• 한국건축시공학회지
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• 제14권4호
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• pp.336-342
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• 2014

전단보강근이 없는 고강도 콘크리트 보의 전단능력을 평가하기 위하여 전단경간비 2.4인 시험체를 콘크리트 압축강도 60MPa 이상의 4단계별로 제작하여 파괴하중과 전단응력을 기존의 국내외 설계기준과 비교하였다. 특히 적용가능한 한계콘크리트 압축강도 70MPa 이상인 경우 전단응력을 기존 제안식을 보정하지 않고 적용하여 실험결과와 비교하였다. 고강도 콘크리트 보의 전단파괴 강도를 결정하여 기존의 설계기준결과와 차이를 분석하고 시공현장에서 고려해야할 특기사항을 제안하고자 한다.

• 비파괴검사학회지
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• 제28권2호
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• pp.125-130
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• 2008

레이저 용접부의 국소 잔류응력을 측정하기 위한 비파괴 기법으로 구형압입시험이 제안되었다. 용접상태 절단휠의 구형압입시험으로 얻어진 겉보기 항복강도와 절단횔 용접부에 대한 응력완화 열처리 이후 동등한 위치에서 구한 고유 항복강도를 정량적으로 비교하였다. 고유항복강도가 탄성한도 내의 잔류응력에 의해서 변화하지 않는다고 고려하면 용융선으로부터 거리에 따른 두 항복강도의 차이가 용접잔류응력의 분포로 나타난다. 레이저 용접된 다이아몬드 절단휠의 구형압입시험으로부터 약 10 mm 폭에 걸친 잔류응력의 분포를 확인하였으며, 잔류응력은 쌩크와 절단팁 내에서 각각 최대 압축 및 인장 잔류응력치를 나타내었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.405-408
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• 2008

PSC 거더의 단면 개선과 장경간화를 위한 주요 영향 요소는 단면 형상과 콘크리트 강도이며, 이중 콘크리트의 강도에 의한 영향은 거더의 휨강도 증가보다는 거더 상하연의 허용인장강도 증가에 크게 기여한다. 본 연구에서는 60MPa급 고강도 PSC를 논산-전주간 고속도로 확장공사 1공구 원수교의 거더에 시험 시공하였고, 논산방향 4차선에 35m 단경간 IPC 거더 8본에 타설하였다. 거더 콘크리트 타설 기간 중 지속적인 표면수 관리와 생산시 에어미터법을 사용하여 단위수량을 보정하여 고강도 콘크리트의 품질관리를 실시하였다. 현장 거더 콘크리트의 압축강도는 목표 강도를 안정적으로 확보함을 확인하였고, 거더 콘크리트의 수화열을 측정하였다. 하지만 동일재료와 시공방법을 사용하였음에도 강도의 편차가 다소 크게 나타나 향후 고강도 콘크리트를 현장에서 타설하여 적용할 경우 이에 대한 대책을 반드시 마련해야 할 것으로 판단된다.

• Computers and Concrete
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• 제21권3호
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• pp.261-267
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• 2018

This paper discusses a study of cement mortar reinforced with Graphene Oxide (GO) flakes carried out at the University of Plymouth. Over 60 specimens were prepared and tested to obtain the tensile, compressive and flexural strengths of cement mortar with/without 0.5% GO flakes by weight of cement. The dispersion of the GO flakes and the effect of the use of polycarboxylate ether superplasticizer (0.2% by weight of cement) on the material strength are discussed. Images of the particle sizes of GO are presented from the transmission electron microscopy analysis. In addition, the images from the field emission scanning electron microscope analysis are also presented to show the difference of the microscopic structure of cement mortar with/without GO. The results of the strength tests are presented. It is shown that the inclusion of the GO flakes in general led to positive results, which suggest that GO improved the tensile, compressive and flexural strengths of cement mortar.

• 한국정보교육학회:학술대회논문집
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• 한국정보교육학회 2011년도 동계학술대회
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• pp.153-158
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• 2011

최근 교육현장에서 학습에 모바일을 사용하고자 하는 아이디어는 모바일의 이동성, 현장성, 휴대성, 시성, 학습정보 접근의 용이성이라는 장점에서부터 시작된다. 특히 안드로이드폰에서 구글맵 API와 GPS를 기반으로 현재 위치의 정보(지리 및 문화관련 사진과 텍스트 등)를 공유할 수 있는 본 연구의 애플리케이션은 이러한 장점들을 적극적으로 활용한 것이며 교실밖에서, 또 정규수업 이후에도 활용할 수 있어서 지속적인 학습 자원의 관리와 자기 주도적 학습의 가능성을 열어두고 있기에 더욱 효과적이라고 할 수 있다.

