• 비파괴검사학회지
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• 제15권2호
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• pp.357-363
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• 1995

CFRP 복합 재료를 접착 접합한 single-lap 및 double-lap 접합 시험편의 disbond 크기를 초음파 C-scan 및 simulated stress wave를 이용하여 정량적으로 평가하고자 하였다. 초음파 C-scan 시험을 통해 인공 결함의 크기가 확인된 시험편을 사용하여, 접합부를 통과한 응력파의 주파수를 변화시키면서 peak amplitude를 측정하여 주파수 응답성을 구하였으며, 이를 분석한 결과 두 적층판의 두께 방향 기본 공진 및 3차 공진 주파수에서 peak amplitude가 극값을 보이며, 접합 면적에 비례함을 관측할 수 있었다. 이 결과로 표준시험편만 준비된다면 결함의 정량적 평가 및 현장 적용에도 이용할 수 있을 것으로 기대된다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 춘계 학술발표회 논문집
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• pp.250-257
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• 2002

Pseudo dynamic test is an on-line computer control method to achieve the realism of shaking table test with the economy and versatility of the conventional quasi-static approach Pseudo dynamic tests of six full-size RC bridge piers have been carried out to investigate their seismic performance. For the purpose of precise evaluation, the experimental investigation was conducted to study the seismic performance of the real size specimen, which is constructed for highway bridge piers in Korean peninsula. Since it is believed that Korea belongs to the moderate seismicity region, five test specimens were designed in accordance with limited ductility design concept. Another one test specimen was nonseismically designed according to a conventional code. Important test parameters were transverse reinforcement and lap splicing. Lap splicing was frequently used in the plastic hinge region of many bridge columns. Furthermore, the seismic design code is not present about lap splice in Korean Roadway Bridge Design Code. The results show that specimens designed according to the limited ductility design concept exhibit higher seismic resistance. Specimens with longitudinal steel lap splice in the plastic hinge region appeared to significantly fail at low ductility level.

• Korean Chemical Engineering Research
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• 제55권5호
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• pp.623-628
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• 2017

화력발전소의 연료로 사용되는 우드펠릿을 시료로 하여 시료 용기의 크기에 따른 최소자연발화온도를 구하였으며, 이 온도로부터 Frank-Kamenetskii의 열발화 이론을 이용하여 겉보기 활성화 에너지를 구함으로써 물질의 위험성을 예측하였다. 용기의 크기가 클수록 발화한계온도는 낮아졌으며, 겉보기 활성화 에너지는 37.83 kcal/mol을 구하였다. 또한 시료의 용기가 커질수록 발화유도시간 및 최고온도에 도달하는 시간이 길어졌다.

• 한국의류학회지
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• 제12권3호
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• pp.343-350
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• 1988

This study was carried out to investigate the microstructure and physical property of PET POY which was taut-annealed under various conditions. The DSC melting curves of annealed PET POY showed double melting peaks in most cases. As temperature and time increased, form II crystal became sharp and increased in size, and form I crystal decreased in size. The slower the heating rate, the higher the programmed heating effect during DSC analysis. Crystallinity and briefringence of annealed specimens increased as the treatment temperature and time increased. Breaking tenacity of specimens treated for 3 minutes increased as the treatment temperature increased, but others decreased. Elongation at break decreased as the annealing temperature and time increased. Dye uptake of annealed specimens decreased as the temperature increased up to $190^{\circ}C\~210^{\circ}C$. then the uptakes increased at higher temperatures. At the same temperature, dye uptake of the specimen decreased as time increased.

• 콘크리트학회논문집
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• 제17권5호
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• pp.829-834
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• 2005

A series of reinforced G109 type specimens was fabricated and pended with a 15 weight percent NaCl solution. Mix design variables included 1) two cement alkalinities (equivalent alkalinities of 0.32 and 1.08), 2) w/c 0.50 and 3) two rebar surface conditions (as-received and wire-brushed). Potential and macro-cell current between top and bottom bars were monitored to determine corrosion initiation time. Once corrosion was initiated, the specimen was ultimately autopsied to perform visual inspection, and the procedure included determination of the number and size of air voids along the top half of the upper steel surface. This size determination was based upon a diameter measurement assuming the air voids to be half spheres or ellipse. The followings were reached based upon the visual inspection of G109 specimens that were autopsied to date. First, voids at the steel-concrete interface facilitated passive film breakdown and onset of localized corrosion. Based upon this, the initiation mechanism probably involved a concentration cell with contiguous concrete coated and bare steel serving as cathodes and anodes, respectively. Second, the corrosion tended to initiate at relatively large voids. Third, specimens with wire-brushed steel had a lower number of voids at the interface for both cement alkalinities, suggesting that air voids preferentially formed on the rough as-received surface compared to the smooth wire brushed one.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.885-890
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• 2002

Pseudo dynamic test is an on-line computer control method to achieve the realism of shaking table test with the economy and versatility of the conventional quasi-static approach. Pseudo dynamic tests of four full-size RC bridge piers have been carried out to investigate their seismic performance. For the purpose of precise evaluation, the experimental investigation was conducted to study the seismic performance of the real size specimen, which is constructed for highway bridge piers in Korean peninsula. Since it is believed that Korea belongs to the moderate seismicity region, three test specimens were designed in accordance with limited ductility design concept. Another one test specimen was nonseismically designed according to a conventional code. Important test parameters were transverse reinforcement and lap splicing. Lap splicing was frequently used in the plastic hinge region of many bridge columns. Furthermore, the seismic design code is not present about lap splice in Korean Roadway Bridge Design Code. The results show that specimens designed according to the limited ductility design concept exhibit higher seismic resistance. Specimens with longitudinal steel lap splice in the plastic hinge region appeared to significantly fail at low ductility level.

