• Composites Research
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• v.34 no.3
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• pp.155-160
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• 2021

Metamaterials are complexes of elements that can create properties not found in naturally occurring materials, such as changing the direction of forces, creating negative stiffness, or altering vibration and impact properties. In the case of wood pile metamaterials that are easy to manufacture and have excellent performance in reducing vibration and shock in the vertical direction, basic research on variables affecting shock transmission is needed to reduce shock. Although research on impact reduction according to geometrical factors is being conducted recently, studies on the effect of material variables on impact reduction are insufficient. In this paper, finite element analysis was carried out by variablizing the geometrical properties (lamination angle, diameter, length) and material properties (modulus of elasticity, specific gravity, Poisson's ratio) of wood pile cylinders. Through finite element analysis, the shape of the wooden pile cylinder delivering impact was confirmed, and the effect of each variable on the reduction of impact force and energy was considered through main effect diagram analysis, and frequency band analysis was performed through fast Fourier transform. proceeded In order to reduce the impact force and vibration, it was found that the variables affecting the contact area of t he cylinder have a significant effect.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.173-181
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• 2021

Reinforced concrete structures are exposed to various environments, resulting in reinforcement corrosion due to moisture and ions penetration. Reinforced concrete corrosion causes a decrease in the durability performance of reinforced concrete structures. One solution to mitigate such issues is using FRP rebars, which offer several advantages such as high tensile strength, corrosion resistance, and light-weight than conventional rebars, in reinforced concrete instead of conventional steel rebars. The FRP rebar used should be examined at the limit state because FRP reinforced concrete has linear behavior until its fracture and can generate excessive deflection due to the low elastic modulus. It should be considered while designing FRP reinforced concrete for flexure. In the ultimate limit state, the flexural strength of FRP reinforced concrete as per ACI 440.1R is significantly lower than the flexural strength by applying both the environmental reduction and strength reduction factors accounting for the material uncertainty of FRP rebar. Therefore, in this study, the experimental results were compared with the deflection of the proposed effective moment of inertia referring to the local and international standards. The experimental results of GFRP and BFRP reinforced concrete were compared with the flexural strength as determined by ACI 440.1R and Fib bulletin 40. The flexural strength obtained by the experimental results was more similar to that obtained by Fib bulletin 40 than ACI 440.1R. The flexural strength of ACI 440.1R was conservatively evaluated in the tension-controlled section.

• Composites Research
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• v.35 no.2
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• pp.115-119
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• 2022

The performance of carbon fiber is important for the production of these high-quality polymer composite materials such as CFRP (Carbon Fiber Reinforced Plastic). For this purpose, it is essential to use an optimized spinning process for improving the mechanical, physical, and structural properties of the precursor fiber, which greatly affects the properties of the carbon fiber, and the use of a suitable precursor polymer. In this study, the content of MAA (Methacrylic Acid), MAA injection time, and concentration of AIBN (2,2'-Azobis(2-methylpropionitrile)) were set as parameters for the polymer synthesis process, and Poly(AN-co-MAA) (poly(acrylonitrile-co-methacrylic acid)) was polymerized by solution polymerization. Poly(AN-co-MAA) with a molecular weight of 305,138 g/mol and an MAA ratio of 4.2% was dissolved in DMF (N,N-dimethylformamide) at a concentration of 16.0 wt%, and then a precursor fiber was prepared through dry-jet-wet spinning. The precursor fiber had a tensile strength of ~1.06 GPa and a tensile modulus of ~22.01 GPa, and no voids and structural defects were observed on the fiber.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.47-54
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• 2006

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomena are negligible. However, the terms of effective stresses are divided into the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by ${\alpha}$ parameters and ${\beta}$ exponents that are experimentally determined. The ${\beta}$ exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the ${\alpha}$ parameters are changed by contact behaviors among particles, material properties of particles, and type of packing (i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies by using bender elements. Results show the shear wave velocity depends on the stress-induced anisotropy for round particles. Furthermore, the shear wave velocity is dependent on particle alignment under the constant evvective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully estimated and used for the design and construction of geotechnical structures.

