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Y Alizadeh - One of the best experts on this subject based on the ideXlab platform.
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visco hyperelastic constitutive law for modeling of foam s behavior
Materials & Design, 2011Co-Authors: Yavar Anani, Y AlizadehAbstract:Abstract This paper proposes a new visco-hyperelastic constitutive law for modeling the finite-deformation strain rate-dependent behavior of foams as compressible elastomers. The proposed model is based on a phenomenological Zener model, which consists of a hyperelastic equilibrium spring and a Maxwell Element parallel to it. The hyperelastic equilibrium spring describes the steady state response. The Maxwell Element, which captures the rate-dependency behavior, consists of a nonlinear viscous damper connected in series to a hyperelastic intermediate spring. The nonlinear damper controls the rate-dependency of the Maxwell Element. Some strain energy potential functions are proposed for the two hyperelastic springs. compressibility effect in strain energy is described by entering the third invariant of deformation gradient tensor into strain energy functions. A history integral method has been used to develop a constitutive equation for modeling the behavior of the foams. The applied history integral method is based on the Kaye–BKZ theory. The material constant parameters, appeared in the formulation, have been determined with the aid of available uniaxial tensile experimental tests for a specific material.
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Visco-hyperelastic constitutive law for modeling of foam’s behavior
Materials & Design, 2011Co-Authors: Yavar Anani, Y AlizadehAbstract:Abstract This paper proposes a new visco-hyperelastic constitutive law for modeling the finite-deformation strain rate-dependent behavior of foams as compressible elastomers. The proposed model is based on a phenomenological Zener model, which consists of a hyperelastic equilibrium spring and a Maxwell Element parallel to it. The hyperelastic equilibrium spring describes the steady state response. The Maxwell Element, which captures the rate-dependency behavior, consists of a nonlinear viscous damper connected in series to a hyperelastic intermediate spring. The nonlinear damper controls the rate-dependency of the Maxwell Element. Some strain energy potential functions are proposed for the two hyperelastic springs. compressibility effect in strain energy is described by entering the third invariant of deformation gradient tensor into strain energy functions. A history integral method has been used to develop a constitutive equation for modeling the behavior of the foams. The applied history integral method is based on the Kaye–BKZ theory. The material constant parameters, appeared in the formulation, have been determined with the aid of available uniaxial tensile experimental tests for a specific material.
Yavar Anani - One of the best experts on this subject based on the ideXlab platform.
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Modeling of visco‐hyperelastic behavior of transversely isotropic functionally graded rubbers
Polymer Engineering & Science, 2016Co-Authors: Yavar Anani, G. H. RahimiAbstract:In this article, visco-hyperelastic constitutive model is developed to describe the rate-dependent behavior of transversely isotropic functionally graded rubber-like materials at finite deformations. Zener model that consists of Maxwell Element parallel to a hyperelastic equilibrium spring is used in this article. Steady state response is described by equilibrium hyperelastic spring and rate-dependence behavior is modeled by Maxwell Element that consists of a hyperelastic intermediate spring and a nonlinear viscous damper. Modified and reinforced neo-Hookean strain energy function is proposed for the two hyperelastic springs. The mechanical properties and material constants of strain energy function are graded along the axial direction based on exponential function. A history-integral method has been used to develop a constitutive equation for modeling the behavior of the model. The applied history integral method is based on the Kaye-BKZ theory. The material constant parameters appeared in the formulation have been determined with the aid of available uniaxial tensile experimental tests for a specific material and the results are compared to experimental results. It is then concluded that, the proposed constitutive equation is quite proficient in forecasting the behavior of rubber-like materials in different deformation and wide ranges of strain rate. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers
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visco hyperelastic constitutive law for modeling of foam s behavior
Materials & Design, 2011Co-Authors: Yavar Anani, Y AlizadehAbstract:Abstract This paper proposes a new visco-hyperelastic constitutive law for modeling the finite-deformation strain rate-dependent behavior of foams as compressible elastomers. The proposed model is based on a phenomenological Zener model, which consists of a hyperelastic equilibrium spring and a Maxwell Element parallel to it. The hyperelastic equilibrium spring describes the steady state response. The Maxwell Element, which captures the rate-dependency behavior, consists of a nonlinear viscous damper connected in series to a hyperelastic intermediate spring. The nonlinear damper controls the rate-dependency of the Maxwell Element. Some strain energy potential functions are proposed for the two hyperelastic springs. compressibility effect in strain energy is described by entering the third invariant of deformation gradient tensor into strain energy functions. A history integral method has been used to develop a constitutive equation for modeling the behavior of the foams. The applied history integral method is based on the Kaye–BKZ theory. The material constant parameters, appeared in the formulation, have been determined with the aid of available uniaxial tensile experimental tests for a specific material.
