• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.83-87
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• 2002

Aerospace industries are widely using honeycomb sandwich structures that it has high specific strength and stiffness, chemical material resistance and fatigue resistance. But, in repairing process of damaged areas, one of the problems is that delamination can be occurred in the sound areas during and/or after the exposure to the elevated curing temperature in case that the repair process is repeated. Therefore, this study was conducted Flatwise tensile, Drum peel and Long beam flexural strength tests to evaluate the degree of degradation of mechanical properties of the honeycomb sandwich structures by affecting thermal aging. As the results, the decrease of mechanical strength was observed at the specific specimen which is exposed over 50hrs at $127^{\circ}C$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.715-718
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• 2000

We studied about electrical, chemical and mechanical characteristics of XLPE by dicumyl peroxide(DCP) and trimethylolpropane triacrylate(TMPTA) content ratio. DCP content was changed from 1.0 to 2.Sphr increasing 0.5phr. TMPTA content was changed 0.5 to 1.5phr increasing 0.5phr. Thermal analysis (DSC) was carried out in order to observe tendency of Tg according to DCP and TMPTA content. Tensile strength was measured in order to observe mechanical strength. In experimental results, content DCP 2.0phr and TMPTA 1.0phr has highest breakdown strength. Content DCP 2.0phr and TMPTA 0.5phr has lowest dielectric constant. Tendency of Tg did not affected by DCP and TMPTA content. Breakdown strength and Specific inductive capacity was measured.

• Steel and Composite Structures
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• 제19권3호
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• pp.585-599
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• 2015

This paper presents the experimental work on fatigue life and specific fatigue strength of circular hollow sectioned steel tube and wood filled circular hollow section steel tube. Burning effect was observed in the case of circular hollow sectioned steel tube when it is subjected to Maximum bending moment of 19613.30 N-mm at 4200 rpm, but this did not happen in the case of wood filled hollow section. Statistical analysis was done based on the experimental data and relations have been built to predict the number of cycles for the applied stress or vice versa. The relations built in this paper can safely be applied for design of the fatigue life or fatigue strength of circular hollow sections and wood filled hollow sections. Results were validated by static specific bending strengths determined by ANSYS using a known applied load.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.425-428
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• 2006

In order to estimate the reduction of laodbearing capacity, followed by the attributive change of heat while high strength concrete structure is revealed on fire it is necessary to evaluate, it is necessary to evaluate the property of material under high temperature such as thermal conductivity, specific heat, compressive strength, modulus of rigidity and diminution figure. Therefore, this study is for the purpose of presenting evaluation data for the analysis of thermal behavior about the high strength concrete material under high temperature, through the experiment by manufacturing concrete(40, 50, 60, 80, 100 MPa) commonly used in the construction field. As a result of the study, in the case of physical attribute, it demonstrates a greater fluctuation of change than the one of 30 MPa concrete. In case of specific heat, the high strength concrete, shown the serious diminution between $500{\sim}600^{\circ}C$, presents the thermal change area corresponding to the change of high strength concrete. In compressive strength, regardless of intensity of concrete, all of them show the first intensity loss between normal temperature and $100^{\circ}C$, the dramatic loss beyond $400^{\circ}C$. The concrete weighing above 50 MPa shows a twice lower dramatic intensity loss than the one weighing $30{\sim}40MPa$. The concrete ranging from $60{\sim}80MPa$, shows the biggest diminution of modulus of elasticity under $400^{\circ}C$, which implies the structural unstability of temperature.

• 한국안전학회지
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• 제30권3호
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• pp.7-12
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• 2015

CFRP composites are used as primary structural members in various industrial fields because their specific strength and specific stiffness are excellent in comparison to conventional metals. Their usage is expanding to high added-value industrial fields because they are more than 50% lighter than metals, and have excellent heat resistance and wear resistance. However, when CFRP composites suffer impact damage, destruction of fiber and interface delamination occur. This causes an unexpected deterioration of strength, and for this reason it is very difficult to ensure the reliability of the excellent mechanical properties. Therefore, for the destruction mechanism in bending with impact damage, this study investigated the reinforcement data regarding various external loads by identifying the consequential strength deterioration. Specimens were damaged by impact with a steel ball propelled by air pressure. Decrease in bending strength caused by the tension and compression of the impact side, and depending on the lamination direction of fiber and interface inside the specimen. From the bending test it was found that the bending strength reduced when the impact energy increased. Especially in the case of compression on the impact side, as tensile stress occurred at the damage starting point, causing rapid failure and a substantially reduced failure strength.

