• Title/Summary/Keyword: 초기경화

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Estimation of Transient Creep C(t)-integrals for SE(B) Specimen Under Elastic-Plastic-Creep Conditions (탄성-소성-크리프 상태에서 SE(B) 시편의 천이크리프 C(t)-적분 평가)

  • Lee, Han-Sang;Je, Jin-Ho;Kim, Dong-Jun;Kim, Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.9
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    • pp.851-857
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    • 2015
  • In this paper, we estimate the time-dependent C(t) integrals under elastic-plastic-creep conditions. Finite-element (FE) transient creep analyses have been performed for single-edge-notched-bend (SEB) specimens. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step load. We consider both the same stress exponent and different stress exponents in the power-law creep and plasticity to elastic-plastic-creep behavior. To estimate the C(t) integrals, we compare the FE analysis results with those obtained using formulas. In this paper, we propose a modified equation to predict the C(t) integrals for the case of creep exponents that are different from the plastic exponent.

Evaluation of Engineering Properties in Early-Age Concrete with TDFA (TDFA를 혼입한 초기재령 콘크리트의 공학적 특성 평가)

  • Park, Jae-Sung;Park, Sang-Min;Kim, Hyeok-Jung;Kwon, Seung-Jun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.20 no.5
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    • pp.1-8
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    • 2016
  • This paper presents an evaluation of engineering properties in TDFA(Tire Derived Fuel Ash)- based concrete in early age. Concrete containing 0.5 of w/b(water to binder) ratio and 20% of FA(Fly Ash) replacement ratio are prepared, and FA content are replaced with TDFA from 3% to 12% for evaluating the effect of TDFA on fresh and hardened concrete properties. With higher than 6% of TDFA replacement ratio, workability is significantly worsened but it is improved with more SP(Super plasticizer) and AE(Air Entrainer) agent. Concrete with 6~12% of TDFA shows reasonable strength development and better resistance to carbonation and chloride attack in spite of early-aged condition. However concrete with 6% TDFA shows poor resistance to freezing and thawing action due to insufficient air content. If air content and workability are obtained, replacement of TDFA to 12% can be used for concrete with FA.

Three-Point Bending Fatigue Properties of Austenitic 304 Stainless Steel Sheets for Membrane (Membrane용 오스테나이트계 304 스테인리스강 판재의 3점 굽힘피로 특성)

  • Lee Tae-Ho;Kim Sung-Joon;Kim Hyoung-Sik;Kim Cheol-Man;Hong Seong-Ho
    • Journal of the Korean Institute of Gas
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    • v.3 no.3 s.8
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    • pp.1-8
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    • 1999
  • Three-point bending fatigue properties of austenitic 304 stainless steel sheets were investigated at room temperature and LNG temperature($-162^{\circ}C$) in the strain range from 0.43 to $1.7\%$. The fatigue properties at $-162^{\circ}C$ were superior to those at room temperature due to the higher volume fractions of deformation-induced martensite. The cyclic hardening behavior owing to the deformation- induced martensite transformation was detected in both specimens. In room temperature testing, the mean load amplitude increased steadily with cycles, meaning that cumulative plastic incubation strain was required for martensite transformation. On the contrary, in $-162^{\circ}C$ tested specimen, the mean load amplitude increased rapidly within a few cycles due to the rapid transformation of martensite, and slightly decreased after the maximum is reached probably due to dynamic recovery.

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Strength Development Properties of Alkali-Activated Slag Mortar by Curing Conditions (양생조건에 따른 알칼리활성슬래그 모르타르의 강도발현 특성)

  • Song, Jin-Gyu;Kim, Byeong-Jo;Oh, Myeong-hyeon
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2015.07a
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    • pp.216-217
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    • 2015
  • This study consist of research on the strength development properties of alkali activated slag(AAS) by differential combination of activators, initial protecting and curing conditions. 3 type of binders cured in the atmosphere, underwater and sealed were estimated compressive strength of 3, 7 and 28 days. Test results showed that strength development properties of binders varied with initial protecting and curing conditions because of ionized anions in pore water.

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생쥐 초기 배아에서 Aquaporin 8과 9의 발현에 관한 연구

