• 콘크리트학회논문집
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• 제24권4호
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• pp.491-498
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• 2012

이 연구는 시멘트 콘크리트 포장의 보수나 프리캐스트 제품용으로 사용되는 UP-MMA 폴리머 콘크리트의 경화수축, 열팽창계수 및 탄성계수에 대한 연구이다. 이를 위해 UP-MMA비, SRA 첨가량, 시험온도 등을 변수로 하여 경화수축 시험과 UP-MMA비에 따른 열팽창과 압축응력-변형률에 대하여 시험을 실시하였다. 그 결과 경화수축은 29.2~$82.6{\times}10^{-4}$으로 UP 비율과 시험온도에 큰 영향을 받는 것으로 나타났다. 그리고 열팽창계수는 21.6~$31.2{\times}10^{-6}/^{\circ}C$, 탄성계수는 2.8~$3.3{\times}10^4MPa$, 극한변형률은 0.00381~0.00418이었으며, 이는 UP-MMA비에 크게 영향을 받는 것으로 나타났다. 이러한 결과들은 UP-MMA 폴리머 콘크리트의 적용을 위한 설계에 중요한 기초자료로 이용될 수 있을 것이다.

• Elastomers and Composites
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• 제42권4호
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• pp.201-208
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• 2007

본 연구에서는 충전된 고무재료의 온도 변화에 대한 치수 안정성을 고찰하기 위해 카본블랙 또는 실리카가 충전된 NR과 SBR의 열변화시 발생하는 수축력과 팽창력을 측정하였다. 일정 길이로 인장된 시편의 온도를 올렸을 때 고무사슬의 엔트로피적 변화에 의해 수축력이 발생하였다. 카본블랙이나 실리카가 첨가된 NR의 경우 충전제 함량이 증가함에 따라 최대 열수축력 값이 감소하였으나, SBR의 경우는 30 phr 함량에서 미충전 고무보다 높은 열수축력 값을 보였다. 압축된 시편의 열팽창력 측정의 경우, 카본블랙을 첨가한 NR의 열팽창력은 거의 변화가 없었으나, SBR은 카본블랙 양의 증가와 함께 최대 팽창력 값이 증가하였다. 실리카를 첨가했을 경우 NR, SBR시편 모두 첨가량이 증가할수록 최대 열팽창력 값이 증가하였다.

• 대한정형외과스포츠의학회지
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• 제1권1호
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• pp.37-42
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• 2002

목적: 재건술의적응이되지않는전,후방십자인대손상환자에서radiofrequency 방식을이용한열위축술을시행하여술기및단기추시결과를보고하고자한다. 대상및방법 : 재건술의적응이되지않는전방십자인대9예, 후방십자인대5예를대상으로하였으며평균추시기간은6개월이었다. 결과 : 일상생활에서느꼈던불안정성은감소됐으며파행이나통증등이현저하게호전되었다. 다만후방십자인대에서시행한경우시간이지남에따라다시슬관절이완이증가하는소견을관찰할수있었다. 결론 : Radiofrequency를이용한열위축술은많은활동을요하는젊은사람의슬관절십자인대손상에서, 특히경도의부분파열및수술의적응이되지않는이완환자에서증상을보일경우시도해볼수있는술식중의하나로추천할만하다. 그러나본결과는단기추시이므로장기추시와대조군연구가요할것으로사료된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.95-100
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• 2003

The shrinkage of high strength/high performance concrete is very important property for the good working of a structure since it very often generates early age cracking due to thermal and autogenous shrinkage. Autogenous shrinkage occurs as a result of internal moisture depletion due to hydration and temperature-induced effects. The level of autogenous shrinkage occurring due to hydration also depends on temperature history at very early age. It is necessary that effect of temperature on autogenous shrinkage is investigated since the stress generated due to autogenous shrinkage is quantified. In this study, Effect of hydration heat evolution on autogenous shrinkage of high strength concretes with W/C=25-40% was investigated.

• 콘크리트학회논문집
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• 제14권3호
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• pp.382-391
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• 2002

본 연구에서 초기재령 콘크리트의 크리프 특성을 고려한 단면 내 온도 및 수축응력을 구하는 3차원 유한요소 해석 프로그램을 개발하기 위한 수치해석 절차에 관하여 정립하였다. 최근 들어 구조물의 노후화에 따른 콘크리트의 내구성에 대한 관심이 고조되고 있고, 초기재령에서 발생하는 균열은 구조물의 내구성 및 사용성과 같은 장기적인 성능에 큰 영향을 미친다. 많은 토목 기술자들이 초기재령 콘크리트의 체적변화에 의한 응력 및 균열 문제를 심도 깊게 다루지 않는 데는 장기적인 내구성과 사용성에 대한 인식이 부족하고, 경화가 진행되는 콘크리트의 체적변화는 매우 복잡한 영향인자를 고려해야 되기 때문이다. 또한 초기재령 콘크리트의 체적변화로 인한 응력을 예측하는 기존 프로그램들은 주로 수화열에 의한 온도 및 열응력 해석에 국한되거나, 수화과정과 연계되지 않은 습도분포에 의한 수축 응력해석을 대상으로 한다. 따라서 본 연구에서는 초기재령 콘크리트의 체적 변화에 의한 모든 응력 요소를 하나의 통합적인 해석 시스템으로 구성하여, 초기재령 콘크리트의 균열 제어 수단으로 활용하고자 한다. 본 연구는 초기재령 콘크리트의 온도 및 수분에 관련된 재료 물성 뿐 만 아니라 역학적 특성 등 모든 재료 물성을 수화도에 기초하여 모델링하였다. 또한 콘크리트가 강성을 가지는 시점부터의 초기재령 크리프 실험을 수행하고, 그 결과로부터 수화도에 따른 크리프 거동을 모델링하여 해석 프로그램에 반영하였다. 개발된 해석프로그램을 이용하여 수치해석 결과와 실험결과를 비교하여 그 타당성을 검증하고, 해석 예제를 통하여 각 변형률 성분에 의한 잔류 응력의 변화 양상을 비교, 분석하였다.

