• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.7-20
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• 2017

In this study, effects of grain size distribution on the shear strength and rheological properties are investigated for coarse- and fine-grained soils by using direct shear apparatus. Shear strengths are estimated for fine-grained soils with the maximum particle size of 0.075 mm and coarse-grained soils with the maximum particle size of 0.425 mm and fine contents of 17% prepared at dry and liquid limit states. The direct shear tests are conducted under the relatively slow shear velocity, which corresponds to the reactivated landslide or debris flow after collapse according to the landslide classification. In addition, for the evaluation of rheological properties, residual shear strengths for both fine- and coarsegrained soils prepared under liquid limit states are obtained by multiple reversal shear tests under three shear velocities. From the relationship between residual shear strengths and shear rates, Bingham plastic viscosity and yield stress are estimated. The direct shear tests show that cohesions of fine-grained soil are greater than those of coarse-grained soil at both dry and liquid limit states. However, internal friction angles of fine-grained soil are smaller than those of coarse-grained soil. In case of rheological parameters, the plastic viscosity and yield stress of fine-grained soils are greater than those of coarse-grained soils. This study may be effectively used for the prediction of the reactivated landslide or debris flow after collapse.

• Journal of Microbiology and Biotechnology
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• v.1 no.1
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• pp.70-74
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• 1991

The rheological properties of rifamycin B fermentation broth using Nocardia mediterranei were characterized in concomitance with the chemical changes of the fermentation broth. The data were interpreted with various rheological models. As results, it was found that the rheological behaviour at the early growth phases of the culture was the Newtonian fluid, but it was changed to the non-Newtonian fluid (Casson plastic behaviour) at the later phases of the culture. Rheological parameters viz., apparent viscosity ($\mu_a$), yield shear stress ($\tau_o$), and Casson constant ($K_c$) were changed through the fermentation where cell concentrations were changed and mycelia were greatly branched. Those results indicated that cell concentration and cell morphology played important roles to determine the rheological characters.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1298-1302
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• 2000

Electrorheological(HER) and magnetorheologica(MR) fluids have a unique ability to increase the dynamic yield stress of the fluid substantially when electric or magnetic field is applied. ER and MR fluid-based dampers are typically analyzed using Bingham-plastic shear flow analysis under Quasi-steady fully developed flow conditions. An alternative perspective, supported by measurements reported in the literature, is to allow for post-yield shear thinning and shear thickening. To model these, the constant post-yield plastic viscosity in Bingham model can be replaced with a power-law model dependent on shear strain rate that is known as the Herschel-Bulkley fluid model. The objective of this paper is to predict the damping forces analytically in a typical ER bypass damper for variable electric field, or yield stress using Herschel-Bulkley analysis.

• Journal of the Korean Society of Safety
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• v.13 no.1
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• pp.85-91
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• 1998

Sol-gel derived silica films were prepared by dip-coating onto polymethylmethacylate with Tetraethoxysilane(TEOS) as starting materials. Film properties such as viscosity and thickness were investigated as a function of dip speed, waterprecursor ratio, sol aging time. IR spectra of the gel films prepared from TEOS at various R are given. At small values of R the absorption peaks assignable to C-H vibration in $-OC_2H_5$ groups are observed around 3000 and 1500-1300 $cm^{-1}$. These bands indicate that the -$-OC_2H_5$ groups are retained in the gel at small values of R because of incomplete hydrolysis of TEOS. Film behaviour was interpreted in terms of the dependence of hydrolysis and condensation rates on the interplay between sol pH and waterprecursor ratio. Film thickness was found to increase by approximately a factor of two as waterprecursor ratio increased from two to six. Film thickness also increased with sol prepolymerization time. Surface quality was correlated with processing conditions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.39-42
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• 2005

For mass production, usually injection mold has multi-cavity which is filled through geometrical balanced runner system. Despite geometrical balanced runner system, filling imbalances between cavity to cavity have always been observed. These filling imbalances are one of the most significant factors to affect quality of plastic parts when molding plastic parts in multi-cavity injection mold. Filling imbalances are results from non-symmetrical shear rate distribution within melt as it flows through the runner system. It has been possible to decrease filling imbalance by optimizing processing conditions, but it has not completely eliminated this phenomenon during injection molding processing. This paper presents a solution of these filling imbalances through using 'runner core pin'. The runner core pin which is developed in this study creates a symmetrical shear distribution within runner. As a result of using runner core pin, a remarkable improvement in reducing filling imbalance was confirmed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.09a
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• pp.13-16
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• 2005

