• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2252-2263
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• 1993

The purpose of this study is to verify the vibration and damping characteristics of elastic-viscoelastic-elastic structures, theoretically and experimentally. The forth-order differential equations of motion are derived for the transverse vibration of three-layered plates with viscoelastic core layer. The equations consider both transverse displacements of the constraining layer and the bare base plate as variable and account for the effect of the transverse normal strain and the shear strain of viscoelastic core layer on the vibration of the plates. Finite difference analysis of the equations and experimental measurements are performed on the three-layered plates of completely free boundary condition. Comparative investigations on the theory and the results of direct frequency analysis of NASTRAN are carried out on the same structures.

• Journal of the Korean Society of Food Science and Nutrition
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• v.32 no.7
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• pp.1046-1052
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• 2003

Viscoelastic behavior of oxidized starch gel, modified with sodium hypochlorite (NaOCl) and the adding effects of protein in oxidized starch gel was studied by dynamic viscoelastic measurement. The storage modulus(G′) of starch gel increased with the increase of starch concentration. They showed higher value when starch suspension was treated to 95$^{\circ}C$ rather than 85$^{\circ}C$. Consistency of starch gel was decreased over 1.0% active Cl/g starch when heated to 95$^{\circ}C$, which means that the swelling of starch granules increased with concentration of NaOCl and showed more sensitive against shear. As the extent of oxidation increased, starch granules were easily destroyed. Therefore, it is hard to separate between compartment of leached-out amylose and that of amylopectin, which means that the ability of gel formation was reduced. When oxidized starches were gelatinized in presence of soy protein and sodium caseinate, it was found that G′ decreased, and frequency dependence of G′ and G" increased with the increased degree of oxidation in starch. The reduce of starch-protein interaction was thought to be through the dissociation of the branched amylopectin, which playa leading role in protein interaction, with the oxidation of starch.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.978-981
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• 2005

The vibration analysis of damped sandwich beam is conducted using finite element method. The equation of motion presented by Mead and Markus is used to formulate FEM. Also as the thickness of the core in the damped sandwich beam goes to zero, conventional beam theory based on the transformed-section method and the equation of Mead and Markus are compared. According to the change of thickness and loss factor of the core, the forced frequency response of beam is calculated and discussed. And then using the half-power band width method, the damping ratio of each mode is calculated and discussed about each case.

• Korea-Australia Rheology Journal
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• v.19 no.1
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• pp.35-42
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• 2007

The effects of particle size distribution on the magnetorheological response of inverse ferrofluids was investigated using controlled mixtures of two monodisperse non-magnetisable powders of sizes $4.6\;{\mu}m\;and\;80{\mu}m$ at constant volume fraction of 30%, subjected to large amplitude oscillatory shear flow. In the linear viscoelastic regime (pre-yield region), it was found that the storage and loss moduli were dependent on the particle size as well as the proportion of small particles, with the highest storage modulus occurring for the monodisperse small particles. In the nonlinear regime (post yield region), Fourier analysis was used to compare the behaviour of the $1^{st}\;and\;3^{rd}$ harmonics ($I_{1}\;and\;I_{3}\;respectively$) as well as the fundamental phase angle as functions of the applied strain amplitude. The ratio of $I_{3}/I_{1}$ was found to become more pronounced with decreasing particle size as well as with increasing proportion of small particles in the bidisperse mixtures. Furthermore, the phase angle was able to clearly show the transition from solid-like to viscous behaviour. The results suggested that the nonlinear response of a bidisperse IFF is dependent on particle size as well as the proportion of small particles in the system.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.22 no.2
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• pp.167-173
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• 1996

The stability of gel structured emulsion and the effect of polyols on it have been studied by rheological property and interfacial tension. In this paper, three types of gel structured emulsions were prepared by using three polyols respectively(glycerine for sample 1, 1.3 BG for sample 2, PG for sample 3). And both complex modulus($G^*$) and loss angle[$\delta$ = tan-1(G"/G')] of samples were investigated against oscillating shear stress and frequency($\omega$). The results show sample 1 is most highly consistent with oscillating shear stress. And the results were compared with those of accelerated tests concerning storage stability of gel structured emulsion. To correlate consistency of rheological property with storage stability, interfacial tension from which adsorption efficiency of surfactant(Octyldodecyl Ether) could be known was measured. Sample 1 showed the largest value of [$d{\gamma}/dIn_{Cconc. of surfactant}$] in Gibbs equation. In summary, the prediction of stability could be correctly made by the consistency of rheological property(G*,$\gamma$) of gel structured emulsion against oscillating shear stress and it could be supported by measuring interfacial tension. And polyol affected the value of [$d{\gamma}/dIn_{Cconc. of surfactant}$], consequently affected the stability.lity.

• Geomechanics and Engineering
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• v.12 no.5
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• pp.849-862
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• 2017

