• 한국구조물진단유지관리공학회 논문집
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• 제18권3호
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• pp.160-166
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• 2014

본 연구에서는 건축물의 외피를 통해 손실되는 냉난방 에너지를 감소시킬 수 있는 방안으로써, 구조용 콘크리트에 단열성능을 향상시킬 수 있는 할로마이크로스피어 (Hollow Micro Sphere, 이하 HMS)를 사용하였다. 중공구조의 마이크로 크기의 입자인 HMS를 사용한 콘크리트를 실험한 결과는 아래와 같다. HMS의 사용으로 인해 슬럼프에 감소가 나타나 고성능감수제의 사용이 필요할 것으로 판단된다. 공기량은 HMS의 치환율이 증가할수록 감소하는 경향을 보였으며, 압축강도는 HMS의 계면부착력이 형성되지 않는 것에 기인하여 치환율 증가에 따라 감소하는 것으로 나타났다. 열전도율과 단위용적질량은 치환율이 증가할수록 감소하였다. 열전도율은 보통콘크리트 약 30.0~46.5% 감소한 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제18권4호
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• pp.118-125
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• 2014

본 논문은 기존 수중 콘크리트 구조물의 강도관리 및 진단기술의 중요성은 날로 증가함에 따라 개발되고 있는 ROV (Remote Control Vehicle)에 탑재될 수 있는 비파괴 검사 장비를 개발하여 콘크리트 내부의 강도측정을 하고자하였다. 수중화된 슈미트해머와 초음파센서를 통하여 수중에 있는 콘크리트 공시체의 반발경도 및 초음파속도를 계측하여 실제 압축강도 값과 비교하였으며 이를 통하여 수중에서의 강도추정식을 도출하였다. 도출된 3가지 식 중에서 반발경도와 초음파속도를 복합적으로 사용하는 복합식이 가장 정확도가 높았으며 이에 따라 실제 수중에서의 콘크리트의 강도를 추정하고자 할 때 활용 가능성도 높아질 것으로 예상된다.

• 한국재료학회지
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• 제28권5호
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• pp.295-300
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• 2018

Effects of annealing temperature on the microstructure and mechanical properties through thickness of a Cu-3.0Ni-0.7Si alloy processed by differential speed rolling are investigated in detail. The copper alloy with a thickness of 3 mm is rolled to a 50 % reduction at ambient temperature without lubricant and subsequently annealed for 0.5 h at $200-900^{\circ}C$. The microstructure of the copper alloy after annealing is different in the thickness direction depending on the amount of the shear and compressive strain introduced by the rolling; the recrystallization occurs first in the upper roll side and center regions which are largely shear-deformed. The complete recrystallization occurs at an annealing temperature of $800^{\circ}C$. The grain size after the complete recrystallization is finer than that of the conventional rolling. The hardness distribution of the specimens annealed at $500-700^{\circ}C$ is not uniform in the thickness direction due to partial recrystallization. This ununiformity of hardness corresponds well to the amount of shear strain in the thickness direction. The average hardness and ultimate tensile strength has the maximum values of 250 Hv and 450 Mpa, respectively, in the specimen annealed at $400^{\circ}C$. It is considered that the complex mode of strain introduced by rolling directly affects the microstructure and the mechanical properties of the annealed specimens.

• Restorative Dentistry and Endodontics
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• 제22권2호
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• pp.739-750
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• 1997

Treatment of root perforation elicits special considerations due to its blood-contaminated circumstances. It is known that conventional dental restorative materials are all leaking. Calcium sulfate is the material which react with water to become chemically set. This study, therefore, was performed to develop a new compound containing calcium sulfate and to evaluate its physical and biological characteristics. Three materials were used, IRM, calcium sulfate, calcium sulfate-hydroxyapatite compound. The composition of the calcium sulfate-hydroxyapatite compound was basically 50 % of calcium sulfate and 50 % of hydroxyapatite mixed with guajacol. The materials were mixed in conventional way and underwent four physical test procedures, setting time, solubility test, compressive strength, and marginal leakage test. All materials were evaluated under the scanning electron microscope to examine the marginal sealing ability. Animal experiment was also performed to test the materials' tissue response. Twenty-four dog's premolars were tested with either furcation perforations or apical retro-fillings. From the results, we found that calcium sulfate possess the good marginal sealing ability. However, calcium sulfate creates many voids which is caused by crystal thrusting action when it reacts with water. It seemed that the voids caused disintegration of the material which eventually lead to tissue reaction. By compounding calcium sulfate and hydroxyapatite, we were able to obtain the better physical properties but it showed larger marginal gap between the material and the root surface. Within the six weeks observation period, both IRM and calcium sulfate-hydroxyapatite compound showed good tissue responses in animal experiment. It is concluded that calcium sulfate would be the material of choice in root perforation repair, but the physical property needs to be further improved.

