In this work, a three dimensional orthotropic viscoelastic material model is implemented in a Matlab program written in the framework of the scaled boundary isogeometric analysis (SBIGA) to simulate electroactive paper (EAPap) actuation behavior. Electroactive papers are smart elastomeric materials which have often been named artificial muscles due to their operational similarities to biological muscles. They consist of a layered fiber oriented cellulose sheet, injected with metallic ions and coated with ultra-thin metallic electrodes on both sides. EAPap are characterized by an electromechanical actuation behavior that consists in generating a bending displacement under the application of an electric field between the electrodes. This peculiar property combined with a low mass density, reduced production costs and high sustainability has fostered multiple applications for the material in the field of actuator and sensor devices. The electromechanical coupling is mainly due to an ionic migration through the thickness and it is referred to as actuation behavior. The objective of the current research is the prediction of the viscoelastic response of EAPap, occurring under both mechanical and electromechanical deformation processes. Experimental evidences suggests that the viscous phenomena is intrinsic and dominant, affecting the performances and reliability of EAPap based devices and should be analyzed in the design stage. Therefore, the goal of this thesis it to develop a simple but effective numerical tool to simulate the viscoelastic response of EAPap and to be used for the design of new devices, especially when operational conditions provide for high temperature or humidity and long-term loading. To predict the viscous creep and relaxation responses, the 3D viscoelastic constitutive law in rheological differential form is implemented. Multiple material representations are proposed and compared: the Kelvin-Voigt model and standard linear solid models in Maxwell and Jeffreys forms. To complete the elastic modeling accounting for material anisotropy, the general 3D orthotropic constitutive law is also implemented. Finally, the electromechanical coupling is established by means of a phenomenological model defining a mechanical volume force density which depends on the ionic charge distribution through the thickness of the actuator. Subsequently, the algorithm is validated with standard benchmark problems of traction and bending of plates. To conclude, the program capabilities are demonstrated by simulating viscoelastic mechanical and electromechanical experimental tests in literature performed on EAPap samples. Overall, the numerical results prove excellent qualitative agreement with the experimental measurements and in some cases also good quantitative approximation in engineering terms. Complementary future work could be devoted to the material constants calibration through laboratory tests aiming to a general qualitative numerical solution to be exploited in the viscoelastic design of EAPap devices.
Nel presente lavoro, un modello materiale ortotropico e viscoelastico tridimensionale è implementato in un programma Matlab basto sul metodo agli elementi finiti di contorno scalati con analisi isogeometrica (SBIGA) per simulare l’attuazione a flessione delle carte elettroattive (EAPap: electroactive paper). Gli EAPap sono materiali polimerici “intelligenti” facenti parte della famiglia dei muscoli artificiali, grazie alle funzionalità simili a quelle dei muscoli biologici. Le carte elettroattive sono realizzate da un foglio di cellulosa rigenerata ad orientamento delle fibre migliorato, in cui vengono iniettati ioni metallici e che viene rivestito su ambo i lati da elettrodi ultra sottili. Gli EAPap sono caratterizzati dall’attuazione elettromeccanica, generando uno spostamento a flessione per mezzo dell’applicazione di una differenza di potenziale elettrico tra i due elettrodi. Questa proprietà peculiare, combinata con una bassa densità di massa, un contenuto costo di produzione e un elevata sostenibilità ambientale, ha promosso numerose applicazioni nel campo dei sensori e degli attuatori. L’accoppiamento elettromeccanico è dovuto principalmente ad una migrazione ionica lungo lo spessore dell’attuatore ed è chiamato attuazione. L’oggetto della ricerca è la previsione della risposta viscoelastica degli EAPap, che si verifica durante entrambi i processi di deformazione meccanica ed elettromeccanica. Le evidenze sperimentali suggeriscono che i fenomeni viscosi influenzino le prestazioni e l’affidabilità dei dispositivi a base EAPap e che perciò debbano essere analizzati durante la progettazione. Dunque, l’obiettivo della tesi è sviluppare un semplice ma efficace algoritmo per simulare la viscoelasticità degli EAPap, che possa essere impiegato