• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.203-211
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• 2009

In flows with deformation rates larger than the inverse Rouse time of the polymer chain, chains are stretched and their confining tubes become increasingly anisotropic. The pressures exerted by a polymer chain on the walls of an anisotropic confinement are anisotropic and limit chain stretch. In the Molecular Stress Function (MSF) model, chain stretch is balanced by an interchain pressure term, which is inverse proportional to the $3^{rd}$ power of the tube diameter and is characterized by a tube diameter relaxation time. We show that the tube diameter relaxation time is equal to 3 times the Rouse time in the limit of small chain stretch. At larger deformations, we argue that chain stretch is balanced by two restoring tensions with weights of 1/3 in the longitudinal direction of the tube (due to a linear spring force) and 2/3 in the lateral direction (due to the nonlinear interchain pressure), both of which are characterized by the Rouse time. This approach is shown to be in quantitative agreement with transient and steady-state elongational viscosity data of two monodisperse polystyrene melts without using any nonlinear parameter, i.e. solely based on the linear-viscoelastic characterization of the melts. The same approach is extended to model experimental data of four styrene-butadiene random copolymer melts in shear flow. Thus for monodisperse linear polymer melts, for the first time a constitutive equation is presented which allows quantitative modeling of nonlinear extension and shear rheology on the basis of linear-viscoelastic data alone.

• Tribology and Lubricants
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• v.14 no.1
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• pp.85-93
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• 1998

The Bair & Winer's limiting shear stress rheological model is incorporated into the Reynolds equation to successfully predict the traction and film thickness for an isothermal line contact using the primary rheological properties. The modified WLF viscosity model and Barus viscosity model are also adapted for the realistic prediction of EHD tractional behavior. The influences of the limiting shear stress and slide-roll ratio on the pressure spike, film thickness, distribution of shear stress and nonlinear variation of traction are examined. A good agreement between the disc machine experiments and numerical traction prediction has been established. The film thickness due to non-Newtonian effects does not deviate significantly from the fdm thicknesss with Newtonian lubricant.

• Korea-Australia Rheology Journal
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• v.15 no.1
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• pp.19-25
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• 2003

Since the microstructure of functional thin films depends on the dispersion characteristics of dense slurry, it is important to control the agglomerative nature of slurries under processing. The present authors have been discussing the model prediction of agglomerative nature and local rate of agglomeration in dense suspensions. The experiments have been peformed under shear flow using the nearly spherical and oblate type graphite particles. In this study, the experiment has been conducted using water and glycerol as dispersion media. Stress control type rheometer was used to measure the slurry rheology. Local agglomeration of graphite particles has been predicted by using Usui's model. The experimental results show that both the shape and slurry processing method affect on the local dispersion condition. The agglomeration formed by oblate type graphite particles seems to be more difficult to break up than that of spherical particles.

• Korea-Australia Rheology Journal
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• v.20 no.4
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• pp.227-233
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• 2008

High impact polystyrene (HIPS)/organoclay nanocomposites via in situ polymerization were synthesized and their rheological properties were investigated. For the study, two types of organoclays were used: a commercially available organoclay, Cloisite 10A (C10A), and a laboratory-prepared organoclay having a reactant group, vinylclay (ODVC). The X-ray diffraction and transmission electron microscopy experiments revealed that the HIPS/ODVC nanocomposite achieved an exfoliated structure, whereas the HIPS/C10A nanocomposite achieved an intercalated structure. In the small-amplitude oscillatory shear experiments, both storage modulus and complex viscosity increased with increasing organoclay. A pronounced effect of the organoclay content was observed, resulting in larger storage modulus and stronger yield behavior in the low frequency region when compared to neat HIPS. The crossover frequencies associated with the inverse of a longest relaxation time decreased as the organoclay content increased. Over a certain value of ODVC content, a change of pattern in rheological properties could be found, indicating a solid-like response with storage modulus greater than loss modulus at all frequencies.

• Korea-Australia Rheology Journal
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• v.19 no.2
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• pp.81-88
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• 2007

Blends of collagen dispersion (COL) with poly(vinyl alcohol) (PVA) in different weight ratios were investigated by oscillatory rheometry, Fourier transform-infrared spectroscopy and scanning electron microscopy. It was found that even with 80% of PVA, the COL/PVA blends behaved more like collagen dispersion than pure PVA solution in the dynamic thermal and frequency processing, for instance, a dominant elastic appearance (G'>G"), a similar shear thinning behavior and the thermal denaturation below $40^{\circ}C$. However, influence on the blend behaviour by PVA was noticeable, for instance, an increase of dynamic denaturation temperature, the decreasing intensity of amide I, II and III bands as well as the diminishing irregular pores on the surface of blends. The interaction between collagen and PVA could be observed, especially at the regions with low content or high content of PVA.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.181-194
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• 2013

Landslides are known as gravitational mass movements that can carry the flow materials ranging in size from clay to boulders. The various types of landslides are differentiated by rate and depositional features. Indeed, flow characteristics are observed from very slow-moving landslides (e.g., mud slide and mud flow) to very fast-moving landslides (e.g., debris avalanches and debris flows). From a geomechanical point of view, shear-rate-dependent shear strength should be examined in landslides. This paper presents the design of advanced ring-shear apparatus to measure the undrained shear strength of debris flow materials in Korea. As updated from conventional ring-shear apparatus, this apparatus can evaluate the shear strength under different conditions of saturation, drainage and consolidation. We also briefly discussed on the ring shear apparatus for enforcing sealing and rotation control. For the materials with sands and gravels, an undrained ring-shear test was carried out simulating the undrained loading process that takes place in the pre-existing slip surface. We have observed typical evolution of shear strength that found in the literature. This paper presents the research background and expected results from the ring-shear apparatus. At high shear speed, a temporary liquefaction and grain-crushing occurred in the sliding zone may take an important role in the long-runout landslide motion. Strength in rheology can be also determined in post-failure dynamics using ring-shear apparatus and be utilized in debris flow mobility.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.10
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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.

• Advanced Composite Materials
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• v.17 no.3
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• pp.191-214
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• 2008

Polypropylene/layered silicate nanocomposites containing maleic anhydride grafted polypropylene were prepared by melt compounding and their rheological behavior was investigated in shear flow. Transient and steady shear flows were simulated numerically by using the K-BKZ integral constitutive equation along with experimentally determined damping functions under dynamic oscillatory and step strain shear flows. Nonlinear shear responses were predicted with the K-BKZ constitutive equation using two different damping functions such as the Wagner and PSM models. It was observed that PP-g-MAH compatibilized PP/layered silicate nanocomposites have stronger and earlier shear thinning and higher steady shear viscosity than pure PP resin or uncompatibilized nanocomposites at low shear rate regions. Strong damping behavior of the PP/layered silicate nanocomposite was predicted under large step shear strain and considered as a result of the strain-induced orientation of the organoclay in the shear flow. Steady shear viscosity of the pure PP and uncompatibilized nanocomposite predicted by the K-BKZ model was in good agreement with the experimental results at all shear rate regions. However, the model was inadequate to predict the steady shear viscosity of PP-g-MAH compatibilized nanocomposites quantitatively because the K-BKZ model overestimates strain-softening damping behavior for PP/layered silicate nanocomposites.

• Korea-Australia Rheology Journal
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• v.17 no.1
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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.