• Steel and Composite Structures
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• 제2권2호
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• pp.85-98
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• 2002

The aim of the paper is to present some results about the influence of rheological phenomena on steel-concrete composite beams. Both the cases of slab with normal and high performance concrete for one and two-span beams are analysed. A new finite element model that allows taking into account creep, shrinkage and cracking in tensile zones for concrete, along with non-linear behaviour of connection, steel beam and reinforcement, has been used. The main parameters that affect the response of the composite beam under the service load are highlighted. The influence of shrinkage on the slip over the supports is analysed, together with the cracking along the beam. At last, by performing a collapse analysis after a long-term analysis, the influence of rheological phenomena on the ductility demand of connection and reinforcement is analysed.

• Elastomers and Composites
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• 제44권3호
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• pp.323-328
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• 2009

고분자 용융 같은 물질의 유변학적인 성질은 전단 흐름에서 복잡한 비 뉴톤 유동 현상을 보인다. 이들 유동성질은 유동단위와 유동부분 사이의 상호작용의 특성에 의하여 결정된다. poly(vinyl alcohol) hydrogel의 비 뉴톤유동 곡선을 cone-plate 레오메타로 여러 온도와 여러 농도 조건에서 얻었다. PVA hydrogel의 유동 곡선을 비 뉴톤 유동식에 적용시켜 유동 파라메타를 얻었다. 유동현상은 전단 속도가 증가함에 따라 전단박화의 틱소트로피 현상을 나타내었다.

• 한국응용과학기술학회지
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• 제32권3호
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• pp.386-393
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• 2015

콜로이드 분산계와 같은 복잡한 물질의 유변성질은 전단 흐름이 일어날 때 비뉴톤 유동현상을 나타낸다. 이들 유변성질은 유동단위의 성질과 유동 세그먼트 사이의 상호작용에 의하여 영향을 받는다. 유동곡선을 이론적인 틱소트로피식에 적용하여 여러 틱소트로피 유동 곡선에 대한 유동파라메타, 완화시간, $({\beta}_2)_0$, 구조적인 요인, $C_2$, 전단 모듈러스, $X_2/{\alpha}_2$을 구하였다. 유변 파라메타의 변화는 비뉴톤 유동, 점도, 유동 세그먼트의 유동 활성화 에너지와 직접적인 관계가 있다.

• 대한의용생체공학회:의공학회지
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• 제18권2호
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• pp.187-196
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• 1997

The three-dimensional flow analysis using the finite volume method is presented to compare the steady flow characteristics of blood with those of blood substitutes such as water and aqueous polymer solution in an idealized double branching model. The model is used to simlllate the region of the abdominal aorta near the celiac and superior mesenteric branches. Apparent viscosities of blood and the aqueous Separan solution are represented as a function of shear rate by the Carreau model, Water and aqueoiu Separan AP-273 500wppm solution are frequently used as blood substitutes in vitro experiments. Water is a typical Newtonian fluid and blood and Separan solution are non-Newtonian fluids. Flow phenomena such as velocity distribution, pressure variation and wall shear stress distribution of water, blood and polymer solution are quite different due to differences of the rheological characteristics of fluids. Flow phenomena of polymer solution are qualitatively similar to those of blood but the phenomena of water are quite different from those of blood and polymer solution. It is recommended that a lion-Newtonian fluid which exhibits very similar rheological behavior to blood be used in vitro experiments. A non-Newtonian fluid whose rheological characteristics are very similar to those of blood should be used to obtain the meaninylll hemodynamic data for blood flow in vitro experiment and by numerical analysis

• 한국응용과학기술학회지
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• 제32권4호
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• pp.661-668
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• 2015

The surface rheological properties of polymer monolayer show complicated non-linear viscoelastic flow phenomena when they are subjected to spreading flow. These spreading flow properties are controlled by the characteristics of flow units. The kinetics of the formation of an interfacial film obtained after spreading poly(diisobutylene maleic acid) at air-water interface were studied by measuring of the surface pressure with time. The experimental data were analyzed theoretically according to a nonlinear surface viscoelastic model. The values of dynamic modulus, static modulus, surface viscosities and rheological parameters in various area/ monomer were obtained by appling experimental data to the equation of nonlinear surface viscoelastic model.

