• Advanced Composite Materials
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• 제16권2호
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• pp.83-94
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• 2007

Woven sisal textile fiber reinforced composites were used to evaluate fracture toughness, tensile and three-point bending. The water absorption testing of all specimens was repeated five times in this study. All specimens were immersed in pure water during 9 days at room temperature, and dried in 1 day at $50^{\circ}C$. Two kinds of polymer matrices such as epoxy and vinyl-ester were used. Fractured surfaces were taken to study the failure mechanism and fiber/matrix interfacial adhesion. It is shown that it can be enhanced to improve their mechanical performance to reveal the relationship between fracture toughness and water absorption fatigue according to different polymer matrices. Water uptake of the epoxy composites was found to increase with cycle times. Mechanical properties are dramatically affected by the water absorption cycles. Water-absorbed samples showed poor mechanical properties, such as lower values of maximum strength and extreme elongation. The $K_{IC}$ values demonstrated a decrease in inclination with increasing cyclic times of wetting and drying for the epoxy and vinyl-ester.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.729-736
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• 2022

Earth is facing a serious problem of pollution and scarcity of energy sources. The synthetic fibers used in automobile and Aerospace manufacturing sectors are non-renewable and harmful to environment. International Agency such as FAA and SAE is forcing for green fuel, green materials and structures. Further exploration is much needed to understand its potential in structural applications. In the current study, hemp and Jute fibre based composites were developed and tested for assessing their suitability for possible applications in automobile and aerospace sectors. Composites were undergone tensile test, water absorption test, and fatigue analysis to understand its behavior under various loading conditions. The finite element analysis has been carried out to understand the fatigue behaviour of composites. The results revealed that the usage of hemp and jute fibre reinforced composites can improve mechanical properties and have shown a viable alternative to replace synthetic fibres such as glass fibres for specific applications. Hemp reinforced bio-composites have shown better performance as compared to Jute reinforced bio-composites while water resistance characteristics for hemp is poorer to jute fibres.

• 한국재료학회지
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• 제3권1호
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• pp.84-94
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• 1993

GFRP복합재료의 피로거동은 하중형식, 재질 및 섬유의 강화구조, 환경적인 인자들의 영향을 크게 받는것으로 알려져 있다. 본 연구에서는GFRP의 피로거동에 미치는 증류수 흡습의 영향을 알아보기 위해 chopped strand glass mat강화 불포화 polyester수지 복합재료의피로특성을 조사하였다. 피로균열은 건조재와 흡습재 모두 피로 cycle초기에 발생하며 그 후 균열성장이 점차 둔화되는 영역과 가속되는 영역으로 나뉘어졌다. 또한 증류수의 흡습은 섬유와 기지재 사이의 결합력을 저하시키며 그로 인해 균영성장방향에 수직인곳에서의 fiber pull-out 발생과 균열성장방향에 있는 섬유들에서의 debonding이 증가하여 피로강도가 저하하였다.

• Composites Research
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• 제26권5호
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• pp.328-333
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• 2013

본 연구에서는 유리섬유/폴리프로필렌 복합재료 고정판을 인조골에 체결하여 실제 골절치료 시술 상황을 모사하였으며, 고정판의 적합성을 판단하기 위하여 수분 흡수율, 스크류의 체결 상태, 하중 조건의 변화에 따른 피로 실험을 진행하였다. 실험 결과 0~12주 동안 수분 흡수가 이루어진 모든 시편에서 기대 수명인 65만 사이클을 넘는 100만 사이클 이상의 피로 수명을 가짐을 확인하였다. 스크류 체결 상태는 골절부의 변형률 차이에 주목할만한 영향을 미치지 못하였다. 본 논문에서는 유리섬유/폴리프로필렌 복합재료 고정판을 다양한 환경조건 하에서 압축-압축 피로실험을 수행하여 기계적 우수성을 입증하였으며, 이 결과는 향후 금속 고정판을 복합재료 고정판으로 대체하기 위한 관련 연구에 유용한 정보를 제공할 것으로 기대된다.

• Journal of Pharmaceutical Investigation
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• 제25권1호
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• pp.1-7
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• 1995

After oral administration of various drinking solutions, the initial absorption rate of water through gastrointestinal tract of the rabbits was evaluated using tritinated water $(^3H_2O)$ as a marker to develop the sports drinking beverage for Korean people. The polynomial curve fitting over 20 min was performed using computer program to obtain the initial absorption rate of water from the tangent line of the fitted equation because initial absorption rate of water was more critical compared to elimination rate during exercise. The amount of water absorbed was increased but a large variation was observed among testing preparations in a small study group $(2{\leq}n{\leq}6)$. The initial absorption rate of water from isotonic sports drinking beverages was statistically significant when compared to hypertonic cola but was not significant when compared to hypotonic solutions (potable water and barley water). In case of hypertonic sports dringking beverages (i.e. Takeda), initial absorption rate of water was not improved and efficient when compared to other isotonic sports dringking beverages. The initial absorption rate of water from prescribed isotonic sample solution containing electrolytes, carbohydrates, and vitamins was not statistically significant when compared to other isotonic drinking beverages but showed similar absorption profile. It was obvious that isotonic solutions simultaneously containing electrolytes, vitamins and carbohydrates (sugar and glucose) had a tendency to increase the initial absorption of water compared to hypotonic (potable water and barley water) and hypertonic preparations (orange juice and cola). Although statistical significance of initial absorption rate of water between isotonic sports drinking beverages and hypotonic potable and barley water was not observed, unlike the hypertonic solutions, isotonic sports drinking beverages may aid not only to replenish loss of water, electrolytes and other nutrients during the exercise but also to prevent dehydration and muscle fatigue, resulting in improved physical performance in an exhausted condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3059-3066
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• 2008

