• Journal of the Korean Geosynthetics Society
• /
• v.18 no.1
• /
• pp.67-77
• /
• 2019

The grouting method is utilized to reinforce and waterproof poor grounds, enhance the bearing capacity of structures damaged resulting from settlement due to elevation and vibration or differential settlement, and for cutoff. The purpose of this research is to enhance the compressive strength of grout materials by using aramid fiber and develop a high-strength ground improvement method by using blast furnace slag powder. In this regard, this study has conducted a uniaxial compression test after checking the high charge (higher than 50%) of the ratio of blast furnace slag powder and cement at 100:0, 70:30 and 40:60%, adding the aramid mixture based on 0, 0.5 and 1.0% of the cement and furnace slag powder weight and creating sand gels based on surface oiling rate of 0.7 and 1.2%. For the environmental review evaluation, a heavy metal exudation test and a pH test measurement have been conducted. The experiment results showed that 1% increase of aramid fiber led to 1.3 times greater uniaxial compression intensity. As for the hexavalent chrome, a 30% increase in blast furnace slag powder led to approximately 50% decrease in heavy metal exudation. However, the pH test revealed that a 30% increase in blast furnace slag powder resulted in approximately 0.5 increase in pH. Further research on the pH part is needed in the future.

• Journal of Rhinology
• /
• v.25 no.2
• /
• pp.86-90
• /
• 2018

Background and Objectives: Although polyvinyl acetate ($Merocel^{(R)}$) has been widely used as a packing material after septoplasty, removable nasal packing can increase patient discomfort, local pain, and pressure. Furthermore, the removal of nasal packing has been described as the most uncomfortable and distressing feature associated with septoplasty. The purpose of this study was to investigate the efficacy of polyvinyl acetate with carboxymethyl cellulose sheet ($Rhinocel^{(R)}$) nasal packing on patient subjective symptoms, degree of bleeding, hemostasis, and wound healing following septoplasty. Subjects and Method: Forty patients with nasal septum deviation requiring septoplasty were included. Following surgery, one nasal cavity was packed with $Rhinocel^{(R)}$ and the other one with $Merocel^{(R)}$. Patient subjective symptoms while the packing was in situ, hemostatic properties, pain on removal, degree of bleeding on removal, duration of hemostasis after removal, postoperative wound healing, and the cost of the pack were evaluated. Results: Although the two types of packing materials were equally effective in controlling postoperative bleeding after septoplasty, $Rhinocel^{(R)}$ was significantly more comfortable while in situ and less painful on removal than $Merocel^{(R)}$, which was associated with significantly more bleeding on removal and so more time was needed to control hemorrhage. There was no significant difference in postoperative wound healing or pack cost. Conclusion: The use of $Rhinocel^{(R)}$ after septoplasty has less discomfort, greater patient satisfaction, and less bleeding on removal with no adverse reactions compared to $Merocel^{(R)}$ packing. Therefore, $Rhinocel^{(R)}$ may be a useful packing material after septoplasty.

• Composites Research
• /
• v.35 no.3
• /
• pp.139-146
• /
• 2022

In this study, we study fabrication methods suitable for CNT fibers-based composite. We try to fabricate a composite material using a small amount of CNT fiber preparation of woven fabrics or stitched unidirectional fabrics consisting of CNT fiber is not achievable currently. The composite materials on the basis of CNT fibers have been mainly manufactured filament winding method due to productivity issues and difficulties in composite processes. We develop a new method to prepare CNT fibers-based composite using resin infiltrated CNT fibers-based films. Because CNT fibers have numerous nanopores inside, unnecessary resin can remain after curing and decrease the mechanical properties of the composites. To remove the excess resin, pressure should be applied during the process, but the pressure applied through VaRTM was not enough to remove the excess resin. To obtain the composite with high ratio of CNT fibers, higher pressure using hot press machine and foams next to the resin-infiltrated CNT fibers are necessary. We can obtain the composite having a mass ratio of 58.5 wt% based on the new suggested method and diluted epoxy. The specific strength of the composite reach 0.525 N/tex. This study presents a new process method that can be applied to the manufacturing of CNT fiber composite materials in the future.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.32 no.5
• /
• pp.191-198
• /
• 2022