  • 신현상;계명찬;강수만;이성은;이지원;강한승;김문규
    • Proceedings of the Korean Society of Developmental Biology Conference
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    • 2003.10a
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    • pp.68-68
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    • 2003
  • Aquaporin은 막관통 통로 단백질(transmembrane channel protein)로서, 삼투압의 농도구배에 따라 세포막을 가로질러 물분자를 이동시키는 기능을 하고 있다. 포유류 초기배아에서 포배강 형성은 영양외배엽세포에서 $Na^+ / K^+$ATPase에 의한 이온 농도 구배가 형성되면 auqaporin에 의해 물이 포배강으로 유입되면서 이루어진다. 본 연구에서는 생쥐 초기배아에서 반정량적인 역전사 중합효소 연쇄반응 방법(semi-quantitative RT-PCR)과 실시간 역전사 중합효소 연쇄반응 방법(real-time RT-PCR)을 통하여 AQP8과 9의 mRNA발현을 조사하고 다중 면역형광현미경 방법(confocal immunofluorescence microscopy)을 통해 단백질 발현양상을 분석하였다. AQP8 mRNA는 상실기까지 발현되지 않다가 포배기에 이르러 발현되었고 AQP9 mRNA는 수정란에서부터 발현되어 포배기에는 유의할 정도로 증가하였다. 따라서 AQP8 mRNA는 배아유전자가 활성화되어 나타나는 것이고 AQP9 mRNA는 모계유전자 기원임을 알 수 있었다. AQP8 단백질은 상실배 단계까지 발현되지 않다가 포배시기에 영양외배엽세포사이의 접합면에 발현되었고 AQP9 단백질은 상실배 시기에 할구 사이의 인접 부위에서 강하게 발현되었다가 포배시기에는 세포간의 접합면에 약하게 발현하는 경향을 나타내었다. 실시간 역전사 중합효소 연쇄반응 방법으로 조사한 결과 포배에서 물과 글리세롤을 통과시키는 AQP9는 mRNA의 발현양이 AQP8보다 약 4배 정도 많았다. 또한 포배기에 이르러서야 물만을 통과시키는 AQP8의 발현이 나타나는 것을 보아 포배강 형성시 외부에서 영양외배엽을 통해 포배강으로 유입되는 물의 이동(trans- trophectodermal water movements)에 AQP9보다 AQP8이 더 중요하게 관여할 것으로 사료된다., K, Pb, Cd, Cr, Co, Cu, Ni)을 측정하였다. 실험 조건1의 결과로서 각 국의 유아용 일회용 기저귀의 중금속 함량은 거의 유사한 경향을 나타내었으며 Cr, Zn, Pb, Ni, Mn, Mg, Li, K는 detection limit(2 ppm) 이하였고, Cd, Fe, Co, Cu, Ca, Al, Sr는 검출되었지만 기준치 이하였다. 실험 조건2의 결과로서 측정 항목(Cr, Sb, Cd, Pb, Ni, Co, Cu)중 Cr, Cd, Ni, Cu는 detection limit(0.1 ppm) 이하였고, Sb, Pb, Co는 검출되었지만 기준치 이하였다.았다. 4%의 경우에는 8$0^{\circ}C$이하로 온도를 낮추는 것이 좋은 상태를 나타내었다. 이와 같은 결과는 일반적으로 화학적 레팅을 4%, 7%에서한 선행결과와 상당히 다른 결과이다.염 농도가 증가할수록 감소 현상을 보였다.X>, 75BG30은 8.6$\mu\textrm{m}$, 75BG40은 7.02$\mu\textrm{m}$로 나타났다. 따라서 경화제 양에 관계없이 10$\mu\textrm{m}$ 이하로 나타나, 경화제 10$m\ell$만으로 미세한 크기를 얻을 수 있음을 알 수 있다. 젤리 강도 변화에 따른 차이는 300BF는 78.09$\mu\textrm{m}$ 300BG는 56.32$\mu\textrm{m}$로, 75BF나 75BG에 비하여 현저히 증가하여, 젤라틴의 젤리 강도는 캡슐 제조 조건의 주요한 변수임을 알 수 있다.추출물 투여시 혈당강하 및 혈중콜레스테롤 강하가 나타났으며, 상엽복합추출물 투여와 운동을 병행시 이러한 감소 효과가 더 뚜렷하게 나타났다.교육의 적임자로 보는 시각이 비교적 높았고 약 1/2정도는 영양교육에 참여하겠다는 의지를 가지고 있을 뿐만 아니라 실제로 영양지도를

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A Study on the Hydration Reaction Model of Expansive Additive of Ettringite-Gypsum Type (에트링가이트-석탄 복합계 팽장재의 수화반응 모델에 관한 연구)

  • Park Sun Gyu;Takahumi Noguchi;Kim Moo-Han
    • Journal of the Korea Concrete Institute
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    • v.17 no.4 s.88
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    • pp.581-586
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    • 2005
  • High-performance concrete (HPC), which is particularly sensitive to self-desiccation, is required to be durable even in severe environmental conditions, i.e. costal area, cold district, etc. However, in recent years, some attention was particularly given to cracking sensitivity of high performance concrete at early age. It has been argued and demonstrated experimentally that such concrete undergoes autogenous shrinkage due to self-desiccation at early age under restrained condition, nd, as a result, internal tensile stress may develop, leading to micro cracking and macro cracking. This shrinkage-introduced crack produces a major serviceability problem for concrete structures. One possible method to reduce cracking due to autogenous shrinkage is the addition of expansive additive. Tests conducted by many researches have shown the beneficial effects of addition of expansive additive for reducing the risk of autogenous shrinkage-introduced cracking. However, the research on hydration model of expansion additive has been hardly researched up to now. This paper presents a study of the hydration model of Ettringite-Gypsum type expansive additive. As a result of comparing forecast values with experiment value, proposed model is shown to expressible of hydration of expansive additive.