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Visco-hyperelastic constitutive law for modeling of foam’s behavior
Materials & Design, 2011Co-Authors: Yavar Anani, Y AlizadehAbstract:Abstract This paper proposes a new visco-hyperelastic constitutive law for modeling the finite-deformation strain rate-dependent behavior of foams as compressible elastomers. The proposed model is based on a phenomenological Zener model, which consists of a hyperelastic equilibrium spring and a Maxwell Element parallel to it. The hyperelastic equilibrium spring describes the steady state response. The Maxwell Element, which captures the rate-dependency behavior, consists of a nonlinear viscous damper connected in series to a hyperelastic intermediate spring. The nonlinear damper controls the rate-dependency of the Maxwell Element. Some strain energy potential functions are proposed for the two hyperelastic springs. compressibility effect in strain energy is described by entering the third invariant of deformation gradient tensor into strain energy functions. A history integral method has been used to develop a constitutive equation for modeling the behavior of the foams. The applied history integral method is based on the Kaye–BKZ theory. The material constant parameters, appeared in the formulation, have been determined with the aid of available uniaxial tensile experimental tests for a specific material.
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Modeling of Visco-Hyperelastic Behavior of Foams
Volume 12: Mechanics of Solids Structures and Fluids, 2008Co-Authors: Yavar Anani, M. Asghari, R. NaghdabadiAbstract:In this paper, a new visco-hyperelastic constitutive law for describing the rate dependent behavior of foams is proposed. The proposed model was based on a phenomenological Zener model: a hyperelastic equilibrium spring, which describes the steady-state, long-term response, parallel to a Maxwell Element, which captures the ratedependency. A nonlinear viscous damper connected in series to a hyperelastic intermediate spring, controls the ratedependency of the Maxwell Element. Therefore, the stress is the sum of equilibrium stress on the equilibrium spring and overstress on the intermediate spring. In hyperelastic theory stress is not calculated directly as in the case of small-strain, linear elastic materials. Instead, stresses are derived from the principle of virtual work using the stored strain energy potential function. In addition, foams are compressible, therefore classic strain energy functions such as the Ogden strain energy function or the Mooney-Rivlin strain energy function are not suitable to describe hyperelastic behavior of foams. So, strain energy functions must include the effect of compressibility. That means the third principal invariant of the deformation gradient tensor F should enter in strain energy functions. For rate-dependent behavior of foams, history integral constitutive law is used. For the equilibrium spring and the intermediate spring, the same strain energy function is employed. In order to use this stain energy function in history integral equation, the kernel function of it is calculated. The effect of compressibility is considered in rate-dependent behavior of foams too. All material constants were obtained from the results of uniaxial tensile tests. Nonlinear regulation was used to find these constants. In these calculations, Average strain rate was employed to find material constants.Copyright © 2008 by ASME
Helmut Föll - One of the best experts on this subject based on the ideXlab platform.
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FFT-impedance spectroscopy analysis of the growth of magnetic metal nanowires in ultra-high aspect ratio InP membranes
Semiconductor Science and Technology, 2015Co-Authors: Mark-daniel Gerngross, Juergen Carstensen, Helmut Föll, Rainer AdelungAbstract:This paper reports on the characterization of the electrochemical growth process of magnetic nanowires in ultra-high-aspect ratio InP membranes via in situ fast Fourier transform impedance spectroscopy in a typical frequency range from 75 Hz to 18.5 kHz. The measured impedance data from the Ni, Co, and FeCo can be very well fitted using the same electric equivalent circuit consisting of a series resistance in serial connection to an RC-Element and a Maxwell Element. The impedance data clearly indicate the similarities in the growth behavior of Ni, Co and FeCo nanowires in ultra-high aspect ratio InP membranes—the beneficial impact of boric acid on the metal deposition in ultra-high aspect ratio membranes and the diffusion limitation of boric acid, as well as differences such as passivation or side reactions.
