scholarly journals A visco-poroelastic theory for polymeric gels

2012 ◽  
Vol 468 (2148) ◽  
pp. 3824-3841 ◽  
Author(s):  
Xiao Wang ◽  
Wei Hong
Keyword(s):  
Chemical Potential ◽  
Polymer Network ◽  
Initial Boundary ◽  
Material Model ◽  
Viscoelastic Deformation ◽  
Simple Material ◽  
Transient Behaviour ◽  
Polymeric Gels ◽  
Low Viscosity ◽  
Cross Links

A polymeric gel can imbibe solvent and swell. Besides the dilatational mode of deformation, which involves long-range solvent migration, a gel may also undergo volume-conserved deformation. For a macroscopic gel with covalent cross-links, the volume-conserved deformation is usually much faster. However, these two modes are coupled for deformation at the microscopic level and for gels containing physical cross-links or large solvent molecules. In this paper, we seek to formulate a unified theoretical framework for the transient behaviour of polymeric gels to account for both solvent migration and viscoelastic deformation. Under this framework, we further develop a simple material model, and implement it into a finite-element code for numerical calculations. By simultaneously tracking the solvent migration and motion of polymer network, we evolve the inhomogeneous fields of stress and chemical potential. Several initial-boundary-value problems are solved as illustrative examples. For macroscopic gels with low viscosity, the time scales for viscoelasticity and poroelasticity are separated, and the long-term behaviour is just as that predicted by a poroelastic model. For structures or processes involving sizes comparable to the intrinsic length of a material, the viscoelasticity and poroelasticity must be considered simultaneously, especially when studying impact responses.

scholarly journals A Variational Approach and Finite Element Implementation for Swelling of Polymeric Hydrogels Under Geometric Constraints

2010 ◽  
Vol 77 (6) ◽  
Author(s):  
Min Kyoo Kang ◽  
Rui Huang
Keyword(s):  
Finite Element ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
Variational Approach ◽  
Chemical Potential ◽  
Polymer Network ◽  
Material Model ◽  
Geometric Constraints ◽  
Free Energy Function ◽  
Finite Element Implementation

A hydrogel consists of a cross-linked polymer network and solvent molecules. Depending on its chemical and mechanical environment, the polymer network may undergo enormous volume change. The present work develops a general formulation based on a variational approach, which leads to a set of governing equations coupling mechanical and chemical equilibrium conditions along with proper boundary conditions. A specific material model is employed in a finite element implementation, for which the nonlinear constitutive behavior is derived from a free energy function, with explicit formula for the true stress and tangent modulus at the current state of deformation and chemical potential. Such implementation enables numerical simulations of hydrogels swelling under various constraints. Several examples are presented, with both homogeneous and inhomogeneous swelling deformation. In particular, the effect of geometric constraint is emphasized for the inhomogeneous swelling of surface-attached hydrogel lines of rectangular cross sections, which depends on the width-to-height aspect ratio of the line. The present numerical simulations show that, beyond a critical aspect ratio, creaselike surface instability occurs upon swelling.

scholarly journals Are Single Polymer Network Hydrogels with Chemical and Physical Cross-Links a Promising Dynamic Vibration Absorber Material? A Simulation Model Inquiry

Materials ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5127
Author(s):  
Leif Kari
Keyword(s):  
Simulation Model ◽  
Loss Factor ◽  
Polymer Network ◽  
Vibration Absorber ◽  
Vibration System ◽  
Frequency Range ◽  
Dynamic Vibration Absorber ◽  
High Loss ◽  
Dynamic Vibration ◽  
Cross Links

Tough, doubly cross-linked, single polymer network hydrogels with both chemical and physical cross-links display a high loss factor of the shear modulus over a broad frequency range. Physically, the high loss factor is resulting from the intensive adhesion–deadhesion activities of the physical cross-links. A high loss factor is frequently required by the optimization processes for optimal performance of a primary vibration system while adopting a dynamic vibration absorber, in particular while selecting a larger dynamic vibration absorber mass in order to avoid an excess displacement amplitude of the dynamic vibration absorber springs. The novel idea in this paper is to apply this tough polymer hydrogel as a dynamic vibration absorber spring material. To this end, a simulation model is developed while including a suitable constitutive viscoelastic material model for doubly cross-linked, single polymer network polyvinyl alcohol hydrogels with both chemical and physical cross-links. It is shown that the studied dynamic vibration absorber significantly reduces the vibrations of the primary vibration system while displaying a smooth frequency dependence over a broad frequency range, thus showing a distinguished potential for the tough hydrogels to serve as a trial material in the dynamic vibration absorbers in addition to their normal usage in tissue engineering.

