Papers by Keyword: Viscoelastic Behavior

Abstract: The aim of this study was to improve the stability and rheological properties of water-in-oil-in-water (W/O/W) multiple emulsions containing 30 wt% paraffin oil, and 4 wt% polyglycerol-3-polycinoleate (PGPR) as a lipophilic surfactant. This was done by adding different concentrations of xanthan gum (GX) and the hydrophilic surfactants (Polyoxyethylene (80) sorbitan monooleate (Tween® 80), poloxamer 407(Lutrol® F127) using the emulsification in a two-steps process. The stability of the W/O/W multiple emulsions was analyzed over one-month storage period using physicochemical and rheological measurements. An excellent structure appeared with 0.175 wt% of xanthan gum in the outer aqueous phase and 1 wt% of Tween® 80. The modified Cross model was successfully applied to fit the flow curves of multiple W/O/W emulsions at different concentrations of xanthan gum. The incorporation of xanthan gum in a concentration range of 0.05-0.175 wt% induced an increase in the yield stress, in the zero-shear rate viscosity, and in the infinite shear rate viscosity of the multiple emulsions. The study also showed that adding xanthan gum in a concentration range of 0.05-0.175 wt% to W/O/W emulsions caused an increase in the viscosity of the system in the Newtonian regime and viscoelastic behavior.

Abstract: Oscillation and creep experiments have been performed with Semi-Solid Material (SSM) AlSi7 with 35% solid fraction to investigate the early visco-elastic properties after shearing of the material in a Searle Rheometer. The preparation of the SSM has been done in situ using a standard procedure to guarantee for all experiments the same initial properties of the material. First, oscillation experiments at low amplitude allowed to study the evolution of material structure with time. Subsequently, creep experiments have been performed changing the resting period based on previous results. Creep experiments are characterized by exposing the material to a sudden increase of shear stress. The resolution in time has been 0.01 seconds, which allows observing the dynamics of the development of visco-elastic properties.The material exhibits viscoelastic properties that are becoming more pronounced with longer resting time. This is in accordance with previous experiments where the ratio between elastic and viscous properties increases with increasing resting time. The development of the elastic properties follows the increase of the yield stress due to the creation of an internal structure of the material, which starts immediately after stopping shearing. The investigation of the short-term response of SSM can be particularly relevant for industrial practice, where material deformation during die filling is very fast and the material flow does not take place in steady-state condition.

Abstract: The present work is concerned with analysis of the dissipated energy in viscoelastic multilayered inhomogeneous beam structure. The layers of the beam are continuously inhomogeneous along the thickness. The Maxwell mechanical model is used for treating the viscoelastic behaviour of the beam. The moduli of elasticity and the coefficients of viscosity vary continuously along the thickness of each layer. The dissipated energy is obtained by integrating of the unit dissipated energy in the volume of the beam. A parametric investigation of the dissipated energy is carried-out by applying the solution derived in order to evaluate the influence of various factors.

Abstract: Pore-throat ratio is a significant parameter expressing the characteristics of reservoir pores. It has an apparent influence on viscoelastic polymer solution flow in micro-pores. In this paper, Upper-Convected Maxwell (UCM) equation is applied in describing the viscoelastic polymer behavior. The expansion channel models of different pore-throat ratio are selected in process of simulation. And contours of stream function and velocity of different Weissenberg number (We) are calculated and drawn by Finite Volume Method. Results show that, vortex will occur at the re-entrant corner caused by the sudden expansion of channel, size and intensity of the corner recirculation vortex. The residual oil region is reduced and the mobile oil region is enlarged. Microscopic sweep efficiency is increased relatively. Vortex will be larger and stronger, and the velocity will be increased for We. Vortex will be lager as the bigger pore-throat ratio. Micro-sweep efficiency will be capitalized by viscoelastic polymer solution to the utmost.