• Steel and Composite Structures
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• v.47 no.1
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• pp.91-102
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• 2023

To study the evaluation standard and control limit of mortar filling layer void length, in this paper, the train sub-model was developed by MATLAB and the track-bridge sub-model considering the mortar filling layer void was established by ANSYS. The two sub-models were assembled into a train-track-bridge coupling dynamic model through the wheel-rail contact relationship, and the validity was corroborated by the coupling dynamic model with the literature model. Considering the randomness of fastening stiffness, mortar elastic modulus, length of mortar filling layer void, and pier settlement, the test points were designed by the Box-Behnken method based on Design-Expert software. The coupled dynamic model was calculated, and the support vector regression (SVR) nonlinear mapping model of the wheel-rail system was established. The learning, prediction, and verification were carried out. Finally, the reliable probability of the amplification coefficient distribution of the response index of the train and structure in different ranges was obtained based on the SVR nonlinear mapping model and Latin hypercube sampling method. The limit of the length of the mortar filling layer void was, thus, obtained. The results show that the SVR nonlinear mapping model developed in this paper has a high fitting accuracy of 0.993, and the computational efficiency is significantly improved by 99.86%. It can be used to calculate the dynamic response of the wheel-rail system. The length of the mortar filling layer void significantly affects the wheel-rail vertical force, wheel weight load reduction ratio, rail vertical displacement, and track plate vertical displacement. The dynamic response of the track structure has a more significant effect on the limit value of the length of the mortar filling layer void than the dynamic response of the vehicle, and the rail vertical displacement is the most obvious. At 250 km/h - 350 km/h train running speed, the limit values of grade I, II, and III of the lengths of the mortar filling layer void are 3.932 m, 4.337 m, and 4.766 m, respectively. The results can provide some reference for the long-term service performance reliability of the ballastless track-bridge system of HRS.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.109-125
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• 2023

Disposal repository for high-level radioactive waste secures its safety by means of engineered and natural barriers. The performance of these barriers should be tested and verified through various aspects in terms of short and/or long-term. KAERI has been conducting various in-situ demonstrations in KURT (KAERI Underground Research Tunnel). After completing previous experiment, a conceptual design of an improved in-situ experiment, i.e. K-COIN (KURT experiment of THMC COupled and INteraction), was established and detailed planning for the experiment is underway. Preliminary characterizations were conducted in KURT for siting a K-COIN test site. 15 boreholes with a depth of about 20 m were drilled in three research galleries in KURT and intact rock specimens were prepared for laboratory tests. Using the specimens, physical measurements, uniaxial compression, indirect tension, and triaxial compression tests were conducted. As a result, specific gravity, porosity, elastic wave velocities, uniaxial compressive strength, Young's modulus, Poisson's ratio, Brazilian tensile strength, cohesion, and internal friction angle were estimated. Statistical analyses revealed that there did not exist meaningful differences in intact rock properties according to the drilled sites and the depth. Judging from the uniaxial compressive strength, which is one of the most important properties, all the specimens were classified as very strong rock so that mechanical safety was secured in all the regions.

• Elastomers and Composites
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• v.37 no.4
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• pp.244-257
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• 2002

A thermotropic liquid crystalline polymer(TLCP) which has flexible butylene/hexylene spacers in the main chain and a triad aromatic ester type mesogenic unit containing a naphthyl group was prepared by solution polycondensation. The in-situ composites based on poly(ethylene 2,6-naphthalate) (PEN) and a thermotropic liquid crystalline polymer(TLCP) were prepared and melt spun at different TLCP contents and different draw ratios to produce monofilaments. Blends of the TLCP with PEN were investigated in terms of thermal, mechanical properties and morphology. The TLCP synthesized showed nematic mesophasic behavior and its transition temperature to isotropic melt from mesophase was 249℃. The blends showed well dispersed TLCP phases in the PEN matrix without macroscopic phase separation. Inclusion of TLCP in the blends decreased the cold crystallization temperature of PEN in the blend, therefore, the TLCP acts as a nucleating agent in the blend and showed good interfacial adhesion between the dispersed LCP phases and PEN matrix with domain sizes 40~50 nm in diameter and well developed fibrillation in the monofilaments. The TLCP acted effectively as a reinforcing material in the PEN matrix at the 10wt% level, it led to an increase of initial modulus up to 270% and tensile strength by 235%, while the elongation rate increasing with higher draw ratios.

