• Journal of the Korean Applied Science and Technology
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• v.32 no.4
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• pp.607-615
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• 2015

To investigate the adhesion effect of various kinds and contents of polymeric methylene diphenyl diisocyanates (pMDIs) on adhesion performance, wood adhesives (A-1~5) were synthesized and characterized. As results, when the amount of pMDI increased in adhesives, the dry tensile strength was found to be proportionally increased sustaining at around $16.0{\sim}21.6kgf/cm^2$. The polyurethane (PU) resin, which used M11S as a source of pMDI showed the best wet tensile strength at $11.9kgf/cm^2$ and cyclic boil tensile strength at $8.1kgf/cm^2$, which satisfied the requirement of over $7kgf/cm^2$. Thermal properties of the rice powder (RP) based polyurethane resins were characterized by differential scanning calorimetry (DSC) and Thermal gravimetric analysis (TGA). Thermal stability of polyurethane resins increased to $250^{\circ}C$ with adding pMDIs. The more pMDI (M5S) was added to adhesive, the higher thermal stability of the resin was observed by TGA.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.12
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• pp.113-118
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• 2010

For a present study, woven type carbon fibers were surface-modified by oxygen plasma to improve adhesive strength between carbon fibers and epoxy. The change of hydrophilic properties by the plasma modification was investigated through the contact angle measurement and the calculation of surface energy of carbon fiber due to the oxygen plasma modification. FESEM and XPS analyses were performed to study the chemical and physical changes on the surface of carbon fibers due to the oxygen plasma modification. Pin-on-disk wear tests were conducted under dry condition using unmodified and plasma-modified carbon/epoxy composites to investigate the effect of plasma modification on the wear behavior of woven type carbon/epoxy composites. The results showed that the friction coefficient and the wear rate of plasma-modified carbon/epoxy composites were lower than those of unmodified carbon/epoxy composites, respectively. XPS analysis showed that new functional group of a carbonyl type was created on the carbon fibers by the $O_2$ plasma treatment, which enhanced adhesive strength between carbon fibers and epoxy, leading to improve wear properties

• Journal of the Korea Institute of Building Construction
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• v.8 no.4
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• pp.105-114
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• 2008

This study investigates the saturation level of surface dryness, quantity of adhesive mortar, and the alien substance content of recycled aggregates for concrete to develop an adequate quality testing method for understanding the properties of recycled aggregates, which differ greatly from preexisting aggregates. For tests that measure the saturation level of surface dryness, where detail methods are applied differently according to the tester, various testing methods from across world were compared and analyzed. This study revealed that when measuring the saturation level of surface dryness of a certain sample, aggregates must be supplemented immediately whenever the height of the sample becomes lower than the measuring mold, and allowing the tamper to free fall on the sample will provide the most accurate results. When measuring the quantity of adhesive mortar of recycled aggregates for concrete, an acid solution was used, and since the quantity of adhesive mortar increases as the particle sizes gets smaller, the sample for testing should represent the entire granularity. Sulfuric acid solution is adequate for immersion, and the concentration should be 20% for best results. According to the alien substance content measurement, which was examined by the naked eye, the error range caused by the difference in particle size was neglectable, and therefore the sample should be $2.5{\sim}5.0mm$ in size concerning the accuracy and measuring time. Also, for coarse recycled aggregates, the sample should amount to 1kg for measuring alien substance content by the naked eye, which proves that assortment by the naked eye is the most adequate method for measuring the alien substance content of a recycled aggregate.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.4
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• pp.833-849
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• 1996

The material of choice for functional and esthetic reconstruction of maxillofacial defects is silicone. Silicone has appropriate physical properties for maxillofacial prosthesis but it has weak edge strength. Therefore, a proper combination of silicone and polyurethane sheet is recommended to improve this weakness. Various primers are also used to enhance the adhesive strength between silicone and polyurethane sheet. The purpose of this study was to determine the adhesive strength of silicone and polyurethane sheet. Silicone elastomer mixture was made by admixing MDX4-4210 elastomer (40%) and Silastic Medical Adhesive Type A(60%). This silicone elastomer mixture was attached to polyurethane sheet, using one of three different primers(1205, S-2260, or A-304), treated for 1, 2, 4, 6, and 8 hours. These were then polymerized in room temperature, dry-heat oven or microwave oven. Six specimens per each group, a total of 270 specimens were prepared for final test. The differences of T-peel bonding strengths were then determined by a test. The differences of T-peel bonding strengths were then determined by a test method that was recommended by American Society for Testing and Materials C794-80. The results were statistically analyzed using the ANOVA and Mutiple Range Tests(Tukey' HSD). The reults were as follow. 1. Type of primer, primer reaction time, and methods of polymerization showed significant correlation on the T-peel bonding strengths in adhesiveness between silicone and polyurethane sheet. 2. A-304 primer showed statistically higher in T-peel bonding strength than otehr type of primers except for the polymerization in microwave oven with reaction times of 2, 6 hours(p<0.05). 3. No significant differences in T-peel bonding strength were observed among the polymerization methods. 4. The effect of reaction time by the primer type and polymerization method showed statistically significant differences in bonding strength among different reaction times. And in most cases, reaction time of 1 or 2 hours showed higher T-peel bonding strength.

