• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.309-313
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• 2008

We studied the sapphire and germanium fibers to determine which optical fiber best transmits Erbium:YAG laser for intracorporeal lithotripsy. Human calculi were ablated with an Erbium:YAG laser in contact mode using two fibers. Optical outputs at the distal end of fibers were measured before and after laser lithotripsy. Upon the irradiation on the calculus with the 50 mJ and 100 mJ pulse energy, the output energy at the distal end of germanium fiber declined to approximately 50% of the input energy. For the sapphire fiber, the output energy at the distal end remained unchanged with 100 mJ input energy; however the output energy had dropped to 50% for 200 mJ input energy. In order to examine how the types of target tissue affect the fiber damage, the sapphire fiber was tested for the irradiation on soft tissue and water as well. No energy decline was observed during soft tissue and water irradiation. We also characterized ablation craters with both optical fibers. Both fibers produced similar craters on calculi in terms of depth and diameter. Sapphire fibers are better suited than germanium fibers for Erbium:YAG lithotripsy in terms of the fiber damage.

• Journal of the Optical Society of Korea
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• v.13 no.4
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• pp.416-422
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• 2009

We have demonstrated a highly efficient cladding-pumped ytterbium-doped fiber laser, generating $>$2.1 kW of continuous-wave output power at 1.1 μm with 74% slope efficiency with respect to launched pump power. The beam quality factor ($M^2$) was better than 1.2. The maximum output power was only limited by available pump power, showing no evidence of roll-over even at the highest output power. We present data on how the beam quality depends on the fiber parameter, based on our current and past fiber laser developments. We also discuss the ultimate power-capability of our fiber in terms of thermal management, Raman nonlinear scattering, and material damage, and estimate it to 10 kW.

• International Journal of Concrete Structures and Materials
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• v.7 no.3
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• pp.175-182
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• 2013

A damage-based approach for the performance-based seismic assessment of reinforced concrete frame structures is proposed. A new methodology for structural damage assessment is developed that utilizes response information at the material level in each section fiber. The concept of the damage evolution is analyzed at the section level and the computed damage is calibrated with observed experimental data. The material level damage parameter is combined at the element, story and structural level through the use of weighting factors. The damage model is used to compare the performance of two typical 12-story frames that have been designed for different seismic requirements. A series of nonlinear time history analyses is carried out to extract demand measures which are then expressed as damage indices using the proposed model. A probabilistic approach is finally used to quantify the expected seismic performance of the building.

• Advanced Composite Materials
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• v.16 no.2
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• pp.115-134
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• 2007

This study proposes two new approaches for identifying damage patterns in a holed CFRP cross-ply laminate using an embedded fiber Bragg grating (FBG) sensor. It was experimentally confirmed that the reflection spectrum from the embedded FBG sensor was significantly deformed as the damage near the hole (i.e. splits, transverse cracks and delamination) extended. The damage patterns were predicted using forward analysis (a damage analysis and an optical analysis) with strain estimation and the proposed damage-identification method as well as the forward analysis only. Forward analysis with strain estimation provided the most accurate damage-pattern estimation and the highest computational efficiency. Furthermore, the proposed damage identification significantly reduced computation time with the equivalent accuracy compared to the conventional identification procedure, by using damage analysis as the initial estimation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.905-906
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• 2013

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.438-444
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• 2019

In this study, the effect of polypropylene fiber on the freeze-thaw damage of mortar was evaluated experimentally. The effects of the reinforcing of polypropylene fiber on the compressive and bending performance of mortar after 300 cycles of freeze-thaw test were evaluated by comparing the normal mortar and the mortar with polyvinyl alcohol fiber. In addition, the mass loss, relative dynamic elastic modulus, and cumulated pore volume of mortar were measured by each cycle of freeze-thaw test. As a result, it was confirmed that the fiber reinforced mortar, regardless of the fiber type, was effective not only in maintaining the performance of the compressive strength and the bending strength but also suppressing the mass loss after the freeze-thaw test of 300 cycles. Meanwhile, it was confirmed that not only polyvinyl alcohol fibers but also polypropylene fibers can effectively act to suppress the damage of the mortar by freeze-thaw. However, in order to improve the freeze-thaw resistance of mortar mixed with polypropylene fiber, it is necessary to increase the bonding performance with the cement matrix which can be expected from polyvinyl alcohol fiber.

