• Journal of Biosystems Engineering
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• v.14 no.3
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• pp.181-187
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• 1989

The mechanical and rheological properties of agricultural materials which influence the machine design or handling are not completely understood. Agricultural materials do not react in a purely elastic manner, and their responses when subjected to stress and strain appear a combination of elastic and viscous behavior. Many researchers have studied the mechanical and rheological properties of the various agricultural materials, but those properties are available mostly for foreign varieties of agricultural products. Rheological properties of rice seedlings become important to formulate the principles governing their mechanical behavior. The objectives of this study were to experimentally determine the creep and recovery behavior of rice seedlings of one japonica-type and one Indica x japonica hybrid in the transplanting age. The results of this study are summarized as follows; 1. The compression creep and recovery behavior of mat-type seedlings could be described by 4-element Burger's model. 2. The steady-state creep appeared at the stress larger than 0.8 MPa and the logarithmic creep appeared at the stress smaller than 0.8 MPa. 3. In the compression creep test of the rice seedlings, the instantaneous elastic modulus of Burger's model showed the range from 20 to 40 MPa. The higher value of absolute viscosity for the rice seedling explained that the rice seedlings were viscoelastic materials. 4. In the recovery test of the rice seedlings, there was a tendency that the higher permanent strain of all samples was observed under the smaller stress being appeared, and the larger permanent strain in Dongjin was observed than in Samkang.

• Korea-Australia Rheology Journal
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• v.14 no.2
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• pp.77-86
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• 2002

A microscopic theoretical study is performed to predict the rheological properties of human blood in the low concentration limit. The shear thinning behavior of blood in the low shear limit is studied by considering the aggregate formation of red blood cells, which is called the rouleaux formation. Then the constitutive equations of blood in the high shear limit are derived for various flow situations by considering the unique features of deformation of blood cells. Specifically, the effects of the surface-area-preserving constraint and the lank-treading motion of blood cells on the rheological properties are studied.

• Korea-Australia Rheology Journal
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• v.12 no.2
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• pp.101-105
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• 2000

The crystallization behavior of homo polypropylene (PP) and PP in the PP-poly($\varepsilon$-caprolactone) (PCL) blends during isothermal crystallization has been investigated using differential scanning calorimeter (DSC) and advanced rheometric expansion system (ARES). From the storage modulus data of the homo PP and PP-PCL blends during isothermal crystallization, the volume fraction of crystallized material ($X_t$) of the homo PP and PP in the PP-PCL blends was calculated using the various rheological models. The results of $X_t$ of the homo PP and PP in the PP-PCL blends from ARES measurement were compared with the results from DSC. The $X_t$ of the homo PP was found to be higher in the ARES measurement than in the DSC. The crystallization rate of the homo PP was found to be faster in the rheological measurements than in the thermal analysis. The $X_t$ of PP in the PP-PCL blends with various compositions was obtained from the thermal analysis and rheological measurements. The $X_t$ of PP in the PP-PCL blends obtained from the thermal analysis and rheological measurements are not consistent. This discrepancy of $X_t$ may be due to the morphological changes resulted from the different crystallization kinetics of PP in the PP-PCL blends.

• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.1-6
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• 2005

In aqueous alumina tape casting, the effects of altering the composition of the suspensions, the binders and the casting thickness were studied. The rheological behavior of the suspensions and the defects of the dried tapes were examined and the relationships between them are discussed. The changes in the defect regions reported in the previous paper were related with the rheological properties with variations of the binder, the composition and the casting thickness. The shear thinning factor increased with the organic content and the solid content (the decrease of water content). The apparent viscosity increased with the shear thinning factor. The relation between the shear thinning factor and the log apparent viscosity was similar for all binder types. In the relation between the defect free region and the rheological properties, the defect free region became narrower with increasing casting thickness. The defect free region is independent of binder type. Therefore, the thicker tape is more difficult to produce in aqueous alumina tape casting. Knowledge of the rheological properties of the suspensions could help Predict the defect type and the possibility of defect free dried tapes.

• Journal of Biosystems Engineering
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• v.35 no.6
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• pp.408-412
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• 2010

Rheological properties of cereals such as rye are great important for the design of die for extrusion and the development of models for extrusion process. Therefore, this study was carried out to analyze the rheological properties according to moisture content of rye flour and extrusion temperature. Rheological properties of rye flour were investigated by using a capillary rheometer for moisture content of three levels (30, 35, 40%) and extrusion temperature of three levels (120, 130, $140^{\circ}C$). Determination coefficients for the relationship between apparent shear stress ($\tau_{ap}$) and apparent shear velocity ($\gamma_{ap}$) were relatively high in the range of 0.973 ~ 0.997 under each extrusion condition. The values of consistency index (K) was decreased with increasing moisture content and extrusion temperature. However, the value of flow behavior index (n) presented the highest value at moisture content of 35%, but it was not affected by extrusion temperature.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.1 no.1
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• pp.53-68
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• 1981

