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Gunnar Possart

Bio: Gunnar Possart is an academic researcher from University of Erlangen-Nuremberg. The author has contributed to research in topics: Curing (chemistry) & Finite element method. The author has an hindex of 11, co-authored 24 publications receiving 709 citations. Previous affiliations of Gunnar Possart include Kaiserslautern University of Technology.

Papers
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TL;DR: In this article, the authors reviewed fourteen representatives of these models and derived analytical stress-stretch relations for certain homogeneous deformation modes and summarised the details required for stress tensors and consistent tangent operators.
Abstract: Rubber-like materials consist of chain-like macromolecules that are more or less closely connected to each other via entanglements or cross-links As an idealisation, this particular structure can be described as a completely random three-dimensional network To capture the elastic and nearly incompressible mechanical behaviour of this material class, numerous phenomenological and micro-mechanically motivated models have been proposed in the literature This contribution reviews fourteen selected representatives of these models, derives analytical stress–stretch relations for certain homogeneous deformation modes and summarises the details required for stress tensors and consistent tangent operators The latter, although prevalently missing in the literature, are indispensable ingredients in utilising any kind of constitutive model for the numerical solution of boundary value problems by iterative approaches like the Newton–Raphson scheme Furthermore, performance and validity of the models with regard to the classical experimental data on vulcanised rubber published by Treloar (Trans Faraday Soc 40:59–70, 1944) are evaluated These data are here considered as a prototype or worst-case scenario of highly nonlinear elastic behaviour, although inelastic characteristics are clearly observable but have been tacitly ignored by many other authors

260 citations

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TL;DR: In this paper, a variational formulation of non-linear electroelasticity is proposed and the finite element method is employed to solve the nonlinear electro-mechanical coupling problem.
Abstract: The numerical modelling of non-linear electroelasticity is presented in this work. Based on well-established basic equations of non-linear electroelasticity a variational formulation is built and the finite element method is employed to solve the non-linear electro-mechanical coupling problem. Numerical examples are presented to show the accuracy of the implemented formulation. Copyright © 2006 John Wiley & Sons, Ltd.

189 citations

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TL;DR: In this article, a phenomenological model is presented to describe the curing process of thermosets undergoing small strain deformations, which is a very complex process involving a series of chemical reactions which result in the conversion of liquid low molecular weight monomer mixtures into highly cross-linked solid macromolecular structures.
Abstract: This contribution presents a newly developed phenomenological model to describe the curing process of thermosets undergoing small strain deformations. The governing equations are derived from a number of physical and chemical presuppositions and details of the numerical implementation within the finite element method are given. The curing of thermosets is a very complex process involving a series of chemical reactions which result in the conversion of liquid low molecular weight monomer mixtures into highly cross-linked solid macromolecular structures. This phase transition from a viscous fluid to a viscoelastic solid can be modelled by a constitutive relation which is based on a temporal evolution of shear modulus and relaxation time. Some numerical examples demonstrate the capability of the model to correctly represent the evolution of elastic and inelastic material properties as well as the volume shrinkage taking place during the curing process.

86 citations

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TL;DR: In this article, a phenomenologically motivated small strain model for the simulation of the curing of polymers is presented, which is independent of the choice of the free energy density, i.e., any phenomenological or micromechanical approach can be used.
Abstract: A phenomenologically motivated small strain model to simulate the curing of thermosets has been developed and discussed in a recently published paper (Hossain et al. in Comput Mech 43(6):769–779, 2009). Inspired by the concepts used there, this follow-up contribution presents an extension towards the finite strain regime. The thermodynamically consistent framework proposed here for the simulation of curing polymers particularly is independent of the choice of the free energy density, i.e. any phenomenological or micromechanical approach can be utilised. Both the governing equations for the curing simulation framework and the necessary details for the numerical implementation within the finite element method are derived. The curing of polymers is a very complex process involving a series of chemical reactions typically resulting in a conversion of low molecular weight monomer solutions into more or less cross-linked solid macromolecular structures. A material undergoing such a transition can be modelled by using an appropriate constitutive relation that is distinguished by prescribed temporal evolutions of its governing material parameters, which have to be determined experimentally. Part I of this work will deal with the elastic framework whereas the following Part II will focus on viscoelastic behaviour and shrinkage effects. Some numerical examples demonstrate the capability of our approach to correctly reproduce the behaviour of curing materials.

74 citations

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TL;DR: In this paper, a new simulation technique is introduced to couple a flexible particle domain as encountered in soft-matter systems and a continuum which is solved by the Finite Element (FE) method.

