• Korea-Australia Rheology Journal
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• 제18권4호
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• pp.199-207
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• 2006

Measurements by Luap et al. (2005) of elongational viscosity and birefringence of two nearly monodisperse polystyrene melts with molar masses $M_{w}$ of $206,000g{\cdot}mol^{-1}$ (PS206k) and $465,000g{\cdot}mol^{-1}$ (PS465k) respectively are reconsidered. At higher elongational stresses, the samples showed clearly deviations from the stress optical rule (SOR). The elongational viscosity data of both melts can be modeled quantitatively by the MSF model of Wagner et al. (2005), which is based on the assumption of a strain-dependent tube diameter and the interchain pressure term of Marrucci and Ianniruberto (2004). The only nonlinear parameter of the model, the tube diameter relaxation time, scales with $M_{w}^{2}$. In order to get agreement with the birefringence data, finite chain extensibility effects are taken into account by use of the $Pad\'{e}$ approximation of the inverse Langevin function, and the interchain pressure term is modified accordingly. Due to a selfregulating limitation of chain stretch by the FENE interchain pressure term, the transient elongational viscosity shows a small dependence on finite extensibility only, while the predicted steady-state elongational viscosity is not affected by non-Gaussian effects in agreement with experimental evidence. However, deviations from the SOR are described quantitatively by the MSF model by taking into account finite chain extensibility, and within the experimental window investigated, deviations from the SOR are predicted to be strain rate, temperature, and molar mass independent for the two nearly monodisperse polystyrene melts in good agreement with experimental data.

• 한국식품영양과학회지
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• 제44권9호
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• pp.1407-1413
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• 2015

본 연구는 '고운' 품종으로 제조한 감자가루 분산액의 농도(3, 4, 5, 6, 7%, w/w)에 따른 유변학적 및 페이스팅 특성에 대하여 평가하였다. 감자가루 분산액은 전단담화 거동(n=0.41~0.55)을 나타냈으며, 감자가루 농도가 증가함에 따라 점조도 지수(n), 겉보기 점도(${\eta}_{a,100}$), Casson 항복응력(${\sigma}_{oc}$)값이 증가하는 경향을 나타내었다. 또한 동적 점탄 특성 측정 결과에 의하면 감자가루 분산액은 약한 겔과 같은 거동을 보여주었으며 G'과 G" 값들은 감자가루 농도와 진동수(${\omega}$)가 증가함에 따라 증가하는 경향을 나타내었다. Cox-Merz 중첩원리는 감자가루 분산액에 잘 적용되지 않았다. RVA에 의한 페이스팅 특성은 감자가루 농도가 증가할수록 peak viscosity, trough viscosity, final viscosity, set back viscosity, break down viscosity 값이 유의적으로 증가하였다.

• Journal of Pharmaceutical Investigation
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• 제29권4호
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• pp.295-307
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• 1999

Using a Rheometries Fluids Spectrometer (RFS II), the dynamic viscoelastic properties of aqueous poly(ethylene oxide) (PEO) solutions in small amplitude oscillatory shear flow fields have been measured over a wide range of angular frequencies. The angular frequency dependence of the storage and loss moduli at various molecular weights and concentrations was reported in detail, and the result was interpreted using the concept of a Deborah number De. In addition, the experimentally determined critical angular frequency at which the storage and loss moduli become equivalent was compared with the calculated characteristic time (or its inverse value), and their physical significance in analyzing the dynamic viscoelastic behavior was discussed. Finally, the relationship between steady shear flow and dynamic viscoelstic properties was examined by evaluating the applicability of some proposed models that describe the correlations between steady flow viscosity and dynamic viscosity, dynamic fluidity, and complex viscosity. Main results obtained from this study can be summarized as follows: (1) At lower angular frequencies where De<1, the loss modulus is larger than the storage modulus. However, such a relation between the two moduli is reversed at higher angular frequencies where De>l, indicating that the elastic behavior becomes dominant to the viscous behavior at frequency range higher than a critical angular frequency. (2) A critical angular frequency is decreased as an increase in concentration and/or molecular weight. Both the viscous and elastic properties show a stronger dependence on the molecular weight than on the concentration. (3) A characteristic time is increased with increasing concentration and/or molecular weight. The power-law relationship holds between the inverse value of a characteristic time and a critical angular frequency. (4) Among the previously proposed models, the Cox-Merz rule implying the equivalence between the steady flow viscosity and the magnitude of the complex viscosity has the best validity. The Osaki relation can be regarded to some extent as a suitable model. However, the DeWitt, Pao and HusebyBlyler models are not applicable to describe the correlations between steady shear flow and dynamic viscoelastic properties.