Most clays under sustained load exhibit time-dependent deformation because of creep movement of soil particles and many investigators have attempted to relate their findings to the creep behavior of natural ground and to the long-term stability of slopes. Since the creep behavior of clays may assume a variety of forms depending on such factors as soil plasticity, activity and water content, it is difficult and complicated to analyse the creep behavior of clays. Rheological models composed of linear springs in combination with linear or nonlinear dashpots and sliders, are generally used for the mathematical description of the time-dependent behavior of soils. Most rheological models, however, have been proposed to simulate the behavior of secondary compression for saturated clays and few definitive data exist that can evaluate the behavior of non-saturated clays under the action of sustained stress. The clays change gradually from a solid state through plastic state to a liquid state with increasing water content, therefore, the rheological models also change. On the other hand, creep is time-dependent, and also the effect of thixotropy is time-function. Consequently, there may be certain correlations between creep behavior and the effects of thixotropy in compacted clays. In addition, the states of clay depend on water content and hence the height of the specimen under drained conditions. Futhermore, based on present and past studies, because immediate elastic deformation occurs instantly after the pressure increment without time-delayed behavior, the factor representing immediate elastic deformations in the rheological model is necessary. The investigation described in this paper, based on rheological model, is designed to identify the immediate elastic deformations and the effects of thixotropy and height of clay specimens with varing water content and stress level on creep deformations. For these purposes, the uniaxial drain-type creep tests were performed. Test results and data for three compacted clays have shown that a linear top spring is needed to account for immediate elastic deformations in the rheological model, and at lower water content below the visco-plastic limit, the effects of thixotropy and height of clay specimens can be represented by the proposed rheological model not considering the effects. Therefore, the rheological model does not necessitate the other factors representing these effects. On the other hand, at water content higher than the visco-plastic limit, although the state behavior of clays is visco-plastic or viscous flow at the beginning of the test, the state behavior, in the case of the lower height sample, does not represent the same behavior during the process of the test, because of rapid drainage. In these cases, the rheological model does not coincide with the model in the case of the higher specimens.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.137-140
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• 2005

Exfoliated nanocomposites of polypropylene/layered silicate were prepared by a melt compounding process using maleic anhydride modified polypropylene (PP-g-MAH) and organoclay. It was found that polypropylene/layered silicate nanocomposites exhibited remarkable reinforcement compared with the pure polypropylene or conventional composite filled with agglomerated organoclay. The polypropylene /layered silicate nanocomposites showed stronger and earlier shear thinning behaviors and outstanding strain hardening behavior than pure polypropylene or other conventional composites in shear and uniaxial elongational flows, respectively. We simulated rheological modeling for the pure polymer matrix and polypropylene/layered silicate nanocomposite in shear and elongational flows using K-BKZ integral constitutive equation. The two types of K-BKZequations have been examined to describe experimental results of shear and uniaxial elongational viscosities of pure polypropylene and polypropylene/layered silicate nanocomposite.

• Korea-Australia Rheology Journal
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• v.16 no.4
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• pp.201-212
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• 2004

Properties of polymer based nanocomposites depend on dispersion state of embedded fillers. In order to examine the effect of dispersion state on rheological properties, a new bi-mode FENE dumbbell model was proposed. The FENE dumbbell model includes two separate ensemble sets of dumbbells with different fric­tion coefficients, which simulate behavior of well dispersed and aggregated carbon nanotubes (CNTs). A new parameter indicating dispersion state of the CNT was proposed to account for degree of dispersion quantitatively as well as qualitatively. Rheological material functions in elongational, steady shear, and oscillatory shear flows were obtained numerically. The CNT/epoxy nanocomposites with different dis­persion state were prepared depending on whether a solvent is used for the dispersion of CNTs or not. Dis­persion state of the CNT in the epoxy nanocomposites was morphologically characterized by the field emission scanning electronic microscope and the transmission electron microscope images. It was found that the numerical prediction was in a good agreement with experimental results especially for steady state shear flow.

• Fibers and Polymers
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• v.6 no.4
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• pp.289-296
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• 2005

Biodegradable nanocomposites were prepared by mixing a polymer resin and layered silicates by the melt intercalation method. Internal structure of the nanocomposite was characterized by using the small angle X-ray scattering (SAXS) and transmission electron microscope (TEM). Nanocomposites having exfoliated and intercalated structures were obtained by employing two different organically modified nanoclays. Rheological properties in shear and extensional flows and biodegradability of nanocomposites were measured. In shear flow, shear thinning behavior and increased storage modulus were observed as the clay loading increased. In extensional flow, strain hardening behavior was observed in well dispersed system. Nanocomposites with the exfoliated structure had better biodegradability than nanocomposites with the intercalated structure or pure polymer.

• Journal of Powder Materials
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• v.17 no.1
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• pp.44-51
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• 2010

The rheological behavior of a cordierite honeycomb extrusion paste was investigated by measuring torque values in a Brabender plastograph. The extrusion pastes were formulated using binder (methy cellulose, MC), solvent (water), plasticizer (ploy ethylene glycol, PEG) and lubricants (oleic acid, OA). The mixing sequence and optimum organic binder, at least for homogeneous mixed state, can be determined from the rheological point of view. 3%MC-30%$H_2O$-1.5%PEG-1.0%OA with respect to the cordierite powder was chosen as a binder composition for the extrusion process of cordierite powder.