46 citations


Cited by
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Journal ArticleDOI
Zhigang Suo1
TL;DR: In this paper, the authors present a theory of dielectric elastomers, developed within continuum mechanics and thermodynamics, and motivated by molecular pictures and empirical observations, which couples large deformation and electric potential, and describes nonlinear and nonequilibrium behavior, such as electromechanical instability and viscoelasticity.

838 citations

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TL;DR: In this article, a dielectric elastomer generator is used to convert mechanical energy to electrical energy by using a generator that is susceptible to various modes of failure, including electrical breakdown, electromechanical instability, loss of tension, and rupture by stretch.
Abstract: Mechanical energy can be converted to electrical energy by using a dielectric elastomer generator. The elastomer is susceptible to various modes of failure, including electrical breakdown, electromechanical instability, loss of tension, and rupture by stretch. The modes of failure define a cycle of maximal energy that can be converted. This cycle is represented on planes of work-conjugate coordinates and may be used to guide the design of practical cycles.

318 citations

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TL;DR: In this article, the authors place a dielectric elastomer near the verge of snap-through instability, trigger the instability with voltage, and bend the snapthrough path to avert electric breakdown.
Abstract: Dielectric elastomers are capable of large voltage-induced deformation, but achieving such large deformation in practice has been a major challenge due to electromechanical instability and electric breakdown. The complex nonlinear behavior suggests an important opportunity: electromechanical instability can be harnessed to achieve giant voltage-induced deformation. We introduce the following principle of operation: place a dielectric elastomer near the verge of snap-through instability, trigger the instability with voltage, and bend the snap-through path to avert electric breakdown. We demonstrate this principle of operation with a commonly used experimental setup—a dielectric membrane mounted on a chamber of air. The behavior of the membrane can be changed dramatically by varying parameters such as the initial pressure in the chamber, the volume of the chamber, and the prestretch of the membrane. We use a computational model to analyze inhomogeneous deformation and map out bifurcation diagrams to guide the experiment. With suitable values of the parameters, we obtain giant voltage-induced expansion of area by 1692%, far beyond the largest value reported in the literature.

302 citations

Journal ArticleDOI
Wei Hong1
TL;DR: In this paper, the authors developed a field theory that fully couples the large inelastic deformations and electric fields in deformable dielectrics, which predicts the stability criteria of viscoelastic dielectric and its dependence on loading rate, pre-stress, and relaxation.
Abstract: Dielectric elastomers, as an important category of electroactive polymers, are known to have viscoelastic properties that strongly affect their dynamic performance and limit their applications. Very few models accounting for the effects of both electrostatics and viscoelasticity exist in the literature, and even fewer are capable of making reliable predictions under general loads and constraints. Based on the principles of non-equilibrium thermodynamics, this paper develops a field theory that fully couples the large inelastic deformations and electric fields in deformable dielectrics. Our theory recovers existing models of elastic dielectrics in the equilibrium limit. The mechanism of instantaneous instability, which corresponds to the pull-in instability often observed on dielectric elastomers, is studied in a general non-equilibrium state. The current theoretical framework is able to adopt most finite-deformation constitutive relations and evolution laws of viscoelastic solids. As an example, a specific material model is selected and applied to the uniform deformation of a dielectric elastomer. This model predicts the stability criteria of viscoelastic dielectrics and its dependence on loading rate, pre-stress, and relaxation. The dynamic response, as well as the hysteresis behavior of a viscoelastic dielectric elastomer under cyclic electric fields, is also studied.

199 citations

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TL;DR: In this paper, a coarse-grained (CG) potentials obtained via iterative Boltzmann inversion (IBI) were parametrized and validated on polystyrene of 2 kDa (i.e., chains containing 20 monomers).
Abstract: Silica nanoparticles (NPs) embedded in atactic polystyrene (PS) are simulated using coarse-grained (CG) potentials obtained via iterative Boltzmann inversion (IBI) The potentials are parametrized and validated on polystyrene of 2 kDa (ie, chains containing 20 monomers) It is shown that the CG potentials are transferable between different systems The structure of the polymer chains is strongly influenced by the NP Layering, chain expansion, and preferential orientation of segments as well as of entire chains are found The extent of the structural perturbation depends on the details of the system: bare NPs vs NPs grafted with PS chains, grafting density (0, 05, and 1 chains/nm2), length of the grafted chains (2 and 8 kDa), and the matrix chains (2–20 kDa) For example, there is a change in the swelling state for the grafted corona (8 kDa, 1 chains/nm2), when the matrix polymer is changed from 2 to > 8 kDa This phenomenon, sometimes called “wet brush to dry brush transition”, is in good agreement wi

171 citations