With growing interests in using bacterial biopolymers in geotechnical practices, identifying mechanical properties of soft gel-like biopolymers is important in predicting their efficacy in soil modification and treatment. As one of the promising candidates, dextran was found to be produced by Leuconostoc mesenteroides. The model bacteria utilize sucrose as working material and synthesize both soluble and insoluble dextran which forms a complex and inhomogeneous polymer network. However, the traditional rheometer has a limitation to capture in situ properties of inherently porous and inhomogeneous biopolymers. Therefore, we used the particle tracking microrheology to characterize the material properties of the dextran polymer. TEM images revealed a range of pore size mostly less than $20{\mu}m$, showing large pores > $2{\mu}m$ and small pores within the solid matrix whose sizes are less than $1{\mu}m$. Microrheology data showed two distinct regimes in the bacterial dextran, purely viscous pore region of soluble dextran and viscoelastic region of the solid part of insoluble dextran matrix. Diffusive beads represented the soluble dextran dissolved in an aqueous phase, of which viscosity was three times higher than the growth medium viscosity. The local properties of the insoluble dextran were extracted from the results of the minimally moving beads embedded in the dextran matrix or trapped in small pores. At high frequency (${\omega}>0.2Hz$), the insoluble dextran showed the elastic behavior with the storage modulus of ~0.1 Pa. As frequency decreased, the insoluble dextran matrix exhibited the viscoelastic behavior with the decreasing storage modulus in the range of ${\sim}0.1-10^{-3}Pa$ and the increasing loss modulus in the range of ${\sim}10^{-4}-1\;Pa$. The obtained results provide a compilation of frequency-dependent rheological or viscoelastic properties of soft gel-like porous biopolymers at the particular conditions where soil bacteria produce bacterial biopolymers in subsurface.

• Macromolecular Research
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• v.8 no.1
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• pp.34-43
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• 2000

The melt rheology of four binary blends of ethylene 1-octene copolymers (EOCs) which consist of one component by Ziegler-Natta and another by metallocene catalysts, was studied to elucidate miscibility in the melt by using torsion rheometer at 200$\^{C}$ and different shear rates. The four blend systems, designated into the FA+FM, SF+FM, RF+EN, and RF+PL blend, are divided and interpreted based on the melt index (MI), the density and the comonomer contents. The melt viscosity such asη', η", and η$\^$*/ is weight average value if the comonomer contents are similar, otherwise they show different manner. The experimental resole are analyzed based on the Cole-Cole plot of logη' uersus log η", the logarithmic plots of the dynamic storage modulus (G') versus the dynamic loss modulus (G") for various blend compositions, and the melt viscosity of 11', n", and f" as a function of blend compositions. As a cerise-quence, the FA+FM blend is miscible, but the SF+FM, RF+EN, and RF+PL blends are not in the melt. Thus miscibility of the blends studied in this communication is suggested to strongly influence by the comonomer contents rather than the density or the MI.

• Preventive Nutrition and Food Science
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• v.19 no.4
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• pp.358-362
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• 2014

Flow and dynamic rheological properties of hot thickened soups for consumption by the elderly people with swallowing difficulty (dysphagia) were investigated at a serving temperature of $60^{\circ}C$. In this study, sea mustard soup (SMS) and dried pollock soup (DPS), which have been widely known as favorable hot soups provided in a domestic hospitals and nursing homes for dysphagic patients, were thickened with four commercial xanthan gum (XG)-based food thickeners (coded A~D) marketed in Korea. Thickened soups prepared with different thickeners showed high shear-thinning flow behaviors (n=0.15~0.21). Apparent viscosity (${\eta}_{a,50}$), consistency index (K), storage modulus (G'), and loss modulus (G") demonstrated differences in rheological behaviors between the XG-based thickeners. The magnitudes of (G') were much higher than those of (G") over the entire range of frequency (${\omega}$) with the high dependence on ${\omega}$, showing the rheological behavior similar to a weak gel. In general, all rheological parameter values of thickened DPS samples were higher when compared to the thickened SMS samples. These results indicate that flow and dynamic rheological properties of hot thickened soups containing commercial XG-based thickeners are strongly dependent on the type of thickener and soup.

• Polymer(Korea)
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• v.24 no.1
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• pp.38-47
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• 2000

A study of linear and branched polycarbonates blend system is presented. Flow and mechanical properties, and miscibility were studied for the blends of various compositions. No phase separations were observed in the blend systems. The mechanical properties of blends were examined through tensile strength, tensile modulus, flexural strength, flexural modulus and impact strength. Melt viscosity, storage and loss moduli of the blends with various compositions were examined at various temperatures. The dependence of viscosity on molecular weight was also presented. Flow properties of the blends showed significant variations however, mechanical properties were relatively independent of the compositions. As the content of branched polycarbonate increased, the dependence of viscosity on molecular weight and shear thinning behavior became more marked. Therefore the blend systems which have same mechanical properties but different flow properties can be obtained.

• Journal of Pharmaceutical Investigation
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• v.41 no.3
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• pp.161-171
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• 2011

The objective of the present study is to systematically characterize a linear viscoelastic behavior of petroleum jelly in small amplitude oscillatory shear flow fields correspondent to the rheological ground state. With this aim, using a strain-controlled rheometer, the dynamic viscoelastic properties of commercially available petroleum jelly have been measured at $37^{\circ}C$ (body temperature) over a wide range of angular frequencies at an extremely small strain amplitude of 0.1 %. In this article, the linear viscoelastic behavior was reported in detail and then explained from a structural view-point of petroleum jelly and discussed in depth with respect to the consumer's requirements. Main findings obtained from this study can be summarized as follows : (1) The storage modulus is always greater than the loss modulus over an entire range of angular frequencies studied, meaning that the linear viscoelastic behavior of petroleum jelly is dominated by an elastic nature rather than a viscous nature. (2) Petroleum jelly shows a desirable linear viscoelastic behavior with respect to the consumer's requirements because it is undesirable for the product to flow down from the skin at an initial stage upon contact with the human skin. (3) A fractional derivative model shows an excellent applicability to describe a linear viscoelastic behavior of petroleum jelly. However, this model should be used with a special caution because there exists no physical meaning for the model parameters. (4) A modified form of the Cox-Merz rule gives a good ability to predict the relationship between steady shear flow properties (nonlinear behavior) and dynamic viscoelastic properties (linear behavior) for petroleum jelly.