• Journal of the Korean Wood Science and Technology
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• v.43 no.4
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• pp.528-537
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• 2015

To reuse the waste bone from restaurants or butcher houses, the possibility of using waste bone powder after cooking as a filler for wood adhesives used in manufacturing plywood was investigated. Radiata pine (Pinus radiata D. Don) plywoods were manufactured by using commonly used wood adhesives such as urea-melamine formaldehyde (UMF) resin, urea-formaldehyde (UF) resin, and phenol-formaldehyde (PF) resin and the prepared fillers from cattle bone powder, pig bone powder, and seashell powder. Plywood fabricated by using cattle bone powder, pig bone powder, and seashell powder showed weaker performance in dry and wet glue-joint shear strength and wood failure than those of the plywood with wheat flour. The result showed that it was hard to use only bone powder for the replacement of wheat flour. However, the filler mixed with wheat flour and bone powders showed equivalent dry bonding strength and better water resistance than the wheat flour, indicating that bone powders mixed with wheat flour might be used for the manufacture of plywood. When bone powders were mixed with wheat flour as adhesive fillers the shell powder showed the lowest bonding properties and there was no big difference between the cattle bone powder and the pig bone powder.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.953-956
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• 2008

The present study was to develop a dry PFB method similar to the existing gypsum board construction method in order to apply the existing wet PFB method that uses fire.resistant adhesive. It was found that the existing wet method can produce concrete compressive strength of 80MPa and fire resistance of 3 hours with 30mm PF boards. The goal of development in this study was fire resistance of 3 hours through dry construction of 15mm fire.resistant boards.According to the results of fire resistance test, when the dry PF method was applied, the temperature of the main reinforcing bar was 116$^{\circ}$C in 15mm, 103.8$^{\circ}$C in 20mm, and 94$^{\circ}$C in 25mm, and these results satisfied the current standards for fire resistance control presented by the Ministry of Land, Transport and Maritime Affairs. When a 3.hour fire resistance test was performed and the external properties of the specimen were examined, the outermost gypsum board hardly remained and internal PF board maintained its form without thermal strain.

• Tribology and Lubricants
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• v.30 no.6
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• pp.343-349
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• 2014

Currently, in order to resist the scratching of the fuel rod surface while fabricating the fuel assembly of the light-water nuclear reactor, we use a solution of nitrocellulose, an explosive material, as a dry lubricant along with its solvent. However, the demand for developing safe and harmless aqueous alternative materials for environment-conservation and field-worker safety has increased. In this study, we demonstrate the preparation of a novel aqueous resin composite using a formulation of aqueous polymeric resin, alcoholic solvent, and water. Subsequently, we characterize this composite on the basis of hardness, adhesive property, and water solubility using plates similar to the fuel rod material. The insertion test of a fuel rod coated with the YS-3 composite shows load values of $18.8-20.5kg/cm^2$, which is comparable with $18.8-20.5kg/cm^2$ of the nitrocellulose coating agent. In addition, the depth and width of longitudinal scratches caused by the YS-3 composite test are 50% higher than those of the standard. We can develop a harmless and safe aqueous dry lubricant to replace the existing NC products through field testing of 264 pieces of fuel rods, after producing 350 kg of the YS-3 prototype. The scratch test for the rod surface showed that weight of chip of YS-3 prototype was smaller than that of NC before and after solvent treatment, indicating the properties of YS-3 prototype was comparable to the counterpart.

• Tribology and Lubricants
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• v.9 no.2
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• pp.49-55
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• 1993

The dry sliding wear properties of the sintered Cu-10 wt%Sn bronze alloys reinforced with $SiC_w$ and $SiC_p$ were investigated by a pin-on-disc wear testing machine. The worn surfaces and the cross sections of the wear specimens and the wear debris were observed by SEM to study the effect of the variation of the ceramic phase contents in the composite and the wear condition on the wear behaviors. The wear of bronze matrix was dominated by the adhesive wear. The transition from mild to severe wear was found in the bronze matrix specimens at the applied load higher than 20N where the surface delamination caused the severe wear. The addition of $SiC_w$ and $SiC_p$ reinforcements in the romposites was proved to reduce the wear rate by the matrix strengthening at the applied load higher than 20N. SiC whiskers having a large length to diameter ratio which hold the deformed matrix were effective to hinder the crack propagation near the worn surface. Thus the maximum wear resistance was obtained in the composite reinforced by $SiC_w$ at the higher applied load.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.4
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• pp.398-402
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• 2014

This paper presents the results of a study on the optimal footpad design for vertical climbing on acrylic surfaces with various curvatures used Taguchi methods. For a climbing robot, the adhesion system plays an important role in the climbing process. Only an appropriate adhesion strength will prevent the robot from falling and allow it to climb normally. Therefore, the footpad is a significant parameter for a climbing robot and should be studied. Taguchi methods were used to obtain a robust optimal design, where the design variables were the flat tacky elastomeric shape, area, thickness, and foam thickness of the footpad. Experiments were conducted using acrylic surfaces with various curvatures. An optimized footpad was selected based on the results of the experiments and analysis, and the stability of the wall-climbing robot was verified.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.432-432
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• 2011

Dry adhesion caused by Nanoscale contact comes up to important scientific issue. Herein, we introduce bendable nanohairy locking fastener system with high shear strength and mechanically flexible backing. The polymeric patches like velcro are composed of an array of straight nanohairs with 100 nm diameter and $1{\mu}m$ height. To fabricate high aspect vertical nanohairs, we used UV molding method with appropriately flexible and rigid polyurethane acrylate material on PET substrate. Two identical nanohairy patches are easily merged and locked each other induced by van der Waals force. Because nanohairs can be arrayed with high density ${\sim}4{\times}10^8/cm^2$, we can obtain high shear adhesion force on flat surface (~22 N/$cm^2$). Furthermore, we can obtian nanohairy locking system with maximum shear adhesion ~48 N/$cm^2$ of curved surface due to flexibility of PET substrate. We confirm the tendency that shear adhesion force increases, as radius of curvature increases.