Synthesis and PSA Properties of Acryl Modified Resin for Semiconductor Wafer (반도체 웨이퍼용 아크릴 변성 수지의 합성 및 점착 특성)

  • Sim, Jong Bae;Shin, Kyoung Sub;Hwang, Taek Sung
    • Journal of Adhesion and Interface
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    • v.11 no.2
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    • pp.63-69
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    • 2010
  • In this study, acryl resin PSA containing hydroxyl group based on 2-EHA (2-ethyl hexyl acrylate), 2-EHMA (2-ethyl hexyl methacrylate), 2-HEA (2-Hydroxy ethyl acrylate), acrylic acid was synthesized and then, isocyanate modified acryl resin PSA prepared with adduct reaction according to the amount of MOI (Methacryloyloxyethyl isocyanate) or 2-isocyanatoethyl methacrylate that can improve the curing property. This research shows that the initial PSA and peel adhesion are decreased according to the increase of the amount of the MOI and isocyanate curing agent. After UV irradiating, the peel adhesion is decreased with increasing the amount of the MOI (Methacryloyloxyethyl isocyanate) and isocyanate curing agent, because of the high curing property.

A Prediction Model on Porosity of Hardened Cement Paste under High Temperatures (고온시의 경화된 시멘트 페이스트의 공극률 예측모델)

  • Lee, Jae-Sung;Jung, Sung-Jin;Jung, Young-Han;Kim, Heung-Youl;Kim, Hyung-Jun
    • Fire Science and Engineering
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    • v.23 no.3
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    • pp.103-109
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    • 2009
  • The thermal degradation of concrete results mainly from two mechanisms. The first one is related to phase transformations of constituents at different temperatures. The initial constituents transform to other phases due to elevated temperature. The second mechanism is related to the temperature sensitivity of the mechanical properties of the constituents in concrete. Therefore, the degradation of concrete under high temperatures must be studied from both mechanical and chemical points of view. This study was performed as a basic study to propose the material models of concrete exposed to high temperatures considering above two mechanisms. This study presents a prediction model on the porosity of hardened cement paste considering phase changes according to temperature increase.

Material model optimization for dynamic recrystallization of Mg alloy under elevated forming temperature (마그네슘 합금의 온간 동적재결정 구성방정식 최적화)

  • Cho, Yooney;Yoon, Jonghun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.6
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    • pp.263-268
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    • 2017
  • A hot forming process is required for Mg alloys to enhance the formability and plastic workability due to the insufficient formability at room temperature. Mg alloy undergoes dynamic recrystallization (DRX) during the hot working process, which is a restoration or softening mechanism that reduces the dislocation density and releases the accumulated energy to facilitate plastic deformation. The flow stress curve shows three stages of complicated strain hardening and softening phenomena. As the strain increases, the stress also increases due to work hardening, and it abruptly decreases work softening by dynamic recrystallization. It then maintains a steady-state region due to the equilibrium between the work hardening and softening. In this paper, an efficient optimization process is proposed for the material model of the dynamic recrystallization to improve the accuracy of the flow curve. A total of 18 variables of the constitutive equation of AZ80 alloy were systematically optimized at an elevated forming temperature($300^{\circ}C$) with various strain rates(0.001, 0.1, 1, 10/sec). The proposed method was validated by applying it to the constitutive equation of AZ61 alloy.

Effects of Shrinkage Reducing Agent (SRA) Type and Content on Mechanical Properties of Strain Hardening Cement Composite (SHCC) (수축저감제의 종류 및 혼입률에 따른 변형경화형 시멘트복합체의 역학적 특성)

  • Han, Seung-Ju;Jang, Seok-Joon;Khil, Bae-Su;Choi, Mu-Jin;Yun, Hyun-Do
    • Journal of the Korea Concrete Institute
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    • v.28 no.1
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    • pp.41-48
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    • 2016
  • This research investigates the effects of shrinkage reducing agent (SRA) on the mechanical behavior of strain-hardening cement composite (SHCC). SHCC material with specified compressive strength of 50 MPa was mixed and tested in this study. All SHCC mixes reinforced with volume fraction of 2.2% polyvinyl alcohol (PVA) fiber and test variables are type and dosage of shrinkage reducing agents. The shrinkage reducing materials used in this study are phase change material as the thermal stress reducing materials that have the ability to absorb or release the heat. The effect of SRA was examined based on the change in length caused by shrinkage and hardened mechanical properties, specially compressive, tensile and flexural behaviors, of SHCC material. It was noted that SRA reduces change in length caused by shrinkage at early age. SRA can also improve the tensile and flexural strengths and toughness of SHCC material used in this study.