• 한국안전학회지
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• 제32권3호
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• pp.41-47
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• 2017

Recent studies have shown that there are various systems which can be used to monitor hazardous area in a debris flow location, but lack of methodological research on the exact location where each instrument should be installed has hindered the success of this systems. The objective of this study is to suggest the measurement system for monitoring debris-flow and propose the effective method to determine location of measurement system. Previously studied, from 1991 to 2015, were referred and the applied ratio of every instrument was investigated. The measurement information was divided into 8 categories including rainfall, debris-flow velocity, displacement, fluid pore pressure, ground vibration, image processing, impact force and peak flow depth. The result of this study revealed that the most applied instruments to be rain gauge and geophone for measuring average rainfall and ground vibration respectively. The Analytic Hierarchical Process (AHP) method was selected to determine installation location of instrument and the weighting factors were estimated through fine content, soil thickness, porosity, shear strength, elastic modulus, hydraulic conductivity and saturation. The soil thickness shows highest weights and the fine content relatively demonstrates lowest weights. The score of each position can be calculated through the weighting factors and the lowest score position can be judged as the weak point. The weak point denotes the easily affecting area and thus, the point is suitable for installing the measurement system. This study suggests a better method for safely managing the debris-flow through a precise location for installing measurement system.

• 대한의용생체공학회:의공학회지
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• 제34권3호
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• pp.111-116
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• 2013

Finite element analysis(FEA) has been extensively applied in the analyses of biomechanical properties of stents. Geometrically, a closed-cell stent is an assembly of a number of repeated unit cells and exhibits periodicity in both longitudinal and circumferential directions. This study concentrates on various parameters of the FEA models for the analysis of drug-eluting biodegradable polymeric stents for application to the treatment of coronary artery disease. In order to determine the mechanical characteristics of biodegradable polymeric stents, FEA was used to model two different types of stents: tubular stents(TS) and helicoidal stents(HS). For this modeling, epigallocatechin-3-O-gallate (EGCG)-eluting poly[(L-lactide-co-${\varepsilon}$-caprolactone), PLCL] (E-PLCL) was chosen as drug-eluting stent materials. E-PLCL was prepared by blending PLCL with 5% EGCG as previously described. In addition, the effects of EGCG blending on the mechanical properties of PLCL were investigated for both types of stent models. EGCG did not affect tensile strength at break, but significantly increased elastic modulus of PLCL. It is suggested that FEA is a cost-effective method to improve the design of drug-eluting biodegradable polymeric stents.

• 대한토목학회논문집
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• 제13권5호
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• pp.99-107
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• 1993

본 논문에서는 콘크리트 균열 사이의 인장강성 효과를 고려한 임의의 기하하적 형상을 갖는 철근 콘크리트 쉘을 해석하기 위하여 재료비선형 유한요소 프로그램을 작성하였다. 본 논문은 연속적인 컴퓨터 해석으로 탄성, 비탄성 및 극한 범위에서의 철근과 콘크리트의 응력은 물론, 하중-변위 응답과 균열전파를 추적할 수 있었다. 골재억물림과 철근의 다울작용을 포함하는 유효전단계수를 평가하기 위하여 균열상태의 전단유지계수를 도입하였다. 콘크리트는 인장에서는 취성으로 압축에서는 탄소성으로 가정하였다. 콘크리트의 소성거동은 Drucker-Prager 항복기준과 결합유동법칙에 따르는 것으로 가정하였다. 철근은 Von Mises 항복기준으로 가정하였으며 등가의 두께를 가지는 철근층으로 모델화 하였다. 수치해석을 위하여는 증분형접선강성도 방법을 사용하였다. 수치예제를 제시하여 본 연구결과를 Hedgren의 실험 결과와 Lin의 수치해석과 비교하였다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.152-152
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• 2017

Titanium and its alloys have been widely used for biomedical applications. However, the use of the Ti-6Al-4V alloy in biomaterial is then a subject of controversy because aluminum ions and vanadium oxide have potential detrimental influence on the human body due to vanadium and aluminum. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element,such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}$-stabilizer and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Silicon (Si) and magnesium (Mg) has a beneficial effect on bone. Si in particular has been found to be essential for normal bone and cartilage growth and development. In vitro studies have shown that Mg plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. Therefore, in this study, Si and Mg coatings on the hydroxyapatite film formed Ti-29Nb-xHf alloys by plasma electrolyte oxidation has been investigated using several experimental techniques. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. The electrolyte was Si and Mg ions containing calcium acetate monohydrate + calcium glycerophosphate at room temperature. The microstructure, phase and composition of Si and Mg coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.335-335
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• 2011