Zirconia and titanium alloys, which are mainly used for dental implant materials, have poor osseointegration and osteogenesis abilities due to their bioinertness with low bioactivity on surface. In order to improve their surface bioinertness, surface modification with a bioactive material is an easy and simple method. In this study, akermanite (Ca₂MgSi₂O₇), a silicate-based bioceramic material with excellent bone bonding ability, was synthesized by a solid-state reaction and investigated its bioactivity from the analysis of surface dissolution and precipitation of hydroxyapatite particles in SBF solution. Calcium carbonate (CaCO₃), magnesium carbonate (MgCO₃), and silicon dioxide (SiO₂) were used as starting materials. After homogeneous mixing of starting materials by ball milling and the drying of at oven, uniaxial pressing was performed to form a compacted disk, and then heat-treated at high temperature to induce the solid-state reaction to akermanite. Bioactivity of synthesized akermanite disk was evaluated with the reaction temperature from the immersion test in SBF solution. The higher the reaction temperature, the more pronounced the akermanite phase and the less the surface dissolution at particle surface. It resulted that synthesized akermanite particles had high bioactivity on particle surface, but it depended on reacted temperature and phase composition. Moderate dissolution occurred at particle surfaces and observed the new precipitated hydroxyapatite particles in synthetic akermanite with solid-state reaction at 1100℃.

• Korean Journal of Optics and Photonics
• /
• v.33 no.5
• /
• pp.218-229
• /
• 2022

We have investigated reliable inspection methods for finding the defects generated during the manufacturing process of lightweight, large-aperture satellite telescope mirrors using silicon carbide, and we have measured the basic physical properties of the mirrors. We applied the advanced ceramic material (ACM) method, a combined method using liquid-silicon penetration sintering and chemical vapor deposition for the carbon molded body, to manufacture four SiC mirrors of different sizes and shapes. We have provided the defect standards for the reflectors systematically by classifying the defects according to the size and shape of the mirrors, and have suggested effective nondestructive methods for mirror surface inspection and internal defect detection. In addition, we have analyzed the measurements of 14 physical parameters (including density, modulus of elasticity, specific heat, and heat-transfer coefficient) that are required to design the mirrors and to predict the mechanical and thermal stability of the final products. In particular, we have studied the detailed measurement methods and results for the elastic modulus, thermal expansion coefficient, and flexural strength to improve the reliability of mechanical property tests.

• Journal of the Korean Institute of Gas
• /
• v.25 no.2
• /
• pp.64-71
• /
• 2021

Research on polymer matrix composites with excellent molding processability and mechanical properties in the automotive field including hydrogen fuel cell electric vehicles is expanding to Computer-Aided Engineering (CAE) to support the design of materials with specific mechanical properties. CAE automation requires the prediction of the mechanical properties and behavior of materials. Unlike single materials, the mechanical properties prediction of polymer matrix composites is difficult to explain with formulas because the mechanical behavior is complicated to be explained only by the relationship between the matrix and the filler. In this study, the stress-strain curve according to the composition of polymer matrix composites, which was difficult to predict due to its sensitivity to large plastic deformation and composition, was predicted based on machine learning of the test data. The developed model finds a complex correlation between matrix and filler types and compositions, and predicts the total stress-strain curve meaningfully even in the absence of learned test data. It is expected that the material design AI system can be completed in the future based on the developed model that predicts the mechanical properties of polymer matrix composites even for the combination and composition that have not been learned.