• 오토저널
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• 제8권2호
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• pp.43-50
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• 1986

Numerical analysis has been made on the dynamic behavior of an elastically supported beam subjected to an axial force and solid viscosity when the frequency of external force passes through the first critical frequency of the beam. Within the Euler-Bernoulli beam theory the solutions are obtained by using finite Fourier sine transform and Laplace transformation methods with respect to space and time variables. Integrations involved in the theoretical results are carried out by Simpson's numerical integration rule. The result shows that the maximum value of the dynamic deflection are much affected by the value of a solid viscosity, an axial force, an elastic constant and ratio of .omega.$_{max}$/.omega.$_{1}$.

• 한국정밀공학회지
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• 제18권9호
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• pp.156-164
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• 2001

Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum alloy has been studied. Two-phase fluid flow model to investigate the velocity field and temperature distribution is proposed. The proposed mathematical model is applied to the die shape of the two types. To calculate the velocity and temperature fields during rheology forming process, the earth governing equation correspondent to the liquid and solid region are adapted. Therefore, each numerical models considering the solid and liquid region existing within the semi-solid material have been developed to predict the deflect of rheology forming gnarls. The Arbitrary Boundary Maker And Cell (ABMAC) method is employed to solve the two-phase flow model of the Navier-Stokes equation. Theoretical model on the basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on the liquid and solid viscosity. The liquid viscosity is pure liquid state value, however solid viscosity is considered as a function of the shear rate, solid fraction and power law curves.

• 대한기계학회논문집A
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• 제26권10호
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• pp.1971-1981
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• 2002

Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum alloy has been studied. Two-phase flow model to investigate the velocity field and temperature distribution is proposed. The proposed mathematical model is applied to the die shape of the two types. To calculate the velocities and temperature fields during rheology forming process, the each governing equations correspondent to the liquid and solid region are adapted. Therefore, each numerical model considering the solid and liquid coexisting region within the semi-solid material have been developed to predict the defects of rheology forming parts. The Arbitrary Boundary Maker And Cell(ABMAC) method is employed to solve the two-Phase flow model of the Navier-Stokes equation. Theoretical model basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on using the liquid and solid viscosity. The Liquid viscosity is pure liquid state value, however solid viscosity is considered as a function of the shear rate, solid fraction and power law curves.

• 공업화학
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• 제10권8호
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• pp.1175-1179
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• 1999

반도체 봉지재용 epoxy molding compound(EMC)에는 고함량의 충전제가 함유되어 있어 충전제의 함량이 유변학적 거동에 큰 영향을 미친다. 본 연구에서는 반도체 봉지재용 EMC의 점도거동을 충전제 함량과 주파수(frequency)의 변화에 따라 조사하였다. 또한 주파수변화에 따른 점도거동을 전단율(shear rate)의 함수로 변환하기 위해 Cox-Merz 식과 modified Cox-Merz 식을 적용해 보았다. 이 결과 고함량에서 전단박화현상(shear thinning)과 항복강도(yield stress)가 관찰되었으며 전단율의 함수로의 변환은 Cox-Merz식을 적용하였을 때는 고종도에서 변형율 변화에 따른 점도값 차이 때문에 적용될 수 없었다. Modified Cox-Merz식을 적용하였을 때는 고농도/고변형율에서는 측정장치의 한계 때문에 오차를 보이기는 하지만 각 변형율에 따른 점도값들이 한 개의 마스터곡선으로 일치되는 경향을 보였다.