The nodular granite of Castanheira, north central Portugal: origin of the nodules and evidence for diapiric mobilization of granite

1993 ◽  
Vol 130 (2) ◽  
pp. 145-153 ◽  
Author(s):  
R. J. Reavy ◽  
D. H. W. Hutton ◽  
A. A. Finch
Keyword(s):  
Chemical Potential ◽  
Structural Data ◽  
Vapour Phase ◽  
Vapour Bubble ◽  
North Central ◽  
Host Granite ◽  
Low Viscosity ◽  
Granite Body ◽  
Central Portugal ◽  
Strong Depletion

AbstractThe Castanheira pluton in north-central Portugal is a small (1000 m × 600 m) granite body of Hercynian age which contains a remarkable abundance of granite-cored, biotite-rimmed nodules. The nodules are interpreted as representing original bubbles in the uppermost volatile-rich zone of a granitic pluton. Strong depletion in K and Rb in the host granite around the nodules suggests that the biotite is magmatic in origin. The nodules may have formed by reaction between chloroferrate(II) complexes in the vapour phase and silicate melt, possibly followed by condensation of the vapour phase to a small granitic core. Motion of the vapour bubble stabilized a gradient in chemical potential with respect to the host granite, giving rise to the nodules. Chemical, petrological and structural data suggest that the pluton was part of a larger granite body, which was forcefully emplaced during synchronous transcurrent shearing. The inferred presence of volatiles, in addition to the pervasive tourmalinization of the roof zone, suggest that the magma was halogen-rich; this may imply that the magma had low viscosity.

Impact damage assessment by using peridynamic theory

2012 ◽  
Vol 2 (4) ◽  
Author(s):  
Erkan Oterkus ◽  
Ibrahim Guven ◽  
Erdogan Madenci
Keyword(s):  
Residual Strength ◽  
Damage Assessment ◽  
Impact Damage ◽  
Material Model ◽  
Mixed Mode Fracture ◽  
Simple Material ◽  
Peridynamic Theory ◽  
Load Paths ◽  
Compression After Impact ◽  
Building Components

AbstractThis study presents an application of peridynamic theory for predicting residual strength of impact damaged building components by considering a reinforced panel subjected to multiple load paths. The validity of the approach is established first by simulating a controlled experiment resulting in mixed-mode fracture of concrete. The agreement between the PD prediction and the experimentally observed behavior is remarkable especially considering the simple material model used for the concrete. Subsequently, the PD simulation concerns damage assessment and residual strength of a reinforced panel under compression after impact due to a rigid penetrator.

DO WE NEED VERY STIFF FILLERS?

2017 ◽  
Vol 90 (4) ◽  
pp. 743-750 ◽  
Author(s):  
Bing Jiang
Keyword(s):  
Material Model ◽  
Chain Scission ◽  
Rubber Matrix ◽  
Macroscopic Strain ◽  
Stress Strain ◽  
Simple Material ◽  
Strain Concentration ◽  
Trade Offs ◽  
Reinforcing Fillers ◽  
Balance Trade

ABSTRACT The influence of reinforcing fillers on the stretching of a rubber matrix is analyzed. It is shown that a filler stiffness higher than a critical stiffness does not further enhance the stiffness of the reinforced elastomer. The stiffer filler induces a higher stress–strain concentration and causes filler–rubber dissociation or chain scission at a lower macroscopic strain. Reducing filler stiffness can reduce the stress–strain concentration and therefore delay rubber chain scission or dissociation from the filler surface. Accordingly, the toughness of the reinforced elastomer could be improved. A simple material model is developed to predict the maximum macroscopic strain without bond scission in a reinforced elastomer. It is shown that reduced filler stiffness is beneficial for cases with (i) reduced bond strength, (ii) increased rubber matrix stiffness, and (iii) increased application strain of the reinforced elastomer. The model can be used to design the appropriate filler stiffness to balance trade-offs of stiffness and toughness of reinforced elastomers.