• Textile Coloration and Finishing
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• v.22 no.4
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• pp.373-379
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• 2010

The laboratory inspection and analysis of several types of ropes such as edge tensile test, D/d tensile test and abrasion test were carried out in order to investigate the abrasion degradation by external damage and to obtain the fundamental data for measurement against the abrasion. PET ropes were socketed and evaluated under tensile testing. A yarn-on-yarn abrasion test machine has been developed to study the damage and failure associated with rubbing between fiber surfaces. The abrasion test method consists of sliding a length of interwrapped yarn against itself in a reciprocating fashion, either dry or immersed in liquid. It has also been adapted to measure yarn-on-yarn friction. The influence of spin finish on yarn friction and abrasion was investigated extensively. This study indicates that finish has a major effect not only on yarn performance but also on rope performance under the marine environment.

• Journal of the Korean Society of Clothing and Textiles
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• v.2 no.2
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• pp.237-243
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• 1978

Dermatophytes such as Trichophyton mentagrophytes, Trichophyton rubrum and Epidermophyton floccosum are used in this study to confirm (a) The Dermatophytes could utilize the wool, cotton and nylon fiber as a nutrient source. (b) The degree of damage of fibers by the Dermatophytes growth. The results of the experiment are summarized as follows; 1. Dermatophytes could not utilize the wool, cotton and nylon fiber directly as a nutrient source without the exogenously applied nutrients. 2. It was presumed that Dermatophytes could utilize the knitted wool fabric as their nutrient source when nutrient was exogenously applied. since the knitted wool fabric was greatly damaged by T. mentagrophytes and T. rubrum growth. 3. The tensile strength of knitted wool fabric was significantly decreased by T. mentagrophytes and T. rubrum, but not by E. floccosum. However, the tensile strength of knitted nylon fabric was not particularly affected by the Dermatophytes. 4. The burst strength of knitted wool fabric was decreased by T. mentagrophytes ($77\%$). T. rubrum ($53\%$). and E. floccosum ($15\%$). Though the burst strength of knitted cotton fabric was decreased by Dermatophytes about $20\%$, that of knitted nylon fabric was not affected. 5. Observing the damaged wool fiber by scanning microscope, the inner part of wool fiber was permeated by T. mentagrophytes and T. rubrum.

• Tunnel and Underground Space
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• v.20 no.5
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• pp.378-389
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• 2010

Submarine tunnels are affected by the surrounding environments more than regular tunnels. Especially, they are often vulnerable to damage by salt in seawater. Seawater is more likely to affect reinforcing rods and steel fibers than concrete. Recently the usage of anti-corrosive fibers increases in the tunnel which is subject to the possibility of damage. By comparing the capability of polypropylene fibers with that of steel fibers, the proper mixture ratio is decided and the supporting capability of polypropylene fibers was tested using round panel and beam specimens. The results of this study can be of great use in selecting the fiber material and designing of fiber reinforced shotcrete of submarine tunnels.

• Computers and Concrete
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• v.21 no.6
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• pp.669-679
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• 2018

In this paper the behavior of reinforced concrete (RC) beam-column connections under cyclic loading was analyzed. The specimens, manufactured in a reduced-scale were made of (a) recycled aggregate concrete (RAC) by replacing 30% of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) and (b) RAC incorporating Polyethylene terephthalate (PET) fiber i.e., PET fiber-reinforced concrete (PFRC) at the joint region. PET fiber (aspect ratio=25) of 0.5% by weight of concrete used in the PFRC mix was obtained by hand cutting of post-consumer PET bottles. A reference specimen was also prepared using 100% of NCA and subjected to similar loading sequence. Comparing the results the structural behavior under cyclic loading of RAC specimens are quite similar to the reference specimens. Damage tolerance, load resisting capacity, stiffness degradation, ductility, and energy dissipation of the RAC specimens enhanced due to addition of PET fibers at the joint region. PFRC specimens also presented a lower damage indices and higher principal tensile stresses as compared to the RAC specimens. The results obtained gave experimental evidence on the feasibility of RAC for structural use. Using PET fibers as a discrete reinforcement is recommended for improving the seismic performance of RAC specimens.