• 한국응용과학기술학회지
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• 제27권4호
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• pp.427-436
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• 2010

Much oyster shell is breeding by character and conduct of oyster-industry for a long time among them. An experimental study was carried out to investigate the recycling possibility of waste oyster shells, which induce environmental pollutions by piling up out at the open or the temporary reclamation. The purpose of this study is to develope eco-friendly binder using waste oyster shells, and to reinforce soils fur soft soil improvement. In this paper, a series of laboratory tests including compressive pot tests were performed to evaluate characteristics of soils treated by developed waste oyster shells with different water content of soils. Based on test results, eco-friendly Supporter manufactured from waste oyster shells were estimated as good resource materials for soft soil improvements. We got the conclusion by a series of experiment, It is verified that change of pH of soil is improved by mixing with oyster shells. The homogenization method for deducing apparent of oyster shells, which can consider micro-structure of mixed soil, is introduced. The improvement treatment leaded to enlarge fluctuation of soil moisture content. The effect of calcium concentration was good though improvement treatment of physical property. In addition, the crop yield in amelioration plots increased. It means that the increase of crop yield was caused by improvement of soil physical properties rather than improvement of calcium concentration.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.117-117
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• 2016

Total ankle replacement (TAR) is a visible option in the surgical treatment of degenerative or inflammatory diseases of ankle joint. it is attributed to the current TAR which has improvements in surgical technique, uncemented implant fixation and minimally constrained articulation. In the clinical result, they can show promised surgical result when compared to earlier attempts in TAR. However, TAR is still not as successful as total knee replacement (TKR) or total hip replacement (THR), it needs to be note that there are limitations in concerning of long term performance of TAR, the high failure rate still associated with wear of the PE (polyethylene) component that has related with their material property and surface roughness. The aim of this study was to introduce the tribology characteristics of total ankle joint prosthesis with one of TDR model which was fabricated to try multi-axis wear test as a region of motion in ankle joint. The wear specimen of TDR was prepared with Ti-6Al-4V alloy and UHMWPE (ultra-high molecular weight polyethylene) for tibia-talus and bearing component, respectively. A wear test was carried out using a Force 5 (AMTI, Massachusetts, US) wear simulator which can be allowed to move in three axis to flexion-extension ($+3^{\circ}{\sim}-6^{\circ}$), internal-external axial rotation (${\pm}5^{\circ}$), as well as sinusoidal compressive load (1.6 kN, R=10). All tests were performed following standard ISO 14243, wear rate was calculated with weight loss of UHMWPE bearing while the specimen has tested at certain cycles. As based on the preliminary results, wear rate of UHMWPE bearing was $7.9{\times}10^{-6}mg/cycles$ ($R^2=0.86$), calculated loss weight until $10^7cycles$ was 79 mg, respectively.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.725-728
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• 2008

본 연구에서는 고분말도 플라이애쉬를 사용한 콘크리트의 역학 및 수축특성을 분석하기 위하여 플라이애쉬의 분말도 4000, 6000, 8000급의 3수준과 치환율 30%로 설정 하였으며, 물-결합재비 40, 50%의 2수준으로 계획하였다. 또한, 고로슬래그 미분말 3종의 치환율 20%의 수준으로 3성분계의 조합조건을 설정하여 실험을 실시한 결과, 강도특성에서는 플라이애쉬의 분말도가 증가할수록 압축, 인장 및 휨 강도가 플레인 콘크리트와 동등하거나 상회하는 경향을 나타냄과 동시에 압축강도와 탄성계수의 관계에서도 플라이애쉬의 분말도가 증가할수록 탄성계수가 다소 증가하는 경향을 나타내었으며, 탄성계수는 장기재령으로 갈수록 확연히 증가하는 경향을 나타내었다. 또한, 건조수축에서는 플라이애쉬의 분말도에 대한 영향은 미미하였으나, 분말도가 증가할수록 감소하는 경향을 나타내었다.