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Electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes: FFT-impedance spectroscopy of the growth process and magnetic properties
Nanoscale Research Letters, 2014Co-Authors: Mark-daniel Gerngross, Jürgen Carstensen, Helmut FöllAbstract:The electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes has been investigated by fast Fourier transform-impedance spectroscopy (FFT-IS) in the frequency range from 75 Hz to 18.5 kHz. The impedance data could be fitted very well using an electric circuit equivalent model with a series resistance connected in series to a simple resistor-capacitor ( RC ) Element and a Maxwell Element. Based on the impedance data, the Co deposition in ultra-high aspect ratio InP membranes can be divided into two different Co deposition processes. The corresponding share of each process on the overall Co deposition can be determined directly from the transfer resistances of the two processes. The impedance data clearly show the beneficial impact of boric acid on the Co deposition and also indicate a diffusion limitation of boric acid in ultra-high aspect ratio InP membranes. The grown Co nanowires are polycrystalline with a very small grain size. They show a narrow hysteresis loop with a preferential orientation of the easy magnetization direction along the long nanowire axis due to the arising shape anisotropy of the Co nanowires.
Mark-daniel Gerngross - One of the best experts on this subject based on the ideXlab platform.
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FFT-impedance spectroscopy analysis of the growth of magnetic metal nanowires in ultra-high aspect ratio InP membranes
Semiconductor Science and Technology, 2015Co-Authors: Mark-daniel Gerngross, Juergen Carstensen, Helmut Föll, Rainer AdelungAbstract:This paper reports on the characterization of the electrochemical growth process of magnetic nanowires in ultra-high-aspect ratio InP membranes via in situ fast Fourier transform impedance spectroscopy in a typical frequency range from 75 Hz to 18.5 kHz. The measured impedance data from the Ni, Co, and FeCo can be very well fitted using the same electric equivalent circuit consisting of a series resistance in serial connection to an RC-Element and a Maxwell Element. The impedance data clearly indicate the similarities in the growth behavior of Ni, Co and FeCo nanowires in ultra-high aspect ratio InP membranes—the beneficial impact of boric acid on the metal deposition in ultra-high aspect ratio membranes and the diffusion limitation of boric acid, as well as differences such as passivation or side reactions.
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Electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes: FFT-impedance spectroscopy of the growth process and magnetic properties
Nanoscale Research Letters, 2014Co-Authors: Mark-daniel Gerngross, Jürgen Carstensen, Helmut FöllAbstract:The electrochemical growth of Co nanowires in ultra-high aspect ratio InP membranes has been investigated by fast Fourier transform-impedance spectroscopy (FFT-IS) in the frequency range from 75 Hz to 18.5 kHz. The impedance data could be fitted very well using an electric circuit equivalent model with a series resistance connected in series to a simple resistor-capacitor ( RC ) Element and a Maxwell Element. Based on the impedance data, the Co deposition in ultra-high aspect ratio InP membranes can be divided into two different Co deposition processes. The corresponding share of each process on the overall Co deposition can be determined directly from the transfer resistances of the two processes. The impedance data clearly show the beneficial impact of boric acid on the Co deposition and also indicate a diffusion limitation of boric acid in ultra-high aspect ratio InP membranes. The grown Co nanowires are polycrystalline with a very small grain size. They show a narrow hysteresis loop with a preferential orientation of the easy magnetization direction along the long nanowire axis due to the arising shape anisotropy of the Co nanowires.
Michael Kaliske - One of the best experts on this subject based on the ideXlab platform.
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Comparison of approaches to model viscoelasticity based on fractional time derivatives
Computational Materials Science, 2015Co-Authors: Christoph Zopf, S.e. Hoque, Michael KaliskeAbstract:Abstract Two approaches to describe a constitutive fractional Zener model at large strain are presented. Both viscoelastic Zener models consist of a nonlinear elastic spring and a fractional Maxwell Element in parallel. The fractional Maxwell Element represents the viscoelastic behaviour of the formulation. Here, development of a new fractional viscoelastic material model under consideration of finite strain theory is presented. Additionally, the constitutive equations based on two different algorithmic approaches to capture the fractional time integration within this material model are derived. The consideration of fractional Elements enables the characterization of highly inelastic, time dependent materials with relatively few material parameters. For the fractional Element, a material parameter α determines the transition of the rheological Element’s behaviour between spring ( α = 0 ) and dashpot ( α = 1 ). Accuracy and efficiency of a classical (non-recursive) and a new recursive algorithm to handle the fractional Elements have been verified and validated by the comparison of several finite Element (FE) simulations to material test results. The simulations found on finite strains and an implicit time integration scheme. Finally, a FE moulding simulation, found the extended constitutive model for the explicit time integration scheme has been carried out to illustrate the performance for large scale simulations in comparison to a real forming process and found to be quite efficient.