• Composites Research
• /
• v.35 no.5
• /
• pp.322-327
• /
• 2022

Composite lap joints have been extensively used due to their excellent properties and the demand for light structures. However, due to the weak mechanical properties in the thickness direction, the lap joint is easily fractured. various reinforcement methods that delay fracture by dispersing stress concentration have been applied to overcome this problem, such as z-pinning and conventional stitching. The Z-pinning is reinforcement method by inserting metal or carbon pin in the thickness direction of prepreg, and the conventional stitching process is a method of reinforcing the mechanical properties in the thickness direction by intersecting the upper and lower fibers on the preform. I-fiber stitching method is a promising technology that combines the advantages of both z-pinning and the conventional stitching. In this paper, the static and fatigue strengths of the single-lap joints reinforced by the I-fiber stitching process were evaluated. The single-lap joints were fabricated by a co-curing method using an autoclave vacuum bag process and I-fiber reinforcing effects were evaluated according to adherend thickness and stitching angle. From the experiments, the thinner the composite joint specimen, the higher the I-fiber reinforcement effect, and Ifiber stitched single lap joints showed a 52% improvement in failure strength and 118% improvement in fatigue strength.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.10
• /
• pp.5-11
• /
• 2007

This paper is to investigate the removal of the smear at elevated temperatures. This study utilized both small cylinder cell and large consolidometer apparatus to investigate the combination of PVD with heat and without heat. Two types of heaters are used in this study. The heater drain made of copper tube is used for all tests except large consolidometer and flexible wire heater is used for large consolidometer. Specimens demonstrated volume contraction upon heat and without heat. This contraction is dependent on temperature magnitude. When the specimen is heated, the magnitude of settlements is higher and rate of consolidation is faster. After treatment using PVD combined without heat and with heat for undisturbed specimens the $C_h$ values obtained were $3.45m^2/yr$ and $3.83m^2/yr$, respectively, from $3.2m^2/yr$ before treatment. The $K_h/K_s$ ratios were 3 for the specimen without heat and 2 for the specimen with heat. Similarly, in reconstituted specimens without heat and with heat, the $C_h$ values were $2.1m^2/yr$ and $2.5m^2/yr$ with $K_h/K_s$ ratios of 1.75 and 1.5, respectively.

• The Journal of Engineering Geology
• /
• v.33 no.4
• /
• pp.573-586
• /
• 2023

Joints or weak planes can induce anisotropy in the strength and deformability of fractured rock masses. Comprehending this anisotropic behavior is crucial to engineering geology. This study used plaster as a friction material to mold specimens with a single joint. The strength and deformability of the specimens were measured in true triaxial compression tests. The measured results were compared with three-dimensional numerical analysis based on the distinct element method, conducted under identical conditions, to assess the reliability of the modeled values. The numerical results highlight that the principal stress conditions in the field, in conjunction with joint orientations, are crucial factors to the study of the strength and deformability of fractured rock masses. The strength of a transversely isotropic rock mass derived numerically considering changes in the dip angle of the joint notably increases as the intermediate principal stress increases. This increment varies depending on the dip of the joint. Moreover, the interplay between the dip direction of the joint and the two horizontal principal stress directions dictates the strength of the transversely isotropic rock mass. For a rock mass with two joint sets, the set with the steeper dip angle governs the overall strength. If a rock bridge effect occurs owing to the limited continuity of one of the joint sets, the orientation of the set with longer continuity dominates the strength of the entire rock mass. Although conventional three-dimensional failure criteria for fractured rock masses have limited applicability in the field, supplementing them with numerical analysis proves highly beneficial.

• Composites Research
• /
• v.36 no.5
• /
• pp.297-302
• /
• 2023

There are several methods for shaping foams, but the most commonly used methods involve the use of resin mixed with a foaming agent, which is then foamed under high temperature and pressure in the case of compression foaming, or foamed under high temperature without applying pressure in the case of atmospheric foaming. The polymers used for foaming require design and analysis of optimal foaming conditions in order to achieve foaming under ambient pressure. Environmentally friendly bio-based polymers face challenges when it comes to foaming on their own, which has led to ongoing research in blending them with resins capable of traditional foam production. This study investigates changes in the characteristics of bio-based polymer-EVA blend foams based on variations in the content of bio-based polymers and explores the optimal foaming conditions according to crosslinking. The correlation between foaming characteristics and mechanical properties of the foams was examined. Through this research, we gained insights into how the content of bio-based polymers affects the properties of foams containing bio-based polymers and identified differences between ambient pressure and high-pressure foaming processes. Additionally, the feasibility of commercializing bio-based polymer-EVA composite foams was confirmed.