• Structural Engineering and Mechanics
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• 제34권2호
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• pp.175-188
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• 2010

This paper deals with the buckling and postbuckling responses, and the progressive failure of square laminates of symmetric lay-up with a central rectangular cutout under in-plane shear load. A detailed investigation is made to show the effects of cutout size and cutout aspect ratio on the buckling and postbuckling responses, failure loads and failure characteristics of $(+45/-45/0/90)_{2s}$, $(+45/-45)_{4s}$ and $(0/90)_{4s}$ laminates. The 3-D Tsai-Hill criterion is used to predict the failure of a lamina while the onset of delamination is predicted by the interlaminar failure criterion. In addition, the effects of boundary conditions on buckling loads, failure loads, failure modes, and maximum transverse deflection for a $(+45/-45/0/90)_{2s}$ laminate with and without a square cutout have been presented. It is concluded that because of early onset of delamination at the net section of cutouts before first-ply failure, total strength of the laminate with very small cutouts can not be utilized.

• 콘크리트학회논문집
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• 제15권1호
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• pp.134-142
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• 2003

고강도 콘크리트의 초기 균열 제어를 위해서는 균열 발생의 주요 원인인 자기수축에 대한 실험과 예측, 그리고 감소 방안에 대한 연구가 요구된다. 본 연구에서는 물-결합재비가 0.50~0.27이고 플라이 애쉬 대체율이 0, 10, 20, 30%인 콘크리트의 자기수축을 측정하였으며, 실험결과를 토대로 예측 모델을 제안하였다. 실험 결과, 물-결합재비가 낮아짐에 따라 자기수축이 증가하였으며, 재령 초기에서 자기수축 발현률이 크게 증가하였다. 또한, 플라이 애쉬 대체율이 증가할수록 자기수축이 감소하는 결과를 얻었다. 비록 재령 초기에 큰 자기수축이 발생했다 하더라도 콘크리트의 강성(탄성계수)이 낮은 동안에는 응력은 발생하지 않게 된다. 따라서, 본 연구에서는 콘크리트 강성의 변화를 고려하기 위해 초음파 속도 발현 특성으로부터 콘크리트 강성의 발현 시점을 간접적으로 조사하여 이를 자기수축 모델링에 사용하였다. 실용적인 측면에서, 본 연구에서 제안된 모델은 자기수축과 이로 인해 발생한 응력을 예측하는 데에 유효하게 적용될 수 있을 것으로 기대된다.

• 한국도로학회논문집
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• 제6권4호
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• pp.75-89
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• 2004

콘크리트 포장의 장기 공용성은 시공조건과 환경조건에 크게 좌우된다. 즉 초기에 무작위 균열이나 균열틈이 많이 벌어진 경우 포장수명을 저감시키는 원인이 된다. 시공당시의 온도와 습도, 시멘트와 골재의 종류, 양생조건들은 콘크리트포장의 품질에 영향을 미치는 중요한 요소이다. 그 중에서도 대기온도와 수화열의 증가에 의한 높은 온도차이는 심각한 초기균열을 발생시키는 원인이 되는 것으로 알려져 있다. 본 연구에서는 차광막을 사용하여 콘크리트 슬래브의 온도를 제어하여 초기균열이 발생할 가능성을 낯추고 슬래브질이의 온도차이에 의해 발생되는 curling stress를 줄일 수 있었고, 강도에 있어서는 차광막 설치 구간이 일반시공구간보다 장기강도를 크게 할 수 있음을 확인하였다. 또한 콘크리트포장의 포설 후 72시간의 강도 및 응력을 예측하는 프로그램인 HIPERPAV를 사용하여 초기에 균열이 발생할 가능성을 비교해본 결과 차광막을 설치한 구간이 본 시험시공의 예에서 균열이 발생하지 않을 가능성(reliability)이 차광막을 설치하지 않은 구간(일반시공구간) 72.5%. 차광막설치 구간 95%로 나타나 차광막설치 구간이 차광막을 설치하지 않은 구간보다 균열이 발생하지 않을 가능성을 크게 증가시킬 수 있을 것으로 분석되었다.