• 한국건설순환자원학회논문집
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• 제3권3호
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• pp.244-251
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• 2015

본 연구는 대경권 지역에서 생산되는 부순모래를 콘크리트용 잔골재로 활용하기 위하여 물리적 특성 및 부순모래의 조립률과 치환률이 콘크리트의 특성에 미치는 영향을 검토하였다. 실험결과 천연사의 조립률이 2.0정도이고, 부순모래 조립률이 3.2이상인 경우 천연사와 부순모래의 합성입도를 만족시키기 위한 부순모래의 치환률은 50% 이하가 적당한 것으로 나타났다. 부순모래를 사용한 콘크리트는 부순모래의 치환률이 증가할수록 슬럼프는 증가하는 것으로 나타났으나, 부순모래의 치환률 75% 이상에서는 현저한 워커빌리티 저하현상을 나타내었다. 또한 부순모래를 사용한 콘크리트의 공기량 및 블리딩은 부순모래 치환률이 증가할수록 감소하였으며, 콘크리트 압축강도는 부순모래 조립률에 관계없이 시멘트페이스트와 골재간의 부착력 증진에 기인하여 치환률이 증가할수록 증가하는 경향을 나타내었다.

• 대한치과보철학회지
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• 제43권2호
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• pp.149-157
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• 2005

Statement of problem. Dental ceramics exhibit excellent esthetic property, compressive strength, chemical durability biocompatibility and translucency. However, it suffers from inherent brittle fractures. Various techniques and materials for intraoral porcelain repair has been suggested. Purpose. This study is to compare the tensile bond strength of four commonly used porcelain repair systems (Vivadent, Bisco, Ulttadent, Voco) and to insure the best system for the clinical application to the fractured porcelain. Materials and methods. A total of fifty specimens were fabricated. Specimens were stored in $37^{\circ}C$ distilled water for 7 days and thermocycling was performed(1000 cycles), and subjected to a tensile force parallel to the repair resin and porcelain interface by use of an Universal Testing Machine. Result. 1. Voco showed the highest tensile bond strength. In decreasing order, the tensile bond strength of the other materials was as follows : Ultradent, Bisco, Vivadent. 2. There was a statistically significant difference between the porcelain repair systems(Voco, Ultradent > Bisco, Yivadent) (p<0.05). 3. SEM examination of prepared porcelain surfaces revealed that the surface treated with Voco showed brittle fracture. However, Ultradent, Bisco and Vivadent showed ductile fracture. 4. All specimens treated with four porcelain repair systems showed adhesive failure between porcelain and composite resin.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.765-768
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• 2008

UHPC에서의 실리카 퓸은 강도와 유동성 증진에 있어 매우 중요한 요소라 할 수 있으며 그 사용량은 시멘트에 대해 25%이상(중량비)을 보편적으로 사용하고 있으나 실리카 퓸의 사용량에 따른 UHPC에 미치는 영향을 파악하는 노력들이 필요하다. 이에 본 연구에서는 실리카 흄의 사용량에 따른 유동성, 압축강도, 탄성계수, 휨강도의 역학적 특성과 SEM 및 MIP(Mercury Intrusion Porosimetry)를 통한 내부조직을 검토하였다. 검토결과, 적절한 실리카 퓸의 사용은 유동성과 강도를 증진시키는데 이는 포졸란 반응에 의한 수화물질의 증대와 필러역할에 의한 콘크리트 내부의 밀도가 효과적으로 증진되어 강도가 증가한 것을 MIP 실험을 통해 알 수 있었다. 또한 시멘트에 대해 중량비로 $10{\sim}25%$ 범위 내에서는 비슷한 역학적 특성을 나타내는 것으로 판단된다.