nella progettazione di nuovi dispositivi; in particolar modo in condizioni di elevata temperatura o umidità e sotto l’azione di carichi a lungo termine. Per simulare il comportamento di creep e rilassamento viscosi, si implementa una legge costitutiva viscoelastica tridimensionale, a partire dai modelli reologici di Kelvin-Voigt e di solido lineare standard nelle forme di Maxwell e di Jeffreys, espressi in forma differenziale. Inoltre, la modellazione elastica viene completata per considerare l’anisotropia implementando una legge costitutiva ortotropica. L’accoppiamento elettromeccanico viene definito da un modello fenomenologico, stabilendo una forza meccanica di volume equivalente al voltaggio applicato. Successivamente, l’algoritmo viene validato tramite la soluzione di problemi standard come la prova a trazione e la flessione delle strutture a piastra. In fine, il programma viene applicato per simulare delle prove sperimentali da letteratura sulla viscoelasticità degli EAPap. In conclusione, le simulazioni numeriche mostrano un buon accordo qualitativo con le prove sperimentali, catturando complessivamente la risposta degli EAPap. Nuove prove di laboratorio permetteranno in futuro di migliorare la calibrazione dei parametri che, unitamente all’arricchimento del modello, consentiranno il raggiungimento di una buona approssimazione quantitativa.
An orthotropic visco-elastic material model for the analysis of electroactive paper actuators
Algeri, Giulio
2019/2020
Abstract
In this work, a three dimensional orthotropic viscoelastic material model is implemented in a Matlab program written in the framework of the scaled boundary isogeometric analysis (SBIGA) to simulate electroactive paper (EAPap) actuation behavior. Electroactive papers are smart elastomeric materials which have often been named artificial muscles due to their operational similarities to biological muscles. They consist of a layered fiber oriented cellulose sheet, injected with metallic ions and coated with ultra-thin metallic electrodes on both sides. EAPap are characterized by an electromechanical actuation behavior that consists in generating a bending displacement under the application of an electric field between the electrodes. This peculiar property combined with a low mass density, reduced production costs and high sustainability has fostered multiple applications for the material in the field of actuator and sensor devices. The electromechanical coupling is mainly due to an ionic migration through the thickness and it is referred to as actuation behavior. The objective of the current research is the prediction of the viscoelastic response of EAPap, occurring under both mechanical and electromechanical deformation processes. Experimental evidences suggests that the viscous phenomena is intrinsic and dominant, affecting the performances and reliability of EAPap based devices and should be analyzed in the design stage. Therefore, the goal of this thesis it to develop a simple but effective numerical tool to simulate the viscoelastic response of EAPap and to be used for the design of new devices, especially when operational conditions provide for high temperature or humidity and long-term loading. To predict the viscous creep and relaxation responses, the 3D viscoelastic constitutive law in rheological differential form is implemented. Multiple material representations are proposed and compared: the Kelvin-Voigt model and standard linear solid models in Maxwell and Jeffreys forms. To complete the elastic modeling accounting for material anisotropy, the general 3D orthotropic constitutive law is also implemented. Finally, the electromechanical coupling is established by means of a phenomenological model defining a mechanical volume force density which depends on the ionic charge distribution through the thickness of the actuator. Subsequently, the algorithm is validated with standard benchmark problems of traction and bending of plates. To conclude, the program capabilities are demonstrated by simulating viscoelastic mechanical and electromechanical experimental tests in literature performed on EAPap samples. Overall, the numerical results prove excellent qualitative agreement with the experimental measurements and in some cases also good quantitative approximation in engineering terms. Complementary future work could be devoted to the material constants calibration through laboratory tests aiming to a general qualitative numerical solution to be exploited in the viscoelastic design of EAPap devices.File | Dimensione | Formato | |
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Descrizione: An orthotropic visco-elastic material model for the analysis of ElectroActive Paper actuators
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https://hdl.handle.net/10589/176032