• International Journal of Concrete Structures and Materials
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• 제9권3호
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• pp.295-306
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• 2015

Simulating natural leaching process for cementitious materials is essential to perform long-term safety assessments of repositories for nuclear waste. However, the current test methods in literature are time consuming, limited to crushed material and often produce small size samples which are not suitable for further testing. This paper presents the results from the study of the physical (gas permeability as well as chloride diffusion coefficient) and mechanical properties (tensile and compressive strength and elastic modulus) of solid cementitious specimens which have been depleted in calcium by the use of a newly developed method for accelerated calcium leaching of solid specimens of flexible size. The results show that up to 4 times increase in capillary water absorption, 10 times higher gas permeability and at least 3 times higher chloride diffusion rate, is expected due to complete leaching of the Portlandite. This coincides with a 70 % decrease in mechanical strength and more than 40 % decrease in elastic modulus.

• 대한기계학회논문집A
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• 제33권4호
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• pp.409-416
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• 2009

Standard procedures for a fracture toughness testing require very severe restrictions for the specimen geometry to eliminate a size effect on the measured properties. Therefore, the used standard fracture toughness data results in the integrity assessment being irrationally conservative. However, a realistic fracture in general structures, such as in nuclear power plants, may develop under the low constraint condition of a large scale yielding with a shallow surface crack. In this paper, cleavage fracture toughness tests have been made on side-grooved PCVN (precracked charpy V-notch) type specimens (10 by 10 by 55 mm) with various crack depths. The constraint effects on the crack depth ratios were evaluated quantitatively by the developed scaling method using the 3-D finite element method. After the fracture toughness correction from scaling model, the statistical size effects were also corrected according to the standard ASTM E 1921 procedure. The results were evaluated through a comparison with the $T_0$ of the standard CT specimen. The corrected $T_0$ for all of the PCVN specimens showed a good agreement to within $5.4^{\circ}C$ regardless of the crack depth, while the averaged PCVN $T_0$ was $13.4^{\circ}C$ higher than the real CT test results.

• Structural Engineering and Mechanics
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• 제61권5호
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• pp.637-643
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• 2017

Carbon fiber reinforced polymers (CFRPs) have been recently investigated as an alternative material for Geosynthetics to improve soil properties. One of the factors influencing the fiber orientation and mechanical properties of CFRP is the effect of soil overburden pressure. This study investigates the tensile behavior of cast-in-place CFRP. During the curing time of specimens, a wide range of normal stress is applied on specimens sandwiched between the soils. Two different soil types are used to determine the effect of soil grain size on the mechanical properties of CFRP. Specimens are also prepared with different specifications such as curing time and mixing soil in to the epoxy. In this study, tensile tests are conducted to investigate the effect of such parameters on tensile behavior of CFRP. The experimental results indicate that by increasing the normal stress and soil grain size, the ultimate tensile strength and the corresponding strain of CFRP decrease; however, reduction in elastic modulus is not noticeable. It should be noted that, increasing the curing period of epoxy resin and mixing soil in to the epoxy have no significant effect on the tensile properties of CFRP.

• 한국재료학회지
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• 제13권6호
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• pp.365-368
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• 2003

Small amounts of additives such as mol % 0.13 NiO and mol % 0.01 $CaCO_3$were added to Cu-Zn-Mg ferrites. Basic composition of the Cu-Zn-Mg ferrites was $Cu_{Cu}$X/$Fe_{0.054}$ /$Zn_{0.486}$$Mg_{0.407}$ $Fe_{1.946}$ $O_4$(group A) and $Cu_{0.263}$$Fe_{0.027}$ $Zn_{0.503}$ $Mg_{0.262}$ $Fe_{1.973}$ $O_4$(group B). Specimens were sintered at different temperatures (1010, 1030, $1050^{\circ}C$) for 2 hours in air followed by an air cooling. Then, effects of various composition and sintering temperatures on the microstructure and the magnetic properties such as inductions, coercive forces, and initial permeabilities of the Cu-Zn-Mg ferrites were investigated. The average grain size increased with the increase of sintering temperature. The magnetic properties obtained from the aforementioned Cu-Zn-Mg ferrite specimens were 1,724 gauss for the maximum induction, 1.0 oersted for the coercive force, and 802 for the initial permeability. These magnetic properties indicated that the specimens could be utilized as the core of IFT (intermediate frequency transformer) and antenna in the amplitude modulation.