For mass production, usually injection mold has multi-cavity which is filled through geometrical balanced runner system. Despite geometrical balanced runner system, filling imbalances between cavity to cavity have always been observed. These filing imbalances are one of the most significant factors to affect quality of plastic parts when molding plastic parts in multi-cavity injection mold. Filling imbalances are results from non-symmetrical shear rate distribution within melt as it flows through the runner system. It has been possible to decrease filling imbalance by optimizing processing conditions, but it has not completely eliminated this phenomenon during injection molding processing. This paper presents a solution of these filling imbalances through using 'runner core pin'. The runner core pin which is developed in this study creates a symmetrical shear distribution within runner. As a result of using runner core pin, a remarkable improvement in reducing filling imbalance was confirmed.

• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.637-644
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• 2001

A regularization method based on the Duvaut-Lions viscoplastic scheme for plastic-damage and continuum damage models, which provides mesh-independent and well-posed solutions in nonlinear earthquake analysis of concrete dams, is presented. A plastic-damage model regularized using the proposed rate-dependent viscosity method and its original rate-independent version are used for the earthquake damage analysis of a concrete dam to analyze the effect of the regualarization and mesh. The computational analysis shows that the regularized plastic-damage model gives well-posed solutions regardless mesh size and arrangement, while the rate-independent counterpart produces mesh-dependent ill-posed results.

• Design & Manufacturing
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• v.17 no.3
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• pp.28-33
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• 2023

The conventional FRP (Fiber Reinforced Plastic) manufacturing process used thermoset resins for ease of molding but faced the issue of non-recyclability. To address these shortcomings, a new process utilizing thermal plastic resin was developed. However, due to the high viscosity of thermal plastic resin, problems such as fiber deformation and a reduced fiber volume fraction occurred during the high-temperature, high-pressure process. In this study, to overcome the limitations of the conventional process, fiber-reinforced composite materials were manufactured through in-situ polymerization using PLA (Poly L-Lactide) resin in the VA-RTM (Vacuum Assistance Resin Transfer Molding) process. The fiber volume of the produced specimens was calculated, and resin impregnation and porosity were confirmed through optical microscopy. Additionally, molecular weight analysis using GPC (Gel Permission Chromatography) demonstrated improvements over the conventional process and emphasized the essential requirement of temperature control.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.103-111
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• 2011

This study examined rheological properties of blast furnace slag and ash paste that are widely used as cement concrete for mineral admixture in current. In that way rheological properties of the paste of mineral admixture only was examined. The result of this study were as follow: In order to analyze that the rheological properties of the mineral admixture only, fine particles were produced with grinding machine to 3 particle sizes. These powders in general from the result of comparison with and analysis of rheological properties and the coefficient n and De values. The result that ash powder was higher in plastic viscosity and yield stress than Slag powder, and with the same n value, ash powder showed higher plastic viscosity and yield stress than Slag powder. But Slag powder in particle size distribution showed a sensitive tendency on changing in rheological properties.

• Journal of the Korean Society of Safety
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• v.33 no.2
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• pp.86-93
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• 2018

Recently, the use of composite steel plate concrete structural modules filled with concrete between steel plates of complex internal structure, in which a large amount of studs are installed, is increasing in order to reduce the weight and to increase workability of structures such as LNG storage tanks. However, in Korea, there is no systematic criterion for evaluating the construction performance of composite steel plate concrete structural modules. Therefore, in this study, we propose a filling guideline of concrete for composite steel plate structural module. For this purpose, high filling performance concrete with general strength range was formulated and tested for filling ability and permeability for each formulation. Rheology analysis was performed to quantitatively evaluate the flow characteristics of concrete. The reliability of $T_{500}$ and plastic viscosity was evaluated to reflect the results of each test, and a guideline for high filling concrete satisfying the reliability of 0.9 or more was derived by reflecting the results of the study on the relationship between the $T_{500}$ and plastic viscosity. Through final fill-box test, filling performance was verified and guidelines were suggested.