• 펄프종이기술
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• 제38권5호
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• pp.54-59
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• 2006

Paperboards used for linerboard of corrugated fiberboard box were coated with different concentrations of polylactic acid (PLA) solution and the effects of harsh environmental conditions such as high humidity and temperature (96% RH at $30^{\circ}C$ for up to 5 days), and freeze-thaw ($-20^{\circ}C$ for a day and then thaw at room temperature for 30 min) conditions on the ring crush (RC) strength of the boards were investigated. One to five percent PLA solutions were coated onto SC manila linerboard ($20{\times}27cm$) using a No. 20 wire bar coater and the ring crush strength was measured using a computer-controlled Advanced Universal Testing System in accordance with TAPPI Test Method T 822 om-93. The RC strength increased significantly when the concentration of coating solution increased and appreciable changes were found when the concentration increased from 0 to 2% (P<0.05). Similar pattern of results was found after 5-day storage at $30^{\circ}C$ and 96% RH. Although such highly humid condition increased moisture content in the samples up to 3.95 from 0.97 times, the RC strength decreased in the range from 29.9 to 48.5%. The freeze-thaw treatment increased the moisture content only up to 1.27% and the reduction in the RC strength ranged from 21.1 to 28.1 %. The results were promising: the samples coated with 5% PLA solution showed 29.9% reduction in the RC strength while that of control was 48.5% during highly humid condition stated above.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.592-600
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• 2005

Ship have cutout inner bottom and girder and floor etc. Ship's structure is used much, and structure strength must be situated, but establish new concept when high stress interacts sometimes fatally the area. There is no big problem usually by aim of weight reduction, a person and change of freight, piping etc.. Because cutout's existence grow up in this place, and elastic buckling strength by load causes large effect in ultimate strength. Therefore, stiffened perforated plate considering buckling strength and ultimate strength is one of important design criteria which must examine when decide structural concept at initial design. Therefore, md, reasonable buckling strength about stiffened perforated plate need to ultimate strength limited design . Calculated ultimate strength varied several web height and cutout's dimension, and thickness in this investigated data. Used program(ANSYS) applied F.E.A code based on finite element method

• 한국생산제조학회지
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• 제7권2호
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• pp.15-22
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• 1998

The effects of shot peening an the fatigue strength are studied in this paper. Applying the multistage shot peening on the material. the relation between the residual stress and fatigue strength compressive is investigated. Observing tensile strength elongation. reduction of area. hardness. and roughness. the results can be summarized as follows ; 1.The change of mechanical properties is small before and after the shot peening is carried out. The change of hardness is also small in high hardness material. 2.The surface roughness does not affect the fatigue strength. but the surface roughness is improved by multi-stage shot peening. 3.The fatigue strength of multi-stage shot peening material is 756MPa and is 1.78 times higher than that of un-peened material. 4.The maximum compressive residual strength of multi-stage shot peening material is -792MPa the fatigue strength seems to be improved by residual stress.

• 대한안전경영과학회지
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• 제12권2호
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• pp.83-87
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• 2010

Functional Concrete Added Titanium Dioxide(TIO2) for photocatalysis was about a result strength Reduction by recent studies. Therefore, The purpose of the study is to review the possibility of TIO2 for using concrete admixture. As a result, Nano TIO2 for concrete admixture helps increased strength of concrete and here are some of the details. The compressive strength and flexural strength of cement mortar added same amount of Nano SF and TIO2 for admixture were development of strength a certain level each other. when Nano admixture use 10%, SF and TIO2 showed development of strength 60% and 40% each other gradually. If I use over 10% Both SF and TIO2, they showed irregular strength variations.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1990년도 가을 학술발표회 논문집
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• pp.125-130
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• 1990

Fly Ash in concrete is known to be effective in improving workability, the reduction of heat of hydration, increasing the long-term compressive strength, and improving durability. Recently, fly ash is consedered an essential material for the high-strength concrete. In this paper, investigations for the strength and workability characteristics was carried out when fly ash was used in the high-strength concrete. As the result, fly ash was effective in increasing the long-term compressive strength, but the short-term compressive strength was gradually decreased with increating fly ash contents. And also the use of superplasticzers was required for providing the proper workability when fly ash contents were increased. The optimum content of fly ash was about 10%.

• Earthquakes and Structures
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• 제9권6호
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• pp.1233-1250
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• 2015

The behavior of reinforced concrete (RC) columns made from high strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength transverse reinforcing bars and three with normal-strength transverse reinforcement, were tested under double curvature bending load. The effects of yielding strength and ratio of transverse reinforcement on the cracking patterns, hysteretic response, shear strength, ductility, strength reduction, energy dissipation and strain of reinforcement were studied. The test results indicated that all specimens failed in splitting failure, and specimens with high-strength transverse reinforcement exhibited better seismic performance than those with normal-strength transverse reinforcement. It also demonstrated that the strength of high-strength lateral reinforcing bars was fully utilized at the ultimate displacements. Shear strength formula of short concrete columns, which experienced a splitting failure, was proposed based on the Chinese concrete code. To enhance the applicability of the model, it was corroborated with 47 short concrete columns selected from the literature available. The results indicated that, the proposed method can give better predictions of shear strength for short columns that experienced a splitting failure than other shear strength models of ACI 318 and Chinese concrete codes.