Instability of a thin film attached to a compliant substrate often leads to emergence of exquisite wrinkle patterns with length scales that depend on the system geometry and applied stresses. However, the patterns that are created using the current techniques in polymer surface engineering, generally have low aspect ratio of undulation amplitude to wavelength, thus, limiting their application. Here, we present a novel and effective method that enables us to create wrinkles with a desired wavelength and high aspect ratio of amplitude over wavelength as large as to 2.5:1. First, we create buckle patterns with high aspect ratio of amplitude to wavelength by deposition of an amorphous carbon film on a surface of a soft polymer poly(dimethylsiloxane) (PDMS). Amorphous carbon films are used as a protective layer in structural systems and biomedical components, due to their low friction coefficient, strong wear resistance against, and high elastic modulus and hardness. The deposited carbon layer is generally under high residual compressive stresses (~1 GPa), making it susceptible to buckle delamination on a hard substrate (e.g. silicon or glass) and to wrinkle on a flexible or soft substrate. Then, we employ glancing angle deposition (GLAD) for deposition of a high aspect ratio patterns with amorphous carbon coating on a PDMS surface. Using this method, pattern amplitudes of several nm to submicron size can be achieved by varying the carbon deposition time, allowing us to harness patterned polymers substrates for variety of application. Specifically, we demonstrate a potential application of the high aspect wrinkles for changing the surface structures with low surface energy materials of amorphous carbon coatings, increasing the water wettability.

• Elastomers and Composites
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• 제20권1호
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• pp.25-39
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• 1985

Elastomer-filler interaction in terms of characterization of filler effects was studied using natural rubber(NR) loaded with kaolin fillers modified with sodium polyphosphate and poly(maleic anhydride), respectively. Kaolins modified with sodium polyphosphate or poly(maleic anhydride) show adhering characteristics by Kraus plot. Reinforcement activity according to Cunneen-Russell method is given by those fillers, in which sodium polyphosphate-treated kaolin presents more favorable results than that treated with poly(maleic anhydride) with respect to adhesion constant, reinforcement extent, elastic constant, and crosslink density. When applied to Blanchard's linkage reinforcement theory, NR vulcanizates loaded with kaolin modified with sodium polyphosphate meet the requirements for both approximate linkage reinforcement(${\psi}'$) of 1.02 to 4.94 and accurate linkage reinforcement($\psi$) of 1.00 to 1.18, representing the values of effective wetting($C_{\psi}$) for 0.001 to 0.029 and intrinsic linkage reinforcement(${\psi}_0$) for 1.015 to 1.124, respectively, whille negligible linkage reinforcement is shown by NR vulcanizates loaded with kaolin treated with poly(maleic anhydride). Dynamic storage modulus(G') given by surface modified kaolins presents more favorable crosslink density rates of $2.260{\times}10^{-5}\;mole/cm^3-min$. for sodium polyphosphate treated kaolin and $1.305{\times}10^{-5}\;mole/cm^3-min$. for poly(maleic anhydride) treated kaolin, respectively, compared to untreated kaolin showing the rate of $1.033{\times}10^{-5}\;mole/cm^3-min$.

• 한국전산구조공학회논문집
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• 제21권6호
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• pp.597-605
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• 2008

본 논문에서는 지진으로부터 구조물을 효과적으로 보호하기 위하여 MR 엘라스토머(MRE)를 이용한 새로운 형태의 스마트 기초격리 시스템을 제안하고, 이에 대한 내진성능을 파악하였다. MRE는 자성물질을 포함한 실리콘 혹은 고무로써 자기장에 의해 강성이 변하는 스마트 재료이다. 기초격리 시스템은 토목 및 건축분야에서 구조물의 내진성능 향상을 위해 가장 널리 쓰이는 장치로 지반과 구조물을 격리시켜 구조물에 가해지는 입력 하중을 감소시켜주는 장치이다. 기존 수동형태의 기초격리 장치는 다양한 입력하중에 대한 적응성이 부족하고 기초격리 장치에서의 과도한 변위 등의 단점이 있는 반면, 새로 제안한 시스템은 제어 가능한 강성범위가 넓어 이를 개선할 수 있다. MRE를 이용한 기초격리 장치의 성능을 확인하기 위하여 기초격리 장치를 도입한 단층 및 5층의 건물에 대해 다양한 역사지진 하중을 이용하여 수치해석을 수행하였다. 수치해석 결과, 제안된 시스템은 기존 수동형태의 시스템에 비해 구조물의 응답 및 기초격리장치의 변위를 감소시키는 데 탁월한 효과가 있음을 확인하였다.