• Journal of the Korean Wood Science and Technology
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• 제34권2호
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• pp.1-9
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• 2006

The structural wooden members of the ancient building are deteriorated by fungi and termite over time. The deteriorate of the members causes the decrease of the specific gravity and the strength of it, so the stability of the building is threatened. Therefore, in this study, the evaluation of the specific gravity, which is correlated with the strength of the wood, was conducted in the post member using Nondestructive Evaluation (NDE) - Drilling Resistance Test (DRT). For the purpose of it, the specific gravity and drilling resistance of small specimens was measured to obtain the correlation between the specific gravity and the drilling resistance. And then, the drilling resistance test of the post members, which were expected to have the deteriorated parts, was performed. Consequently, the correlation between the specific gravity and the drilling resistance was very high ($R^2=0.89$) and the distributions of the specific gravity were evaluated for the each member. Also, the results were verified by the visual inspection of the cross section of it. Especially, the various variations of the wood member such as the deteriorated parts with termite or fungi and the crack could be detected exactly but the knot couldn't because the drill could pass by or could not penetrate the knot.

• Restorative Dentistry and Endodontics
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• 제40권1호
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• pp.23-29
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• 2015

Objectives: The aim of this study was to evaluate the effect of pre-etching on the bond strength of silorane-based composite specific adhesive system to dentin. Materials and Methods: Thirty human molars were randomly divided into 5 groups according to the different bonding strategies. For teeth restored with silorane-based composite (Filtek Silorane, 3M ESPE), the specific self-etching adhesive system (Adhesive System P90, 3M ESPE) was used with and without pre-etching (Pre-etching/Silorane and Silorane groups). Teeth restored with methacrylate based-composite (Filtek Z250, 3M ESPE) were hybridized with the two-step self-etching system (Clearfil SE Bond, Kuraray), with and without pre-etching (Pre-etching/Methacrylate and Methacrylate groups), or three-step adhesive system (Adper Scotchbond Multi-Purpose, 3M ESPE) (Three-step/Methacrylate group) (n = 6). The restored teeth were sectioned into stick-shaped test specimens ($1.0{\times}1.0mm$), and coupled to a universal test machine (0.5 mm/min) to perform microtensile testing. Results: Pre-etching/Methacrylate group presented the highest bond strength values, with significant difference from Silorane and Three-step/Methacrylate groups (p < 0.05). However, it was not significantly different from Pre-etching/Silorane and Methacrylate groups. Conclusions: Pre-etching increased bond strength of silorane-based composite specific adhesive system to dentin.

• Journal of the Korean Wood Science and Technology
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• 제39권3호
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• pp.252-257
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• 2011

국내에서 생산되는 목재에 대한 나사못 유지력을 기존의 식으로부터 수정된 예측 식으로 나타내기 위해 나사 못 뽑기 실험을 실시했다. 본 연구에 사용된 나사못은 No. 6, No. 8 및 No. 10이었다. 예측 식은 길이가 서로 다른 No. 8 나사못의 실험결과와 매우 일치하였다. 나사못 유지력의 예측 식은 나사못의 직경과 관입길이 및 목재비중의 함수로 나타냈다. 예측 식은 나사못 길이가 25와 30 mm에서 5% 이내로 작게 예측되었으나 18과 38 mm에서 큰 값을 보였다.

• 지질공학
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• 제13권3호
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• pp.335-344
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• 2003

본 연구에서는 전라남도 장성과 화순에 분포하는 석회암풍화토의 물성 및 전단 특성을 연구하였다. 석회암풍화토의 교란시료에 대한 물성 및 전단 특성을 파악하기 위하여 실내 시험이 수행되었다. 연구지역의 석회암풍화토에 대한 물성 및 전단 특성은 다음과 같다 비중(Gs)은 2.78~2.80, 액성한계(LL)는 37~38(%), 소성지수(PI)는 13.7~15.4이며 흙의 분류(USCS)는 CL에 해당된다. 불포화 시료의 직접전단시험 (vd, $1.5t/\textrm{m}^3$)에 의한 강도정수는 점착력(c)이 3.07~4.4 ($t/\textrm{m}^2$) 그리고 내부마찰각($\Phi$)은 $34.8~42.4^{\circ}$의 범위를 보인다. 화강암풍화토 (양, 1997; 문. 1998; 박, 1998)와 비교해 보면, 연구지역의 석회암 풍화토의 물리적 특성은 일반적으로 차이를 보이며, 전단 강도정수 중, 내부마찰각은 대체적으로 유사한 경향을 보이는 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.73-76
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• 1999

In recent, concrete material like specific cement and additives having many functions hsa been developed. In road pavement, ultra high early strength cement or organic material are used to open the road early, but there are many restrictions like workable time and special equipment. We aim to developed specific concrete which 1 day strength is over 300kgf/$\textrm{cm}^2$ to open the road within one day and workable time is maintained over 1 hour that can make the concrete ready mixed concrete. In this study, we are convinced if the ratio of hauyne clinker or its additive is increased early strength property is progressed and if the ratio of non hydrous gypsum is increased longtime strength is progressed. The concrete strength is 290-310 kgf/$\textrm{cm}^2$ at 1 day, 570-640 kgf/$\textrm{cm}^2$ at 28 day and the workable time is maintained over 30 minutes. As the results of this experiments We find out the possibility to developed the 1 day usable ready mixed concrete with high early strength.