• 한국건축시공학회지
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• 제14권2호
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• pp.156-162
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• 2014

본 연구는 PC(Precast Concrete)부재 생산 시 스팀양생 공정을 생략하여 경제적 및 환경적 문제를 해결하고자 상온양생으로 탈형강도(10MPa이상)를 만족시킬 수 있는 조강형 콘크리트를 개발하는데 목적이 있다. 따라서, 조기강도 발현에 반응성이 높은 $C_3S$를 많이 함유하고 있는 조강 시멘트와 $C_3S$의 수화반응을 높이는 경화촉진제를 사용한 조강콘크리트를 평가하였으며, 경화촉진제를 사용한 콘크리트 실험결과는 다음과 같다. 유동성 확인을 위한 슬럼프 플로 시험과 공기량은 목표값을 만족하였다. 경화촉진제를 혼입함에 있어 압축강도는 12시간까지 급격한 발현성상을 나타내었으며, 6~9시간 만에 목표를 만족하였다. 건조수축 및 자기수축의 최대 수축량은 ($-800{\times}10^{-6}$)이하의 값을 나타내어 양호한 것으로 나타났다. 또한, 간이단열온도상승 시험으로 24시간 이내에 Peak 온도를 나타내고 감소하는 것을 확인하였다.

• 한국농공학회지
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• 제17권4호
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• pp.3931-3942
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• 1975

This study was conducted to investigate the strength of soil cement for varied curing temperatures (0,10,20,30,40,50,60$^{\circ}C$) and cement content (3,6,9,12%) in four cement-stabilized soils (KY: sand, MH: sand, SS: sandy loam, JJ:loam). The experimental results obtained from unconfined compressive strength tests were as follows: 1. According to increase of curing temperature as 30,40,50, and 60$^{\circ}C$, the unconfiened compressive strength of soil cement increased, the rate of increase in the early curing period was large, and around 120 hours was suifficient curing time to complete hardening. 2. The strength at 10$^{\circ}C$ decreased to the rate of 30 to 40 percent than that of 20$^{\circ}C$ while the strength at 0$^{\circ}C$ was very small, strength of soil cement increased in cold weather unless that the temperature was below 0$^{\circ}C$ 3. The average maximum temperature, about 30$^{\circ}C$ during July and August in Korea may be recommended for a optimum construction period to increase the strength of soil cement. 4. Accelerated curing time that strength was equivalent to 28-Day norma1 curing decreased in accordance with the increase of curing temperature, and also accelerated curing decreased the effect of cement content. Accelerated curing that strength was equivalent to 28-day normal curing for soil cement of cement content 9% and temperature 60$^{\circ}C$ was 45 hours; KY, 50 hours: MH, 40 hours; SS, 34 hours; JJ. 5. According to the increase of the percent passing of No. 200 sieve, accelerated curing times became shorter to become the required stength. 6. Relation between accelerated curing times and normal curing days was showeda linear of which slope decreased in accordance with the increase of curing temperature, it may be expressed as follows: (1). 30$^{\circ}C$ t=3.6d+6(r=0.97) (2). 40$^{\circ}C$ t=3.2d-5.1(r=0.95) (3). 50$^{\circ}C$ t=2.1d-4.0(r=0.93) (4). 60$^{\circ}C$ t=1.4d+4.0(r=0.90) in which t=accelerate curing time. d=normal curing day. 7. Accelerated curing time that the strength was equivalent to 35kg/$\textrm{cm}^2$ which was the strength of cement brick was 96 hours at temperature 30$^{\circ}C$ to SS 9%, and 120 hours at temperature 50$^{\circ}C$ to JJ 9%, Consequently, a economic soil cement brick may be made in future.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.365-368
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• 2008

본 연구에서는 극히 낮은 물-결합재비를 갖는 240MPa 초고강도 콘크리트를 개발하고자 분말도가 높아 반응속도가 빠르며, 조기강도가 우수하나 극히 낮은 물-시멘트비에서 더욱 우수한 유동성을 확보할 수 있는 고강도용 '하이플로 시멘트'를 주원료로 하고, 기타 초고강도용 혼합재로 실리카흄, 슬래그 미분말 및 특수 혼합재 등을 사용한 다성분계 시멘트 결합재의 최적조합을 도출하였으며, 시멘트 결합재의 분산성과 균질성을 확보하기 위하여 고효율 초고속전단 옴니믹서를 사용하여 프리믹스 타입의 시멘트를 제조하였다. 또한 고속믹싱방법을 통해 초고강도 콘크리트의 유동성을 확보하였으며, 초고강도용 특수골재를 선정하여 실험을 실시한 결과, 수중양생을 실시한 경우 180MPa이상의 강도를 확보하였으며, 증기양생을 실시한 경우 200MPa이상의 강도를 얻을 수 있었고, 최종적으로 특화된 양생방법을 통해 240MPa이상의 안정된 초고강도 콘크리트 품질을 확보하였다.