• 한국건축시공학회지
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• 제13권4호
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• pp.351-359
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• 2013

고로슬래그는 콘크리트의 적용시 효율적인 가치향상과 관련하는 많은 장점도 있으나, 고로슬래그의 사용량 증대에 따른 부작용도 나타나고 있다. 따라서 고로슬래그 미분말의 활용성 증대를 위해 High Volume Slag를 자극제 종류별, 치환율별, 조강제 혼입율별, NaOH, $Na_2SiO_3$ 혼합사용시, 폐알칼리자극제 혼입율별 특성을 알아보기 위해 실험하였다. 실험결과, 압축강도의 경우 수산화나트륨을 제외한 모든 알칼리자극제에서 치환율이 증가함에 따라 강도가 증진되었다. 알칼리자극제 중 규산나트륨이 동탄성계수와 흡수율 등에서 높게 나타났으며, 조강제의 경우 혼입율 1.5%와 고로슬래그 치환율 75%가 높은 강도증진을 나타내었다. 폐알칼리 자극제의 경우 모든 실험에서 각기 다른 결과를 나타내었다.

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.93-105
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• 2022

The brittleness of concrete can be overcome by fiber reinforcement that controls the crack mechanisms of concrete. Corrosion-related durability issues can be prevented by synthetic fibers (SFs), while macro synthetic fibers have proven to be particularly effective to provide ductility and toughness after cracks. This experimental study has been performed to investigate the comparative flexural and mechanical behavior of four different macro-synthetic fiber-reinforced concretes (SFRCs). Two polyamide fibers (SF1 and SF2) with different aspect ratios and two different polypropylene fiber types (SF3 and SF4) were used in production of SFRCs. Four different SFRCs and reference concrete were compared for their influences on the toughness, compressive strength, elastic modulus, flexural strength, residual strength and splitting tensile strength. The outcomes of the study reveal that the flowability of reference mixture decreases after addition of SFs and the air voids of all SFRC mixtures increased with the addition of macro-synthetic fibers except SFRC2 mixture whose air content is the same as the reference mixture. The results also revealed that with the inclusion of SFs, 11.34% reduction in the cube compressive strength was noted for SFRC4 based on that of reference specimens and both reference concrete and SFRC exhibited nearly similar cylindrical compressive strength. Results illustrated that SFRC1 and SFRC4 mixtures consistently provide the highest and lowest flexural toughness values of 36.4 joule and 27.7 joule respectively. The toughness values of SFRC3 and SFRC4 are very near to each other.

• 한국지반공학회논문집
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• 제22권4호
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• pp.85-94
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• 2006

본 논문에서는 고결(Cementation)에 의한 모래의 비배수 거동변화를 파악하기 위하여 석고를 고결유발제로 사용한 시료를 조성한 후 등방삼축시험(CIU)을 실시하였으며, 상대밀도 및 고결정도에 따른 거동 양상을 분석하였다. 연구결과 모래의 고결은 항복강도$(q_y)$, 항복시 할선탄성계수$(E_y)$, 첨두마찰각$(\Phi_p)$의 상당한 증가를 유발시키고, 상대밀도보다 모래의 거동에 더 큰 영향을 끼치는 것으로 확인되었다. 그러나 고결결합이 파괴된 이후, 모래의 거동은 고결보다는 상대밀도의 영향을 더 크게 받는 것으로 나타났다. 또한 고결결합에 의한 압축성 감소는 간극수압 발생율을 감소시켜 고결모래의 유효응력 경로가 미고결 모래의 전응력 경로쪽으로 편향되어 발생하였다. 고결결합이 파괴되기 전에는 다일레이션 경향이 감소하지만, 결합이 파괴된 후에는 미고결 모래보다 더 큰 다일레이션 경향이 유발되었다.