• Toxicological Research
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• 제17권4호
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• pp.279-286
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• 2001

Recently, there is an increasing nationwide concern in Korea that exposure to electric and magnetic fields in the home environment may not be safe in humans. To identify possible effects of horizontally polarized magnetic fields (MF) exposure on embryo-fetal development, timed-mated female Sprague-Dawley rats (24/group) received continuous exposure to 60 Hz MF at field strengths of 0 Gauss (sham control), 50mG,833 mG, or 5000 mG. Dams received MF of sham exposures for 22hr/day on gestation days 6 through 20. Experimentally generated MF were monitored continuously througout the study. There was no evidence of maternal toxicity of developmental toxicity in any MF-exposed groups. Mean maternal body weight, organ weights, and gross findings in groups exposed to MF did not differ from those in sham control. No significant differences in fetal deaths, fetal body weight, and placental weight were observed between MF-exposed groups and sham control. External, visceral, and skeletal examination of fetuses demonstrated no significant differences in the incidence of fetal malformations between MF-exposed and sham control groups. In conclusion, exposure of pregnant Sprague-Dawley rats to 60 Hz at MF strengths up to 5000 mG during gestation day 6-20 did not produce any biologically significant effect in either dams of fetuses.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.318-321
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• 2000

Most compressive strengths commonly used in the construction field are in a range of 240 to 300 kgf/$\textrm{cm}^2$ at 28 days. To get this rage of strengths, however, high-flowing concrete requires cementitious binders more than 400 to 450 kg/$\textrm{cm}^2$ for preventing segregation and sedimentation of aggregates. This amount of cementitious binder generates a large emission of excessive hydration heat, which may consequently induce harmful cracks in concrete structure. In order to reduce excessive hydration heat, thus, this paper aims at fabricating a high-flowing concrete under the condition that cement content is kept as low as 350kg/$\textrm{cm}^3$ by using viscose agents. In a parametric study, effects of cement types such as a ternary blended cement and Type V on he physical characteristics of high-flowing concrete were evaluated. In addition, the influence of viscosity was also investigated by applying two different viscose agents, one in a range of 6,000 to 10,000 cps and the others of 10,000 to 14,000 cps. In terms of chemical admixtures used in concrete mixture, the superplasticizer was Sulfonated Melamine-Formaldehyde Condensate with about 30,000 of molecular weight, and main component of viscose agent was HPMC (Hydroxy Propyl Methyl Cellulose). Slump flow was fixed at 50cm with different dosages of superplasticizer in weight.

• Elastomers and Composites
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• 제53권4호
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• pp.202-206
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• 2018

Five solution styrene butadiene rubber/neodymium butadiene rubber (SSBR/NdBR) composites were manufactured using different ratios of SSBR and NdBR. In this study, the composites were reinforced with NdBR and silica to confirm the physical properties of SSBR used for treads of automobile tires and the dispersibility with silica. The morphologies of the rubber composites were observed using field-emission scanning electron microscopy (FE-SEM). The crosslinking behaviors of the composites were tested using a rubber process analyzer (RPA), and the abrasion resistances were tested using a National Bureau of Standards (NBS) abrasion tester. The hardness values, tensile strengths, and cold resistances of the composites were also tested according to ASTM standards. Increased NdBR content yielded composites with excellent crosslinking properties, abrasion resistances, hardnesses, tensile strengths, and cold resistances. The crosslinking point increased due to the double bond in NdBR, thereby increasing the degree of crosslinking in the composites. The NdBR-reinforced composites exhibited excellent abrasion resistances, which is explained as follows. In SSBR, a breakage is permanent because a resonance structure between styrene and SSBR forms when the molecular backbone is broken during the abrasion process. However, NdBR forms an additional crosslink due to the breakdown of the molecular backbone and high reactivity of the radicals produced. In addition, the low glass transition temperature (Tg) of NdBR provided the rubber composites with excellent cold resistances.

• International Journal of Reliability and Applications
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• 제7권1호
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• pp.27-39
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• 2006

Many real world cases in material failure analysis do not follow perfectly the normal distribution. Forcing of the normality assumption may lead to inaccurate predictions and poor product quality. We examine the failure process of the internal bond (IB or tensile strength) of medium density fiberboard (MDF). We propose a forced censoring technique that closer fits the lower tails of strength distributions and better estimates extremely smaller percentiles, which may be valuable to continuous quality improvement initiatives. Further analyses are performed to build an accelerated common-shaped Weibull model for different product types using the $JMP^{(R)}$ Survival and Reliability platform. In this paper, a forced censoring technique is implemented for the first time as a software module, using $JMP^{(R)}$ Scripting Language (JSL) to expedite data processing, which is crucial for real-time manufacturing settings. Also, we use JSL to automate the task of fitting an accelerated Weibull model and testing model homogeneity in the shape parameter. Finally, a package script is written to readily provide field engineers customized reporting for model visualization, parameter estimation, and percentile forecasting. Our approach may be more accurate for product conformance evaluation, plus help reduce the cost of destructive testing and data management due to reduced frequency of testing. It may also be valuable for preventing field failure and improved product safety even when destructive testing is not reduced by yielding higher precision intervals at the same confidence level.

• 한국전자파학회논문지
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• 제22권1호
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• pp.1-8
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• 2011

본 논문에서는 전자파 장해 측정용 야외시험장과 전자파 내성 시험장인 GTEM 셀과의 상관계수를 이용하여 GTEM 셀에서 전자파 허용 기준을 제시하였다. 실험적인 상관계수를 도출하기 위해서 피시험 기기를 제작하였으며, 제작된 피시험 기기의 전기장 세기를 10 m 야외시험장과 GTEM 셀에서 측정하였다. 또한, GTEM 셀의 3방위법을 역변환함으로써 GTEM 셀에서 복사 전력에 대한 허용 기준을 도출하였다. GTEM 셀의 3방위법과 15방위법에 대한 이론치를 프로그램화 하였으며, 프로그램을 통한 결과 값과 시험장에서 측정한 값을 비교 분석하였다. GTEM 셀에서 전자파 허용 기준을 새롭게 제시함으로써 GTEM 셀이 야외시험장의 전자파 방사(EMI) 대체 시험장으로서 활용될 수 있음을 확인하였다.