• Composites Research
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• v.25 no.3
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• pp.65-69
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• 2012

The main objective of this study is to investigate the effect of metal z-pinning on the failure behavior of cocured composite single-lap joints. Three different pin diameters (0.3, 0.5, and 0.7 mm) and three pin areal densities (0.5, 2.0, and 4.0%) were examined. The specimens were fabricated by T700-12K-31E#2510 unidirectional prepreg from Toray. Stainless steel pins were used for z-pinning. Test results showed that except one case with extremely low pin density of 0.5%, all other z-pinned joints exhibited lower initial crack stresses than those of the unpinned joint. However the ultimate strength of the z-pinned joint increased up to 45% at most. Furthermore, even after the complete failure of the joint, the z-pins sustained the carried load to a certain degree experiencing large deformation and provided the stable fracture behavior for the composite joint.

• Conservation Science in Museum
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• v.1
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• pp.37-42
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• 1999

Conservation treatment was done for the pottery-stand of Kaya period which was to be exhibited in celebration of the opening of Kimhae National Museum and for the jar of Chinese celadon which was to be exhibited in Korea National Museum's special exhibition "Formation of Ancient States". Through the examinations by naked eyes and under the microscope, condition before treatment, patterns and manufacturing techniques of the objects were observed. According to these examinations, conservation treatments, suitable for each object was finished. As the pottery-stand was damaged severely, the epoxy resin was pasted directly on the broken surface of the pottery to restore the original shape and pattern, color and feeling similar to original state were given to the restored area. Although same restoration material was applied on the celadon, it was not pasted directly on the broken surface of the celadon so that the restored area could be dismantled, and color and feeling were also treated somewhat differently.

• Composites Research
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• v.29 no.2
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• pp.85-89
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• 2016

This paper aims at estimating the fracture behavior at the bonded part of composite material. CFRP is manufactured as the type of TDCB. The static analysis of Mode 1 due to the configuartion factor of m is carried out. Four kinds of specimens have the configuartion factor(m) of 2, 2.5, 3 and 3.5. As the study result, the displacements at specimens are shown to be similar each other in these four cases. At m of 3.5, the reaction force becomes highest as 412 N and is shown to be improved as much as 14% by comparing m of 2. The data on defection of the bonded interface and reaction force are thought to be contributed to the structural design of CFRP and the safe design.

• Composites Research
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• v.19 no.4
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• pp.23-30
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• 2006

In the development of a cryogenic propellant tank, the proper selection of adhesives to bond composite and metal liner is important for the safety of operation. In this study, 3 types of adhesives were tested for the ability to bond CFRP composites developed for cryogenic use and aluminum alloy (Al 6061-T6) for lining the tank using double-lap joint specimens. The double-lap joint specimens were tested inside an environmental chamber at room temperature and cryogenic temperature ($-150^{\circ}C$) respectively to compare the bond strength of each adhesive and fracture characteristics. The material properties with temperature of component materials of double-lap joints were measured. In addition, ABAQUS was used for the purpose of analyzing the experimental results.

• Journal of Adhesion and Interface
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• v.11 no.4
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• pp.149-154
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• 2010

Interfacial evaluation was investigated for single-carbon fiber/phenolic and carbon nanotube (CNT)-phenolic composites by micromechanical technique and electrical resistance measurement combined with wettability test. Compressive strength of pure phenol and CNT-phenolic composites were compared using Broutman specimen. The contact resistance of CNT-phenolic composites was obtained using a gradient specimen by two and four-point methods. Surface energies and wettability by dynamic contact angle measurement were measured using Wilhelmy plate technique. Since hydrophobic domains are formed as heterogeneous microstructure of CNT in the surface, the dynamic contact angle exhibited more than $90^{\circ}$. CNT-phenolic composites exhibited a higher apparent modulus than neat phenolic case due to better stress transferring effect. Work of adhesion, $W_a$ between single-carbon fiber and CNT-phenolic composites exhibited higher than neat phenolic resin due to the enhanced viscosity by CNT addition. It was consistent with micro-failure patterns in microdroplet test.

• Conservation Science in Museum
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• v.13
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• pp.1-11
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• 2012

While the project for registering the unregistered relics that had been stored in the relic storage warehouse was in progress, restoration operations were started for the large size pottery pieces that had been excavated from the Geumgangsa Temple Site and it is attempted to explain the pottery pieces and to introduce the process of the overall conservation treatment. About 600 pieces of large size pottery had been separately stored in more than 40 relic boxes in their original damaged condition without making it possible to figure out their shape, size, usage and quantity at all. Due to the enormous number and weight of the pottery pieces, they were, first of all, pre-classified largely into 6 groups of pottery pieces in consideration of the visible features such as pottery thickness, color sense and glaze brilliance, etc. for each kind of pottery raw material. However, as a result of making them adhere together on a temporary basis, they turned out to be only one piece of pottery in reality. In this restoring process, in order to see if the generally used cyanoacrylate adhesive was in fact safe when a very large, heavy and deformed pottery piece was to be put together, its safeness was checked by examining the adhesion velocity, adhesion strength and dissolution velocity for both from low to high viscosities through preliminary experiments. In order to restore the lost parts after putting the existing pieces together, diversified epoxy resins were used to fit their shapes. Considering that the bottom of the restored relic was shaped to be not flat but round without allowing it to stand alone, an exhibition mount was manufactured so that the relic could be stored stably and used readily for exhibition.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.411-422
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• 2010