Atomic Understanding of the Swelling and Phase Transition of Polyacrylamide Hydrogel

2016 ◽  
Vol 08 (07) ◽  
pp. 1640002 ◽  
Author(s):  
Shuai Xu ◽  
Ying Wang ◽  
Jianying Hu ◽  
Zishun Liu
Keyword(s):  
Phase Transition ◽  
Continuum Mechanics ◽  
Chemical Potential ◽  
Polymer Network ◽  
Point Of View ◽  
Dynamics Simulation ◽  
Mechanics Model ◽  
Basic Parameters ◽  
Solvent Molecules ◽  
And Diffusion

A polymer network can imbibe copious amounts of solvent (water) and swell, and the resulting state is known as a hydrogel. In this study, we have made the modification for the all-atom consistent valence force field (CVFF) to investigate the swelling property of polyacrylamide (PAM) hydrogel by molecular dynamics simulation. We have built 21 hydrogel models with different solvent contents and calculate the average chemical potential and diffusion coefficient of solvent molecules in PAM hydrogel. We find that when the mass fraction of solvent is about 90%, PAM hydrogel reaches its free swelling limitation and loses the motivation of absorbing solvent. Furthermore, it is also found that PAM hydrogel has a phase transition phenomenon when the values of solvent chemical potential are between [Formula: see text][Formula: see text]kcal/mol and [Formula: see text][Formula: see text]kcal/mol. This study will provide insight into the basic parameters which are widely used in continuum mechanics analysis of hydrogels from atomic point of view and help researchers to improve the continuum mechanics model for neutral hydrogel.

Comparison of Three Methods for Material Hardening Parameter Identification under Cyclic Tension-Compression Loadings: Roll Levelling Case Study

2015 ◽  
Vol 651-653 ◽  
pp. 957-962 ◽  
Author(s):  
Elena Silvestre ◽  
Eneko Sáenz de Argandoña ◽  
Lander Galdos ◽  
Joseba Mendiguren
Keyword(s):  
Parameter Identification ◽  
Kinematic Hardening ◽  
High Strength Steels ◽  
High Strength ◽  
Material Model ◽  
Forming Process ◽  
Element Analysis ◽  
Transient Behaviour ◽  
Cyclic Tension ◽  
Hardening Parameter

The roll levelling is a forming process used to remove the residual stresses and imperfections of metal strips by means of plastic deformations. The process is especially important to avoid final geometrical errors when coils are cold formed or when thick plates are cut by laser. In the last years, and due to the appearance of high strength materials such as Ultra High Strength Steels, machine design engineers are demanding a reliable tool for the dimensioning of the levelling facilities. In response to this demand, Finite Element Analysis is becoming an important technique able to lead engineers towards facilities optimization through a deeper understanding of the process.In this scenario, the accuracy and quality of the simulation results are highly dependent on the accuracy of the implemented material model. During roll levelling process, the sheet metal is subjected to cyclic tensile-compressive deformations, therefore a proper constitutive. model which considers the phenomena that occurs during cyclic loadings, such as the Bauschinger effec, work hardeningt and the transient behaviour, is needed. The prediction of all these phenomena which affect the final shape of the product are linked to the hardening rule.In the present paper, the roll levelling simulation of a DP1000 steel is performed using a combined isotropic-kinematic hardening formulation introduced by Chaboche and Lemaitre since its simplicity and its ability to predict the Bauschinger effect. The model has been fitted to the experimental curves obtained from a cyclic tension-compression test, which has been performed by means of a special tool developed to avoid the buckling of the specimen during compressive loadings. The model has been fitted using three different material hardening parameter identification methodologies which have been compared.

Elastically Effective Strand Density in Polymer Networks

1969 ◽  
Vol 42 (5) ◽  
pp. 1285-1293
Author(s):  
N. R. Langley
Keyword(s):  
Molecular Weight ◽  
Statistical Approach ◽  
Main Chain ◽  
Polymer Network ◽  
Polymer Networks ◽  
Entanglement Density ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Cross Links ◽  
New Criterion

Abstract A new expression is derived which relates the density of elastically effective strands in a polymer network to the densities of random cross-links, main-chain scissions, and entanglements and to the molecular weight distribution of the initial linear polymer. Methods are recommended for characterizing the cross-link and scission densities from measurable sol fractions and for determining the entanglement density empirically. The strand density can be evaluated quite easily for the random and uniform initial molecular weight distributions. The new expression differs appreciably from that of Mullins and Bueche, owing principally to a new criterion for effectively trapping network entanglements. The statistical approach used to derive the strand density is also used in a new derivation of an existing implicit expression for the gel fraction.

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