• Korea-Australia Rheology Journal
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• 제17권1호
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• pp.1-7
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• 2005

Acrylonitrile-Butadiene-Styrene (ABS), polycarbonate (PC) and their alloys are an important class of engineering thermoplastics that are widely used for automotive industry, computer and equipment housings. For the process of recycling mixtures of ABS and PC, it is desirable to know how sensitive the blend properties are to changes in compositions. It was for this reason that blends of virgin ABS and virgin PC at five different compositions, namely, $15\%,\;30\%,\;50\%,\;70%$ and $85\%$ by weight of ABS were prepared and characterised by rheological and mechanical measurements. Rheological properties of these blends in steady, oscillatory and transient step shear and mechanical properties, namely, tensile strength, elongation-at-break and Izod impact strength are reported. The results show that PC behaves in a relatively Newtonian manner, but ABS exhibits significant shear thinning. The ABS-rich blends show a trend that is similar to that of ABS, while PC-rich blends, namely $0\%$ and $15\%$, exhibit a nearly Newtonian behaviour. However, at a fixed shear rate or frequency, the steady shear or the dynamic viscosity varied respectively in a non-mono-tonic manner with composition. Except for $15\%$ blend, the viscosities of other blends fall into a narrow band indicating a wide-operation window of varying blend ratio. The blends exhibited a lower viscosity than either of the two pure components. The other noticeable feature was that the blends at $70\%$ and $85\%$ ABS content had a higher G' than pure ABS, indicating an enhancement of elastic effect. The tensile yield strength of the blends followed the 'rule of mixtures' showing a decreasing value with the increase of ABS content in PC. However, the elongation-at-break and the impact strength did not appear to obey this 'rule of mixtures,' which suggests that morphology of the blends also plays a significant role in determining the properties. Indeed, scanning electron micrographs of the fracture surfaces of the different blends validate this hypothesis, and the $15\%$ blend is seen to have the most distinct morphology and correspondingly different behaviour and properties.

• 대한토목학회논문집
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• 제13권2호
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• pp.61-71
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• 1993

충돌이나 폭파시 발생하는 기계적 에너지나 화학적 에너지는 응력파의 형태로 매체를 통과하게 되며, 매체의 자유면과 절리면을 따라 반사와 굴절을 거듭하는 매우 복잡한 과정을 거치게 된다. 본 연구에서는 재료특성을 달리하는 층을 통과하는 소성응력파의 전파과정을 압력 부종속 모델인 Von-Mises 모델을 사용하여 연구하였다. 응력파의 전파과정을 연구하기 위한 지배 방정식(governing equation)으로서는 물체에 종속되어 있는 라그란지안 좌표계(lagrangian coordinate system)로 표현된 운동량과 질량보존(conservation of momentum and mass)법칙식을 사용하였으며 또한 충격전면(shock front)에 연속성을 부여하기 위해 인공점성(artificial viscosity)을 운동량 보존식에 첨가하였다. 주요 방정식을 풀기 위한 수치해석법으로는 시간과 공간 좌표계로 구성된 유한차분법(finite difference method)을 사용하였으며 소성변형률을 구하기 위한 소성이론으로서는 associated normality flow rule을 사용하였다.

• 대한토목학회논문집
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• 제12권2호
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• pp.21-33
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• 1992

충격하중을 받는 구조물은 초고압에서 부터 저압까지 다양한 압력을 짧은 시간에 경험하게 된다. 따라서 이들 구조물을 해석하기 위해서는 실제 물체의 재료특성을 표현할 수 있는 구성 법칙(constitutive law)이 필요하게 된다. 본 연구에서는 압력 부종속모델(pressure independent model)인 Von-Mises 모델과 압력 종속모델(pressure dependent model)인 Drucker-Prager 모델을 사용하여 충격과 폭발 현상시 발생하는 응력파의 전파과정(propagation process)을 재료특성에 따라 비교 분석하였다. 응력파의 전파과정을 연구하기 위한 지배 방정식(governing equation)으로서는 물체에 종속되어 있는 라그란지안 좌표계(lagrangian coordinate system)로 표현된 운동량과 질량보존(conservation of momentum and mass)법칙을 사용하였으며 또한 충격전면(shock front)에 연속성을 부여하기 위해 인공점성(artificial viscosity)을 운동량 보존식에 첨가하였다. 주요 방정식을 풀기 위한 수치해석법으로는 시간과 공간 좌표계로 구성된 유한차분법(finite difference method)을 사용하였으며 소성변형률을 구하기 위한 소성이론으로서는 Associated normality flow rule을 사용하였다.