• International Journal of Advanced Culture Technology
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• 제6권4호
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• pp.152-157
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• 2018

In the late 19th century and early 20th century, Among those of the Northeast Asia three countries, school physical education and military-style gymnastics of Chosun can be regarded as having been the most nationalistic. The adoption of modern physical education in public schools was from the proclamation of 'the Order on Building the Country through Education by King Gojong in February 1895. This paper intends to examine the process of adopting military-style gymnastics education which played the central role in school physical education in the late Chosun period. But, unlike the common guess that military-style gymnastics in public schools in late Chosun would have been full of patriotism and nationalism, the textbooks and teaching contents of Chosun Military Officers' School were very similar to those of Japan, which is an unexpected fact. Therefore, Chosun decided to accept the Japanese-type military-style gymnastics and military training to improve physical strength of youngsters and military power. The fact that, with the advent of modern education, physical education was emphasized above all else has a very important meaning to the history of Korean physical education. Physical activity education emerged as a major education course which had been unthinkable in previous ages. The second characteristics is that the process of adopting military-style gymnastics and its contents were influenced by Japan Third, even if military-style gymnastics was imported from Japan as part of school physical education course in late Chosun period, its aim was to train military man powers for the independence movement against Japan, rather than to develop harmonious body.

• Advances in materials Research
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• 제1권3호
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• pp.205-219
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• 2012

Co-Re alloy development is prompted by the search for new materials for future gas turbines which can be used at temperatures considerably higher than the present day single crystal Ni-based superalloys. The Co-Re based alloys are designed to have very high melting range. Although Co-alloys are used in gas turbine applications today, the Co-Re system was never exploited for structural applications and basic knowledge on the system is lacking. The alloy development strategy therefore is based on studying alloying additions on simple model alloy compositions of ternary and quaternary base. Various strengthening possibilities have been explored and precipitation hardening through fine dispersion of MC type carbides was found to be a promising route. In the early stages of the development we are mainly dealing with polycrystalline alloys and therefore the grain boundary embrittlement needed to be addressed and boron addition was considered for improving the ductility. In this paper recent results on the effect of boron on the strength and ductility and the stability of the fine structure of the strengthening TaC precipitates are presented. In the beginning the alloy development strategy is briefly discussed.

• 한국기계가공학회지
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• 제9권6호
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• pp.59-65
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• 2010

This study deals with the characteristic of refrigerant for heat-treatment deformation control of SCM415 steel. The control of heat-treatment deformation must need the progress of production parts for an industry machine. Most of the deformation is occurred on unequal cooling. The unequal cooling is occurred by a property of quenching refrigeration. When a heated metal is deposited in the refrigeration, the cooling speed is so slow in early period of cooling because of occurring a steam-curtain. After more cooling, the steam-curtain is destroyed. In this progress, the cooling speed is very fast. The object of this study is to control the deformation of heat-treatment for the part of the industry machine by improving the conditions of quenching. The cooling curves and cooling rates of water, oil and polymer solution are obtained and illustrated. From the characteristics of the quenching refrigerant, the effects of heat-treatments on the thermal deformation and fatigue strength are also investigated.

• Journal of Korean Neurosurgical Society
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• 제49권2호
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• pp.139-141
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• 2011

Compression of the ulnar nerve in Guyon's canal can result from repeated blunt trauma, fracture of the hamate's hook, and arterial thrombosis or aneurysm. In addition, conditions such as ganglia, rheumatoid arthritis and ulnar artery disease can rapidly compress the ulnar nerve in Guyon's canal. A ganglion cyst can acutely protrude or grow, which also might compress the ulnar nerve. So, clinicians should consider a ganglion cyst in Guyon's canal as a possible underlying cause of ulnar nerve compression in patients with a sudden decrease in hand strength. We believe that early decompression with removal of the ganglion is very important to promote complete recovery.