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A continuum mechanical approach to model asphalt
International Journal of Pavement Engineering, 2014Co-Authors: Christoph Zopf, Mario A. Garcia, Michael KaliskeAbstract:The goal of this paper is to contribute to tire–pavement-interaction analyses from a structural mechanics point of view. The proposed asphalt material model is used to analyse the strain–stress dependencies of an asphalt pavement which is cyclically loaded by a truck tire. For the analysis of tire and pavement as well as its interaction, a finite Element approach is utilised. The development of the material model is based on triaxial material tests of cylindrical specimens. The asphalt material is characterised by elastic, viscous (rate-dependent) and plastic behaviour. In order to enable the use of the model also for large deformations within the pavement, it is developed for finite strains. The proposed approach consists of five rheological constitutive branches in parallel. A nonlinear elastic material model is used, which represents the elastic behaviour. The plastic effects are considered by an endochronic frictional Element. One Maxwell Element and two fractional Maxwell Elements represent the visco...
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An orthotropic viscoelastic material model for passive myocardium: theory and algorithmic treatment.
Computer methods in biomechanics and biomedical engineering, 2014Co-Authors: F. Barış Can Cansız, Hüsnü Dal, Michael KaliskeAbstract:This contribution presents a novel constitutive model in order to simulate an orthotropic rate-dependent behaviour of the passive myocardium at finite strains. The motivation for the consideration of orthotropic viscous effects in a constitutive level lies in the disagreement between theoretical predictions and experimentally observed results. In view of experimental observations, the material is deemed as nearly incompressible, hyperelastic, orthotropic and viscous. The viscoelastic response is formulated by means of a rheological model consisting of a spring coupled with a Maxwell Element in parallel. In this context, the isochoric free energy function is decomposed into elastic equilibrium and viscous non-equilibrium parts. The baseline elastic response is modelled by the orthotropic model of Holzapfel and Ogden [Holzapfel GA, Ogden RW. 2009. Constitutive modelling of passive myocardium: a structurally based framework for material characterization. Philos Trans Roy Soc A Math Phys Eng Sci. 367:3445–347...
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A constitutive model for finite deformation of amorphous polymers
International Journal of Mechanical Sciences, 2012Co-Authors: R. Fleischhauer, Michael Kaliske, Hüsnü Dal, K. SchneiderAbstract:The paper introduces a three-dimensional constitutive model for the mechanical behavior of amorphous polymers, thermosets and thermoplastics. The approach is formulated in terms of finite deformations, appropriate for glassy polymers. The rheology of the model consists of a Langevin-type free energy function for the energy storage due to molecular alignment connected in parallel to a Maxwell Element with a viscoplastic dashpot. The model proves successful for the constitutive description of glassy polymers over a large range of strain rates. To capture the smooth softening behavior upon yielding is the main purpose of this research. It is reached under consideration of absolute temperature and current strain rate with the proposed evolution law for the viscoplastic dashpot deformation. The rate-dependence of amorphous polymers is reproduced as well as the pressure dependence during different loading scenarios. A fully implicit numerical scheme appropriate for the finite Element implementation is presented. The modeling capability of the proposed approach is demonstrated for epoxy, PC and PMMA. The efficiency of the proposed numerical scheme is demonstrated via a necking simulation of a flat PC coupon.
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Formulation and implementation of three-dimensional viscoelasticity at small and finite strains
Computational Mechanics, 1997Co-Authors: Michael Kaliske, H. RothertAbstract:Purely elastic material models have a limited validity. Generally, a certain amount of energy absorbing behaviour can be observed experimentally for nearly any material. A large class of dissipative materials is described by a time- and frequency-dependent viscoelastic constitutive model. Typical representatives of this type are polymeric rubber materials. A linear viscoelastic approach at small and large strains is described in detail and this makes a very efficient numerical formulation possible. The underlying constitutive structure is the generalized Maxwell-Element. The derivation of the numerical model is given. It will be shown that the developed isotropic algorithmic material tensor is even valid for the current configuration in the case of large strains. Aspects of evaluating experimental investigations as well as parameter identification are considered. Finally, finite Element simulations of time-dependent deformations of rubber structures using mixed Elements are presented.