• Polymer(Korea)
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• v.26 no.1
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• pp.88-97
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• 2002

The effect of aminosiloxane modifier on the chemorheological properties of ortho-cresol novolac epoxy/phenol novelac/triphnylphosphine resin system was investigated aat different isothermal curing temperatures. By adding the aminosiloxane to the resin system, not only conversion rate and conversion were increased but also glass transition temperature was promoted. Critical conversion and gelation time obtained at the crossover point between storage and loss moduli were reduced and thus the viscosity was increased by the aminosiloxane. $C_1$ and $C_2$ in the WLF equation calculated from the glass transition temperature as a function of conversion and measured viscosity were found to vary with the curing temperature. By applying the change of glass transition temperature with conversion, $C_1$ and $C_2$ to WLF equation, it was possible to predict accurately the viscosity change with isothermal curing reaction.

• 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.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.60-65
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• 2001

To simulate the real molding conditions, the effects of phase change and compressibility of the resin were considered in the present investigation. A modified Cross model with either an Arrhenius-type or WLF-type functional form was used for modeling viscosity of the resin. A double-domain Tait equation of state was employed to describe the compressibility of the resin during molding. The energy balance equation including latent-heat dissipation fur semi-crystalline materials was solved in order to predict the solidified layer and temperature profile. Injection molding experiments were carried out using polypropylene(PP) in the present study. Based on the comparison between experiments and simulations, it was found out the predicted pressure distributions and melt front propagations were accurate. Thus it was concluded that the program developed in this study was proved to be useful in simulations of injection molding process.

• Korean Journal of Food Science and Technology
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• v.24 no.2
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• pp.165-170
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• 1992

The creep behavior of gels made with $30{\sim}45%$ gelatinized rice starch was measured over a wide range of temperature. Compressive creep curves of rice starch gels conformed to a six element mechanical model consisting of one Hookean, two Voigt and one Newtonian component. The creep compliance of gels decreased with increasing starch concentrations. Among viscoelastic constants of the mechanical model, elastic modulus was mainly influenced by the change of starch concentrations. The concentration-invariant compliance curve was obtained by reduction to 38% using reduction parameter $a_{c}$. The creep compliance curves of 45% starch gels increased with temperature, which indicated that rice starch gels became softer and less rigid with increasing temperature. When the compliance at $20^{\circ}C$ was set as a reference curve, creep compliance data for 45% gels at various temperature could be superimposed as a continuous smooth curve. The apparent activation energies of 45% rice starch gels calculated by the modified WLF equation were not intrinsic, but decreased as temperature increased.