Abstract: Pore-throat ratio is a significant parameter expressing the characteristics of reservoir pores. It has an apparent influence on viscoelastic polymer solution flow in micro-pores. In this article, Upper-Convected Maxwell (UCM) equation is adapted to describe the viscoelastic polymer behavior. The contraction channel models of different pore-throat ratio are selected in process of simulation. And contours of stream function and velocity of different Weissenberg number (We) are calculated and drawn by Finite Volume Method. Results show that, vortex will occur at the re-entrant corner caused by the sudden contraction of channel, size and intensity of the corner recirculation vortex. The residual oil region is reduced and the mobile oil region is enlarged. Microscopic sweep efficiency is increased relatively. Vortex will be larger and stronger, and the velocity will be increased for We. Vortex will be lager with the bigger pore-throat ratio. Micro-sweep efficiency will be capitalized by viscoelastic polymer solution to the utmost.

Abstract: Natural rubber (polymer designation cis-1-4 polyisoprene, is obtained from the sap ("latex") of several rubber-yielding plants (e.g., HeveaBrasiliensis and Partheniaargentatum) by coagulation with chemicals, drying, electrical coagulation, and other processes. Foamy or sponge structure of natural rubber (NR) is very useful in aerospace and as auxetic materials (exhibiting negative poisons ratio) for use in application of homeland security.The main aim of this research to estimate the influence of carbon black on mechanical properties, curing and viscosity variation behaviors of the natural rubber based composites. Different amounts of carbon black were used along with other fillers. The influence of carbon black on curing behavior and mechanicalproperties of natural rubber foams was investigated at different feedingratios of the carbon black. The physical properties of the foamed NRs were then measured as a function of carbon blacks content. The mechanical properties of the foamed NRs such as tensile strength,strength at break and modulus,were gradually increased with increasingcarbon black content whereas elongation decreasedat break.

Abstract: In this work, a boundary element formulation for 2D linear viscoelastic solid polymers subjected to body force of gravity has been presented. Structural analysis of solid polymers is one of the most important subjects in advanced engineering structures. From basic assumptions of the viscoelastic constitutive equations and the weighted residual techniques, a simple but effective boundary element formulation is implemented for standard linear solid (SLS) model. The SLS model provides an approximate representation of observed behavior of a real advanced polymer in its viscoelastic range. This approach avoids the use of relaxation functions and mathematical transformations, and it is able to solve quasistatic viscoelastic problems with any load time-dependence and boundary conditions. Problem of pressurization of thick-walled viscoelastic tanks made of PMMA polymer, which subjected to a body force, is completely analyzed.

Abstract: In this paper, a 2D boundary element approach able to model viscoelastic functionally graded materials (FGM) is presented. A numerical implementation of the Somigliana identity for displacements is developed to solve 2D problems of exponentially graded elasticity. An FGM is an advanced material in which its composition changes gradually resulting in a corresponding change in properties of the material. The FGM concept can be applied to various materials for structural and functional uses. Our model needs only the Green’s function of nonhomogeneous elastostatic problems with material properties that vary continuously along a given dimension. We consider the material properties to be an exponential function of Cartesian coordinates x. As application, a numerical example is provided to validate the proposed boundary integral equation approach.

Abstract: We choose petroleum ether and n-heptane as poor solvent and selective solvent to swell styrene-butadiene-styrene (SBS) and prepare a kind of swelling SBS sample with different swelling degrees. The steady rate sweep tests have been carried out and the steady zero shear viscosities have been obtained for two kinds of equilibrium swelling SBS. Furthermore, the dynamic frequency sweep tests have been performed for swelling SBS with different swelling degrees. The test results show that the curves of dynamic storage modulus (G’) is always located over those of dynamic loss modulus (G”), which exhibits that the viscoelastic behaviors of all the samples is charged by elasticity in the whole frequency range measured. The poor solvent give less destroy to the network structure of SBS than the selective solvent.

Abstract: For high temperature applications of laminated composite structures, viscoelastic behavior of laminated composite structures is investigated by multi-scale analysis based on a homogenization theory. Effective viscoelastic properties of the laminas are evaluated by a boundary integral method at a micro-scale level, and viscoelastic analysis for laminated composite structures is performed by a finite element method at a macro-scale level using the effective viscoelastic properties of lamina obtained by the micro-scale analysis. In the multi-scale analysis, the Laplace transformation is adopted and the correspondence principle between elastic and viscoelastic solutions in the Laplace domain is applied. The inverse Laplace transform is formulated by the Duhamel integral, and is calculated numerically. As a numerical example, a laminated composite plate with a hole is treated and the viscoelastic behavior of the laminated composite structure is elucidated.