It is reported that the life of generator stator windings is expected about 30 years and a leak and water absorption phenomena can be progressed by fatigue, vibration, and corrosion. The water-cooled generator stator windings which were operated over 15 years are over 20 units and the mechanical problems such as leak and water absorption were found in the generator stator windings. In this paper, the systematic mechanical integrity evaluation methods which are applied to the water-cooled generator stator windings within the country are introduced.

• Journal of Advanced Marine Engineering and Technology
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• 제17권2호
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• pp.52-59
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• 1993

This study is investigated of tensile and fatigue strength for advanced composite materials under hygrothermal environment. The materials used are two types of Carbon/Epoxy reinforced composite materials i.e., 13$0^{\circ}C$ cure-type composite T-1/347, and 18$0^{\circ}C$ cure-type MM-1/982X. These are composed by cross-ply laminates. Test condition is the distilled water of 8$0^{\circ}C$. The separate absorption contents estimated by the Fick's diffusion rule are similar to the experiment results. The tensile strength of T-1/347 wet specimens more increased than that of dry ones, but that of MM-1/982X decreased. The fatigue strengthes of both T-1/347 and MM-1/982X wet specimen more decreased than those of dry specimens.

• 대한기계학회논문집A
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• 제30권7호
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• pp.779-786
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• 2006

Woven sisal textile reinforced composites were manufactured to evaluate fracture toughness, and tensile test. All specimens were immersed in water five times. All specimens are immersed in pure water during 9 days at room temperature, and dried in 1 day at $50^{\circ}C$. Two kinds of polymer matrices such as epoxy and vinyl-ester were used. Fractured surface were investigated to study the failure mechanism and fiber/matrix interfacial adhesion. It is shows that it can be enhanced to improve their mechanical performance to reveal the relationship between fracture toughness and water absorption fatigue according to different polymer matrices. Water uptake of the epoxy composites was found to increase with cycle times. Mechanical properties are dramatically affected by the water absorption cycles. Water-absorbed samples observed poor mechanical properties such as lower values of maximum strength and extreme elongation. The $K_{IC}$ values demonstrate a decrease in inclination with increasing cyclic times of wetting and drying fur the epoxy and vinyl-ester.

• 대한치과교정학회지
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• 제45권5호
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• pp.268-272
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• 2015

Clear thermoplastic retainers have been widely used in daily orthodontics; however, they have inherent limitations associated with thermoplastic polymer materials such as dimensional instability, low strength, and poor wear resistance. To solve these problems, we developed a new type of clear orthodontic retainer that incorporates multi-layer hybrid materials. It consists of three layers; an outer polyethylenterephthalate glycol modified (PETG) hard-type polymer, a middle thermoplastic polyurethane (TPU) soft-type polymer, and an inner reinforced resin core. The resin core improves wear resistance and mechanical strength, which prevent unwanted distortion of the bucco-palatal wall of the retainer. The TPU layer absorbs impact and the PETG layer has good formability, optical qualities, fatigue resistance, and dimensional stability, which contributes to increased support from the mandibular dentition, and helps maintain the archform. This new type of vacuum-formed retainer showed improved mechanical strength and rate of water absorption.

• Advances in concrete construction
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• 제4권2호
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• pp.123-143
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• 2016

Use of heavy fuel fly ash (HFFA) (diesel and cracked fuel) for power generation in Saudi Arabia has generated and accumulated large quantities of HFFA as a byproduct. In this research, HFFA is studied with the emphasis on the utilization of this waste material in concrete blocks and asphalt concrete mixes. Two types of mixes, one with low and other with high cement content, were studied for concrete blocks. Different mixes having varying percentages of HFFA (0% to 25%), as cement/sand replacement or as an additive, were studied. The performance of concrete blocks is evaluated in terms of compressive strength, water absorption, durability and environmental concerns. The results showed that blocks cannot be cast if more than 15% HFFA is used; also there is a marginal reduction in the strength of all the mixes before and after being exposed to the sulfate solution for a period of ten months. HFFA is studied in asphalt concrete mixes in two ways, as an asphalt modifier (3&5%) and as a filler (50%) replacement, the results showed an improvement in stiffness and fatigue life of mixes. However, the stability and indirect tensile strength loss were found to be high as compared to the control mix due to moisture damage, indicating a need of using antistripping agents. On environmental concerns, it was found that most of the concerned elements are within acceptable limits also it is observed that lower concentration of barium is leached out with the higher HFFA concentrations, which indicates that HFFA may work as an adsorbent for this leaching element.