• 한국전기전자재료학회논문지
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• 제36권2호
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• pp.151-157
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• 2023

Integrating dielectric materials into LTCC is a convenient method to increase the integration density in electronic circuits. To enable co-firing of the high-k and low-k dielectric LTCC materials in a multi-material hetero-laminate, the shrinkage characteristics of both materials should be similar. Moreover, thermal expansion mismatch between materials during co-firing should be minimized. The alternating stacking of an LTCC with silica filler and that with calcium-zirconate filler was observed to examine the use of the same glass in different LTCCs to minimize the difference in shrinkage and thermal expansion coefficient. For the LTCC of silica filler with a low dielectric constant and that of calcium zirconate filler with a high dielectric constant, the amount of shrinkage was examined through a thermomechanical analysis, and the predicted appropriate fraction of each filler was applied to green sheets by tape casting. The green sheets of different fillers were alternatingly laminated to the thickness of 500 ㎛. As a result of examining the junction, it was observed through SEM that a complete bonding was achieved by constrained sintering in the structure of 'calcium zirconate 50 vol%-silica 30 vol%-calcium zirconate 50 vol%'.

• Journal of Advanced Marine Engineering and Technology
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• 제33권1호
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• pp.90-96
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• 2009

Injection molding process is one of the most important methods to produce plastic parts with high efficiency and low cost. Today, injection molded parts have been increased dramatically the demand for high strength and quality applications. This report investigates that the optimum injection molding condition for minimum of shrinkage. Molding shrinkage is occurred by several reasons such as thermal shrinkage, a hardening process and compressibility. This report concentrate on shrinkage by a hardening process. As Change a holding pressure and holding time, checked deflections of X, Y, Z directions by shrinkage based on same condition. In conclusion, it was found that holding pressure is stronger and holding time is longer, the deflection by shrinkage is smaller because injection molding needs enough time for cooling and high density. The FEM Simulation CAE tool. Moldflow, is used for the analysis of injection molding process.

• Advances in concrete construction
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• 제10권6호
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• pp.537-546
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• 2020

Exterior walls in buildings are exposed to various forms of thermal loads, which depend on the positions of walls. Therefore, one of the efficient methods for improving the energy competence of buildings is improving the thermal properties of insulation plaster mortar. In this study, lightweight fine aggregate (LWFA) and micro rubber ash (MRA) from recycled tires were used as partial replacements for sand. The flow ability, unit weight, compressive strength, tensile strength, thermal conductivity (K-value), drying shrinkage and microstructure scan of lightweight rubberized mortar (LWRM) were investigated. Ten mixtures of LWRM were prepared as follows: traditional cement mortar (control mixture); three mixes with different percentages of LWFA (25%, 50% and 75%); three mixes with different percentages of MRA (2.5%, 5% and 7.5%); and three mixes consisting both types with determined ratios (25% LWFA+5% MRA, 50% LWFA+5% MRA and 75% LWFA+5% MRA). The flow ability of the mortars was 22±2 cm, and LWRM contained LWFA and MRA. The compressive and tensile strength decreased by approximately 64% and 57%, respectively, when 75% LWFA was used compared with those when the control mix was used. The compressive and tensile strength decreased when 5% MRA was used. By contrast, mixes with determined ratios of LWFA and MRA affected reduced unit weight, K-value and dry shrinkage.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2001년도 학술발표회 발표논문집
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• pp.193-197
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• 2001

The growth in concrete structures repair has prompted major efforts to develop high early strength concrete. The internal or external restraint of thermal shrinkage movements could thus generate tensile stresses in concrete structures if it is used rapid setting repair concrete. Restrained shrinkage and thermal stresses could produce microcracks in concrete which increase its permeability and accelerate its long-term deterioration under weathering and load effects. This study aims at evaluation and increase of the engineering properties of high early strength concrete using regulated set cement.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.589-592
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• 2005

Molding shrinkage s variation is one of the problems to be solved in conventional injection molding. Despite many trying-out has been to solve these, intrinsic causes of shrinkage such as orientation and thermal exchange between melt and mold has yet not solved. For reducing shrinkage and residual stress on molding, injection compression molding process was invented. In this study, experiments about effect of injection compression molding's parameters on shrinkage of molding were conducted with PMMA and compared with conventional injection molding's shrinkage. Before the injection compression molding experiment, molding shrinkage rate was predicted by analyzing pvT graph and was compared with the results of experiment. The shrinkage rate of injection compression molding was lower than convention injection molding' one but was different from the predicted shrinkage. The reason was observed that experiment mold as not positive type, flowing backward of melt into nozzle and unreasonable mechanism of injection molding machine.