Self-sensing on micro-failure, dispersion degree and relating properties, of carbon nanotube(CNT)/epoxy composites, were investigated using wettability, electro-micromechanical technique with acoustic emission(AE). Specimens were prepared from neat epoxy as well as composites with untreated and acid-treated CNT. Degree of dispersion was evaluated comparatively by measuring volumetric electrical resistivity and its standard deviation. Apparent modulus containing the stress transfer was higher for acid-treated CNT composite than for the untreated case. Applied cyclic loading responded well for a single carbon fiber/CNT-epoxy composite by the change in contact resistivity. The interfacial shear strength between a single carbon fiber and CNT-epoxy, determined in a fiber pullout test, was lower than that between a single carbon fiber and neat epoxy. Regarding on micro-damage sensing using electrical resistivity measurement with AE, the stepwise increment in electrical resistivity was observed for a single carbon fiber/CNT -epoxy composite. On the other hand, electrical resistivity increased infinitely right after the first carbon fiber breaks for a single carbon fiber/neat epoxy composite. The occurrence of AE events of added CNT composites was much higher than the neat epoxy case, due to micro failure at the interfaces by added CNTs.

• Economic and Environmental Geology
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• v.35 no.4
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• pp.355-368
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• 2002

The multi-storied Daewonsa stone pagoda (Treasure No. 1112) in the Sancheong, Korea was studied on the basis of deterioration and geological safety diagnosis. The stone pagoda is composed mainly of granitic gneiss, partly fine-grained granitic gneiss, leucocratic gneiss, biotite granite and ceramics. Each rock of the pagoda is highly exfoliated and fractured along the edges. Some fractures in the main body and roof stones are treated by cement mortar. This pagoda is strongly covered with yellowish to reddish brown tarnish due to the amorphous precipitates of iron hydroxides. Dark grey crust by manganese hydroxides occur Partly, and some Part coated with white grey gypsum and calcite aggregates from the reaction of cement mortar and rain. As the main body, roof and upper part of the pagoda, the rocks are developed into the radial and linear cracks. Surface of this pagoda shows partly yellowish brown, blue and green patchs because of contamination by algae, lichen, moss and bracken. Besides, wall-rocks of the Daewonsa temple and rock aggregates in the Daewonsa valley are changed reddish brown color with the same as those of the pagoda color. It suggests that the rocks around the Daewonsa temple are highly in iron and manganese concentrations compared with the normal granitic gneiss which color change is natural phenomena owing to the oxidation reaction by rain or surface water with rocks. Therefore, for the attenuation of secondary contamination, whitening and reddishness, the possible conservation treatments are needed. Consisting rocks of the pagoda would be epoxy to reinforce the fracture systems for the structural stability on the basements.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.229-236
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• 2015

In this study, the resilient modulus test and Light Weight Deflectormeter (LWD) test were conducted to simulate the moving vehicle load for the evaluation of the internal failure of epoxy asphalt pavement. The Measured displacement in the resilient modulus test of epoxy asphalt concrete showed very little residual deformation under repeated loads unlike the conventional asphalt. Therefore, the test results were evaluated as a normal state due to its similarity with elastic deformation. The deflection results from the resilient modulus tests were converted to the surface deflection modulus and the normal range of surface deflection modulus was estimated applying LWD measurement of 1 SIGMA level. Internal failure of pavements were estimated using the suspicious failure range at $60^{\circ}C$ and hysteresis. Internal moisture penetration and a decrease in bonding were observed in partial areas at $140{\mu}m$ of surface deflection. However, the areas showed inflection points in the hysteresis. Field investigation by suggested criterion indicated a high degree of accuracy.

• Conservation Science in Museum
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• v.1
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• pp.75-86
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• 1999

Conservation treatments were done for the gilt bronze saddle accessory excavated from Tomb No. 89 in Kyo-dong, Changnyong in Japanese rule period. The saddle accessory, broken into numerous pieces, was mixed with other remains. Principal aims of conservation treatments were to recover original shape of object and stabilize its material. In the process of treatments manufacturing technique of the remain was examined minutely. Thick layers of corrosion substances were peeled off and numerous pieces were pasted together to restore the original shape. And then the saddle accessory was mounted on an acrylic board to be handled and exhibited safely. In this process, it was confirmed that various ancient techniques of metalic crafts such as amalgam gilding, riveting, piercing, line engraving, stamping, chasing etc. had been used to make the saddle accessory.