20:55 | ||||
PPN: | |||||
Referenten: | Xu, Prof. Baixiang ; Gross, Prof. Dietmar | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 4 Juni 2019 | ||||
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