• 한국막학회:학술대회논문집
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• 한국막학회 1995년도 추계 총회 및 학술발표회
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• pp.5-9
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• 1995

In the dry-jet-wet-spinning process of a hollow fiber membrane, the polymer solution is pumped into a coaxial tube, jet spinneret. The threadline emerging from the spinneret is stabilized by an internal coagulating medium(liquid or gas) as it emerges from the jet orifice. The nascent hollow thread is further stabilized in a quench bath as shown in Fig. 1. In this scheme, three mechanism of formatiota(temperature gradient, solvent evaporation, and solvent-nonsotvent exchange) can be combined. The changes which promote stabilization often play a dominant role in determining the ultimate fiber wall structure as well. Hence, in pratice, hollow fiber stabilization and development of membrane structure are commonly inseparable. However, fiber dimension(the inside diameter and wall thickness of the hollow fiber) is mainly a rheological problem and is determined by dope pumping rate, spinneret diatance from the coagulation bath, inner coagulant flow rate, and fiber draw-rate. Besides rheological phenomena play a prominent part in the final properties of the hollow fiber.

• Korea-Australia Rheology Journal
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• 제11권4호
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• pp.287-291
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• 1999

The tube model theory of entangled polymer presumes that the polymer chain holds its equilibrium contour length under certain conditions of flow; at times longer than a certain characteristic time, ${\tau}_k$, in the stress relaxation process following any flow history; in steady flow of rates smaller than ${{\tau}_k}^{-1}$; etc. Rheological phenomena associated with this presumption are discussed.

• 소성∙가공
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• 제12권1호
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• pp.3-10
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• 2003

The formation of surface defects associated with Jotting in injection molding is related to the geometries of cavity and fate, operational conditions and the rheological properties of polymer. In this study we have examined jetting phenomena in injection molding process for the throe kinds of PCs which have different molecular weights and structures, PBT and PC/ABS alloy with several injection speeds. We have used various cavity shapes those are tensile, flexural and impact test specimens with various gates and cavity thicknesses. Through this study we have observed that the jetting is related to the dic swell of material. This means that the jotting is strongly affected by the elastic flow property rather than the viscous flow property in viscoelastic characteristics of molten polymer. Different resins have different elastic properties, and elastic flow behavior depends on the shear rate of flow, i.e. injection speed. Large die swell would eliminate jetting however, the retardation of die swell would stimulate jetting. In the point of mole design, reducing the thickness ratio of cavity to gate can reduce or eliminate jetting regardless of amount of elasticity of polymer melt.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 금형가공 심포지엄
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• pp.125-131
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• 2002

Surface defects in injection molded parts are due to the unsteady flow of polymer melt which are related to the geometries of cavity and gate, the operational conditions of injection and the rheological properties of polymer. In this study we have examined jetting phenomena in injection molding process for three kinds of PCs which have different molecular weight and structure, PBT and PC/ABS alloy with several injection speeds. We have used various cavity shapes that are tensile, flexural and impact test specimens with various gate and cavity thicknesses. Through this study we have observed that the formation of surface defect associated with jetting during filling stage in injection molding is strongly related to die swell. This means that the jetting is strongly affected by the elastic property rather than the viscous property in viscoelastic characteristics of molten polymer. Large die swell would eliminate jetting however, the retardation of die swell would stimulate jetting. In the point of mold design, reducing the thickness ratio of cavity to gate can reduce or eliminate jetting and associated surface defects regardless of magnitude of elastic property. It also enlarges process window that can produce steady flow of polymer melt in injection molding.

• 한국식품과학회지
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• 제20권6호
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• pp.850-855
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• 1988

탈지처리한 전분시료 및 탈지후 1% palmitic acid를 첨가한 시료를 제조하여 이들의 리올로지 특성을 생전분과 비교 검토하였다. 3-7%의 전분호화액은 항복응력이 존재하는 의가소성을 나타내었으며 탈지처리에 의해 항복응력이 감소하였다. 점조도지수의 대수값과 농도의 관계는 생전분에서 단일기울기를 갖는 직선관계를 보였으나 탈지전분 및 지방산 첨가전분에서는 전분농도 5%에서 기울기가 서로 다른 두개의 직선 관계를 나타내었다. 7% 전분 시료액의 활성화에너지는 3.14-4.76 kcal/gmol 이었으며 탈지처리로 활성화 에너지는 다소 증가하였다. 또 모든 시료는 4% 이상 농도에서 hysteresis현상을 나타내었으며, 탈지처리로 humping현상을 나타내었으며 시간의존성도 증가하는 경향을 보였다.