• The Journal of Engineering Geology
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• v.21 no.3
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• pp.199-212
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• 2011

To investigate the causes of ground deformation around the Dogye coal waste depot in Samcheok city, Gangwon Province, we undertook a field survey and performed boring tests and a topographic analysis using maps compiled in various years. The results of boring tests and analyses of ground fractures indicate that the thickness of the soil layer ranges from 9 to 28.5 m and that ground deformation has occurred to the $240{\sim}250^{\circ}$ direction. The topographic analysis revealed that the topography of the site has changed continuously due to the dumping of coal waste. The causes of ground deformation, investigated by both field surveys and the topographic analysis, were the thick layer of soil at this site, the loading weight of coal waste, and the excavation at the lower part of the slope.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.301-310
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• 2001

Gypsum blocks with sixteen flaws have been prepared and tested in uniaxial compression. Results from these experiments are compared with observations from the same material with two and three flaws. The results indicate that the cracking pattern observed in specimens wish multiple flaws is analogous to the pattern obtained in specimens with two and three flaws such as initiation and propagation of wing, and secondary cracks and coalescence. Wing cracks initiate at an angle with the flaw and propagate in a stable manner towards the direction of maximum compression. Secondary cracks initiate and propagate in a stable manner. As the load is increased, secondary cracks may propagate in an unstable manner and produce coalescence. Two types of secondary cracks are observed: quasi-coplanar, and oblique secondary cracks. Coalescence is produced by the linkage of two flaws: wing and/or secondary cracks. From the sixteen flaws test, four types of coalescence are observed. Observed types of coalescence and initiation stress of wing and secondary crackle depend on flaw geometries, such as spacing, continuity, flaw inclination angle, ligament angle, and steppings.

• Journal of Conservation Science
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• v.35 no.4
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• pp.279-293
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• 2019

The stone lantern of the Damyang Gaeseonsaji temple site is a cultural heritage built during the Unified Silla period (AD 868). The reason for its value as a cultural property is due to wittern the background and the period created on inscription of the lamp stone engraved by letters. The stone lantern consists of two types of lithic tuffs for the 23 original properties, the replaced stones in 1991, and the biotite granite for its ground stones replaced in 2005. The lithic tuffs selected as the replacement parts in 1991 and 2017 have been examined and got to properties of hardly exposure moisture as well as very similar geochemical characteristics. There were various types of physical deterioration of the stone properties and structural cracks; in particular, on the northern side of the stylobates. Chemical and biological deterioration can be identified as black, white, and brown discolorations as well as by the presence of lichens, bryophytes, and herbaceous plants. In the evaluation of the physical properties of the stone lantern, the mean and maximum ultrasonic velocities were found to be similar in each direction. However, the lowest velocity on the east and south sides were found to be lower than those of other stone properties. It was found that physical damage to the stylobates resulted from water expansion in a freeze-to-thaw phenomena related to water content. Therefore, dismantling repair was carried out in the protection facility to restrict further water supply to the stone as much as possible.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.12-21
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• 1995

The study was performed to study the effects of strain rate on acoustics emission( AE) during bulging test in corrosive environmentsynthetic sea water. The strain rates used were in the range $4 \times 10^{-6}S^{-1}$ to $1 \times 10^{-4} \times S^{-1}$ and the parameters used to evaluate AE signal characteristics were AE hit and amplitude. It can be observed that the cumulative AE hit and average amplitude during fracture process increase highly at decreasing strain rates while the equivalent fracture strain and the crack length of circumferencial direction become decrease. The peak point of AE signal characteristic parameters approach to the first half of test. When the average amplitude per unit equivalent fracture strain was above 20dB, it was definitly observed stress corrosion cracking phenomena. Additional, we knew that the AE test had the possibility to evaluate SCC susceptibility with various strain rates.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.3
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• pp.89-93
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• 2020

Complex warpage behavior of the electronic packages causes internal stress so many kinds of mechanical failure occur such as delamination or crack. Efforts to predict the warpage behavior accurately in order to prevent the decrease in yield have been approached from various aspects. For warpage prediction, silicon is generally treated as a homogeneous material, therefore it is described as showing no warpage behavior due to thermal loading. However, it was reported that warpage is actually caused by residual stress accumulated during grinding and polishing in order to make silicon wafer thinner, which make silicon wafer inhomogeneous through thickness direction. In this paper, warpage behavior of the single-side polished wafer at solder reflow temperature, the highest temperature in packaging processes, was measured using 3D digital image correlation (DIC) method. Mechanism was verified by measuring coefficient of thermal expansion (CTE) of both mirror-polished surface and rough surface.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.922-933
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• 2002