• 자원리싸이클링
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• 제19권6호
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• pp.93-101
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• 2010

본 연구에서는 전기로 환원슬래그를 시멘트 혼화재로 이용하였을 때의 전기로 환원슬래그의 수화반응 특성과 압축강도 특성을 연구하였다. 전기로 환원슬래그에는 17.1%의 f-CaO 및 속경성 클링커 광물인 37.1%의 $C_{11}A_7CaF_2$와 21.0%의 $Ca_3A$가 함유되어 있었다. 보통 포틀랜드시멘트(OPC, Ordinary Portland Cement)에 전기로 환원슬래그를 30%까지 치환할 경우, 초결 및 종결시간이 각각 305분과 425분에서 10분과 30분으로 단축되는 급결성을 보였다. OPC에 전기로 환원슬래그의 치환량이 7%까지 증가됨에 따라 혼합시멘트의 압축강도는 OPC보다 높아졌으나, 7%이상에서는 점차 압축강도가 낮아져 20%이상 치환하였을 때에는 OPC보다 초기강도 및 장기강도가 모두 낮았다. 전기로 환원슬래그 자체의 수화반응 생성물을 조사한 결과, $C _{11}A_7CaF_2$는 물과 반응하여 $C_3AH_6$로 변화되었다. 그러나 OPC에 환원슬래그를 치환하여 사용할 경우, 환원슬래그의 치환율이 높아짐에 따라 f-CaO가 많아지고 준안정성의 수화물인 $C_4AH_{13}$의 생성량이 증가되기 때문에 OPC에 환원슬래그를 7%미만으로 치환하여 사용해야만 안정된 경화체를 형성하여 압축강도가 OPC보다 높아졌다.

• 한국건설순환자원학회논문집
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• 제7권3호
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• pp.62-69
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• 2012

본 연구에서는 유화처리 폐식용유(이하 EWCO)의 현장 및 실무에 적용하기 위해 적절한 혼입률을 도출하고자 유화처리 폐식용유 사용이 고강도 콘크리트의 공학적 특성 및 자기수축에 미치는 영향 등을 기존의 수축저감제와 비교 분석하였다. 실험결과, 굳지 않은 콘크리트의 특성으로 먼저 유동성은 SR의 경우 치환율 0.25%에서 Plain에 비해 약 5% 저하하는 것으로 나타났고, 치환율에 따라 약 30~40% 급격히 저하하는 것으로 나타났다. 반면 EWCO의 경우는 치환율에 따라 Plain 대비 약 5~10% 정도의 다소 미미한 차이로 유동성이 저하하였다. 공기량, 단위용적질량 및 응결시간은 Plain과 거의 유사한 경향을 나타내 수축저감용 혼화제 사용에 있어 이와 같은 물성에 큰 영향이 없는 것으로 나타났다. 압축강도는 EWCO의 경우 초기재령에서는 Plain과 거의 유사한 강도값을 나타냈고, 재령이 경과할수록 다소 저하하는 것으로 나타났다. 재령 28일에서는 치환율에 따라 약 5~10% 정도 저하하는 것으로 나타났다. 반면 SR의 경우는 초기재령에서 Plain에 비해 저하되는 것으로 나타났고, 재령 28일에서는 치환율 0.75% 이상에서 Plain과 약 11~12% 정도 강도가 저감되는 것으로 나타났다. 자기수축은 EWCO의 경우 치환율에 따라 Plain 대비 약 14~33% 저감되는 것으로 나타났고, SR의 경우는 약 16~29% 저감되는 것으로 나타났다. 이상을 종합해보면 EWCO를 자기수축저감제로 사용할 경우 유동성 및 공기량에 큰 영향이 없으며, 기존의 SR에 비교하여도 자기수축 저감성능이 우수한 것으로 판단되는바 강도저하 측면을 고려하고 실무의 경제성을 고려시 EWCO 0.5~0.75% 전후가 효과적인 것으로 판단된다.

• 한국자동차공학회논문집
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• 제17권2호
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• pp.104-111
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• 2009

In this paper, optimization for frontal crashworthiness is carried out for the weight reduction design of an auto-body member with the advanced high strength steels(AHSS) such as 780TRIP and 780DP. The frontal crashworthiness is evaluated in order to optimize thicknesses for the front rail member of the ULSAB-AVC, Thicknesses of the front rail member with AHSS are optimized by comparison of crushing distance, absorbed energy and the deceleration for the auto-body with the response surface methodology. The results demonstrate that the crashworhiness of the front rail member with the optimum thicknesses of the AHSS is similar to analysis results obtained from the ULSAB-AVC project. The results also show that the weight reduction design is performed by substituting the AHSS for conventional structural steels such as 440E in the auto-body members.

• 소성∙가공
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• 제18권6호
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• pp.488-493
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• 2009

The very big springback of advanced high strength steel(AHSS) sheets invokes undesired shape defects, which can be generally eliminated by die correction or process parameter control. The springback reduction by controlling the forming process parameters is easy for the application, but limited for the bulky achievement. In this study, the effective die correction method, which obtains the modification of tool shape from the relationship between die design variable and springback, is introduced and is applied to the TWB tool of automotive side rail to show the validity and usefulness. Among the die correction trials repeatedly performed, the first trial is carried out by correcting the tool shape to the opposite direction to the springbacks of several tool sections. Next trials are done by extrapolating the springbacks of among the original tool uncorrected and the tools corrected negative amounts of the springback and by finding tool shapes without springbacks. After the angle of side wall and radius of curvature of horizontal bottom floor are chosen as design variables in the tool design of side rail, the tool shape is corrected 3 times. The accuracy of final shape within the assembly limit of 1mm and the springback reduction of 75.8% compared to the uncorrected tool are achieved.