• Economic and Environmental Geology
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• v.57 no.2
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• pp.185-204
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• 2024

This study was conducted for evaluation the geological, physical, and chemical properties of domestic sand by analyzing about 4,800 quality data of natural sand from river and land area surveyed until 2023 through the aggregate resource survey conducted by the Ministry of Land, Infrastructure and Transport. The average depth of the Quaternary unconsolidated sedimentary layer in Korea, which includes a sand layer, is about 10m (maximum depth 66m). The thickness of the sand layer within the sedimentary layer is most dominant in the range of 0.5m to 4.0m. This accounts for about 70% of the entire sand layer. In the sand layer, the ratio of sand, gravel, and clay is 60:20:10. Regardless of the provenance or geology, the sand is mainly composed of quartz, plagioclase, and K-feldspar, and the minor minerals are muscovite, biotite, chlorite, magnetite, epidote. The sand includes in 45~75% of quartz, 5~20% of plagioclase and K-feldspar, each other. And other minor minerals are included in 10%. The average grain size of sand is 0.5mm to 1.0mm, which accounts for 44% of sand samples. The water absorption rate and soundness are estimated to be suitable for aggregate quality standard in almost all sand, and the absolute dry density is suitable for 66%.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.41 no.4
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• pp.315-324
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• 2015

In this study, we prepared liquid crystal emulsion composed of amphiphilic substance $C_{14-22}$ alcohol, $C_{12-20}$ alkyl glucoside, behenyl alcohol and studied liquid crystal emulsion of properties and in vitro skin permeation. The results of formulation experiments, the clear liquid crystalline structure was observed in the ratio of $C_{14-22}$ alcohol 0.8%, $C_{12-20}$ alkyl glucoside 3.2%, behenyl alcohol 4% in the formulation. The results of physical property measurements, the viscosity of liquid crystal emulsion and O/W emulsion applied as a control group was respectively $1871.26{\sim}1.15Pa{\cdot}s$, $1768.69{\sim}1.14Pa{\cdot}s$ and the shear stress of O/W emulsion was 178.68 ~ 909.18 Pa, that of liquid crystal emulsion was 190.45 ~ 919.38 Pa. The storage modulus of O/W emulsion was 3428.53 ~ 9157.45 Pa, that of liquid crystal emulsion was 4487.82 ~ 8195.59 Pa. The tan (delta) value of O/W emulsion which means a ratio of viscosity to elasticity was 0.43 ~ 0.19, and that of liquid crystal emulsion was 0.23 ~ 0.25. The water content value on the skin for liquid crystal emulsion was significantly higher from 1 h to 6 h compared with that of O/W emulsion and the transepidermal water loss on the skin was significantly superior in skin moisture loss suppression from 30 min to 4 h compared with that of O/W emulsion. The results of skin permeation using glycyrrhizic acid, the result of skin permeation amount of liquid crystal emulsion for 24 h was $64.58{\mu}g/cm^2$, that of O/W emulsion was $37.07{\mu}g/cm^2$, that of butylene glycol solution was $41.05{\mu}g/cm^2$. Hourly permeability results, it is showed that skin penetration effect of the liquid crystal emulsion increases after 8 h. These results suggest that liquid crystal emulsions are effective for skin moisturizing effect and function as potential efficacy ingredient delivery system for the transdermal delivery.

• Journal of the Korean Society of Food Science and Nutrition
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• v.42 no.11
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• pp.1848-1856
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• 2013

This study is designed to examine the change in physical properties of extruded brown rice-vegetable mix at different temperatures and $CO_2$ gas injections. Moisture content and screw speed were fixed to 27% and 100 rpm respectively. Die temperatures and $CO_2$ gas injections were adjusted to 60, 80, $100^{\circ}C$ and 0, 150 mL/min, respectively. The ratio of ${\alpha}$-brown rice, brown rice and sugars (oligosaccharides and palatinose) was fixed to 25, 50 and 16%, respectively. Green tea, tomato and pumpkin powder were blended individually at 9%. Specific mechanical energy (SME) input decreased as die temperature for each vegetable addition increased. All extrudates decreased in density and breaking strength, but increased in specific length and water soluble index as $CO_2$ gas injection increased. Elastic modulus decreased as the die temperature and $CO_2$ gas injection increased. Extruded green tea mix with $CO_2$ gas injection at 150 mL/min was larger pore size and higher amount of pore than the tomato and pumpkin extrudates with $CO_2$ gas injection. Cold extrusion with $CO_2$ gas injection at $60^{\circ}C$ die temperature could be applicable for making Saengsik (uncooked food).