Since the deterioration of concrete bridge decks affect durability, safety, and function, structural rehabilitation of damaged concrete deck that was strengthened with Fiber Reinforced Polymer(FRP) is increasing the latest. But recent studies on the strengthened structures are focused on the static behavior, however only a few studies on the fatigue behavior are performed. In this study, static and fatigue behavior of strengthened deck were peformed on 11 deck specimens strengthened with sheet typed Glass Fiber Reinforced Polymer(GFRP) that were reinforced by two different strengthening methods for the static test. A amount of strengthening material in the each direction such as transverse and longitudinal was adopted experimental variables for the static test and also the stress level of the static maximum load are adopted for the fatigue test. By the results of the experimental study, with respect to the strengthened decks, the resistance effect of crack propagation and effect of stress distribution are improved. In addition, the rate of variation of compliance decreased.

• Fire Science and Engineering
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• v.15 no.1
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• pp.108-115
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• 2001

In this paper, we analyzed the properties change of electric wire when the thermal stress was applied to 600V grade polyvinyl chloride insulated wire (IV). In the structure analysis, normal wire has the properties of direction on the surface, but in case of deteriorated wire at above $400^{\circ}c$, it formed the carbide, the crack and the crystal. The surface composition rate of normal wire was Cu : 100%, but the section composition of the deteriorated wire at $800^{\circ}c$ showed Cu : 78.89%, O : 21.11%. In result of analyzing the differential scanning calory of copper wire, the new reaction peak was observed on the deteriorated wire at above $700^{\circ}c$. In case of the deteriorated wire as $150^{\circ}c$ at the differential thermal analysis, an endothermic reaction appeared at $264^{\circ}c$ lower than the reactive point of normal wire. The occupation rate of oxygen according to the deterioration of copper wire is about 20% at $500^{\circ}c$.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.119-127
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• 1999

The objective of this study is to simulate the fracture behavior of composite structure bonded with more than 2 different cementitious materials. For this, concrete and cement were stacked and bonded in a direction perpendicular to loading and specimens were tested. Each constituent material of concrete and cement was fabricated independently also, and three point bending and indirect tensile tests were carried out for the acquisition of measured values applicable to the proposed model. As a result of comparing theoretical results and experimental ones, it was found that the proposed model derived from fictitious crack theory can be used to predict the fracture behavior of composite structures on the vases of well agreement with experimental results. It was also noted that the degree of improvement of fracture energies and strengths is greatly dependent on the stacking sequence of layers composing of a composite structure. Thus, it can be concluded that brittleness or ductility of a composite structure can be accomplished by a proper arrangement of layers on one's purpose throughout the proposed analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1213-1219
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• 2012

A remote $CO_2$ laser system can rapidly change both the distance and the direction of the laser beam by moving a lens and rotating mirrors. It is then easy to weld complex patterns of weld lines. A conventional spot weld joint specimen and a remote $CO_2$ laser weld joint specimen with complex weld line patterns were prepared and tested both statically and dynamically. The relationships between the fatigue strength, i. e. the maximum cyclic force, and the fatigue life were obtained. The fatigue strength of the tested welded joints at two million cycles was found to be approximately 10% of the static strength. Furthermore, it was observed that the fatigue fracture mode changed with the level of the applied cyclic force. The fatigue crack origins were confirmed as the highest stress points found in the structural analysis. The maximum cyclic stress for different weld patterns converges as the fatigue life approaches two million cycles.

• The Journal of Engineering Geology
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• v.8 no.3
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• pp.275-284
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• 1998

Deformation behavior and microcrack development due to uniaxial compressive cyclic loading in the Pocheon granite were investigated using the ultrasonic velocity measurements and the differential strain analysis(DSA). Most microcracks were developed along the direction parallel to the loading axis. Microcracks developed at the early stage of cyclic loading were formed by propagation of pre-existing cracks. Ultrasonic velocity measurement, DSA and measurement of permanent deformation are good tools to represent microcrack development in rock. Since results from each method are slightly different, microcrack development should be interpreted from all three methods. The magnitude of microcracks developed at the early stage of cyclic loading under 80% loading level is twice compared with those under 70% loading level. The highest volumetric crack strain is about 3000, indicating that the Pocheon granite will fail with 0.3% occupation of microcrack in volume.