• Elastomers and Composites
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• v.46 no.1
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• pp.54-59
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• 2011

One of the viscoelastic flow behaviors during profile extrusion is the swelling of extrudate. In this study, die swell of rubber compound in the capillary die have been investigated through experiment and computer simulation. Simplified viscoelastic model and non-linear differential viscoelastic model such as PTT model have been used in the computer simulation. The simulation results have been compared with experimental data. Experiment and simulation have been performed using fluidity tester and commercial CFD code, Polyflow respectively. Die swells predicted by two models showed good agreement with experimental results. Pressure and velocity distribution, and circulation flow at the corner of reservoir have been well predicted by PTT model. Simplified viscoelastic model can not predict circulation flow at the corner of reservoir. However this model has an advantage in computation time compare with full viscoelastic model, PTT model.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.3
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• pp.43-48
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• 2022

In this study, simulation method was developed to improve the accuracy of the warpage simulation based on the equivalent anisotropic viscoelastic model. First, a package with copper traces and bumps was modeled to implement anisotropic viscoelastic behavior. Then, equivalent anisotropic viscoelastic properties and thermal expansion coefficient for the bump region were derived through the representative volume element model. A thermal cycle of 0 to 125 degrees was applied to the package based on the derived mechanical properties, and the warpage according to the thermal cycle was simulated. To verify the simulation results, the actual package was manufactured, and the warpage with respect to the thermal cycle was measured through shadow moiré interferometer. As a result, by applying the equivalent anisotropic viscoelastic model, it was possible to calculate the warpage of the package within 5 ㎛ error and predict the shape of the warpage.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.1
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• pp.35-41
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• 1986

A hybrid modelling technique of a soil-structure system on viscoelastic soil medium is studied in this paper. The hybrid model consists of a near-field and a far-field with their common interface passing through the soil region at some distance from the base of the structure. It makes use of frequency-dependent impedances so as to represent the semi-infinite far-field. The far-field impedances are formulate including the radiation damping characteristics as well as the viscoelastic properties of the soil medium. The verification of the method has been carried out using a rigid circular plate on a viscoelastic half-space. The impedances obtained by the method are compared with the theoretical values. Example analyses have been performed for a tall chimney and the results have been compared with those obtained by other methods which are frequently used.

• Computational Structural Engineering
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• v.9 no.1
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• pp.85-91
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• 1996

The focus of the present work is on the computation of the stress intensity factor for the crack at the elastic-viscoelastic bimaterial interface. First, the stress intensity factor for an interface crack in dissimilar elastic and viscoelastic materials is dervied by applying the correspondence principle to associated elastic expression. Then the time-domain boundary element analysis is performed to calculate the stress intensity factor. Numerical results show that the proposed method is very useful for the analysis of the interface crack in elastic and viscoelastic materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2072-2078
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• 2003

In this paper, the boundary element analysis of viscoelastic strain energy release rate G(t) for the cracked linear viscoelastic solids has been attempted. This study proposes the G(t) equation and the calculating method of G(t) by time-domain boundary element analysis for the viscoelastic solids. The G(t) is defined as the derivative of the viscoelastic potential energy II(t) with respect to crack length a. Two example problems are presented to show the applicability of the proposed method to the analysis of the cracked linear viscoelastic solids. Numerical results of example problems show the accuracy and effectiveness of the proposed method.

• The Korean Journal of Rheology
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• v.11 no.1
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• pp.9-17
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• 1999

Viscoelastic characteristics of cured phenolic resin/carbon fiber composite materials were investigated through glass transition and degradation reaction processes in the high temperature region up to $400^{\circ}C$. A typical glass transition of the cross-linked thermoset polymer was followed by irreversible degradation reactions, which were exhibited by the increasing storage modulus and loss modulus peak. A degradation master curve was constructed by using the vertical and horizontal shift factors, both of which complied well with the Arrhenius equation in light of the kinetic expression of degradation rate constants. Using an analogy to the Havriliak-Negami equation in dielectric relaxation phenomena, a viscoelastic modeling methodology was developed to characterize the frequency- and temperature-dependent complex moduli of the degrading thermoset polymer composite systems. The temperature-dependent relaxation time of the degrading composites was determined in a continuous fashion and showed a minimum relaxation time between the glass transition and degradation reaction regions. The capability of the developed modeling methodology was demonstrated by describing the complex behavior of the viscoelastic complex moduli of reacting phenolic resin composite systems.

• Computational Structural Engineering
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• v.6 no.1
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• pp.127-135
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• 1993

This paper summarizes a study on the application of viscoelastic dampers as an energy dissipation device in the frame structure. It can be concluded that, even at high temperatures, the viscoelastically damped structure can achieve a significant reduction of structural response as compared to the case with no dampers added. Empirical formulae for estimating the dynamic properties of the viscoelastic damper are established based on the regression analysis using data obtained from component tests of the damper. The structural damping with added dampers can be satisfactorily estimated by the modal strain energy method and the derived empirical formulae. Numerical simulations using conventional modal analysis methods are also carried out to predict the dynamic response of viscoelastically damped structures under seismic excitations. Comparison between numerical simulations and test results shows very good agreement. Based on the above studies, a design procedure for viscoelastically damped structures is present . This design procedure fits naturally into the conventional structural design flow-chart by including damping ratio an additional design parameter.

• Elastomers and Composites
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• v.41 no.4
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• pp.223-230
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• 2006

Rubber compounds have a high viscoelastic property. One of the viscoelastic behaviors during profile extrusion is the swelling of extrudate, and the amount of swelling varies with operational conditions in extrusion. It is well recognized that the elastic portion in the viscoelastic property plays an important role in the extrudate swell. In this study computer simulation of the die swell at the capillary die for several rubber compounds has been performed using commercial CFD code, Polyflow. A non-linear differential viscoelastic model, Phan-Thien-Tanner (PTT) model, was used in the computer simulation. Non-isothermal behavior was considered in the calculation. Distribution of pressure, velocity and temperature in the reservoir and capillary die, and extrudate profiles were predicted through the simulation. The amount of the die swell fur the different rubber compounds was investigated for various flow rates and three types of length to diameter of the capillary die. It is concluded that the PTT model successfully represented viscoelastic behavior of rubber compounds.

• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.57-61
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• 2002

점탄성학은 고분자물과 같이 기계적 성질이 시간에 따라 변하는 물질의 응력과 변형해석에 관한 학문이다. 이에 대한 이전의 문헌들은 균일변형시의 조성식에 대한 주제를 주로 다룬 반면, 경계조건 문제(boundary value problem)로서의 불균일 변형해석에 대한 논의가 부족한 편이다. 본 논문에서는 불균일 변형해석에 유용한 상응원리 (correspondence theorem)[1]을 보이론(beam theory)에 적용하는 경우, 적용가능조건을 유도하는 한편 상응원리를 적용 예를 들어 설명하였다. (중략)

• The Korean Journal of Rheology
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• v.3 no.2
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• pp.148-155
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• 1991

본 연구에서는 빗모양이 고분자분자가 희석용액상태에 있을때의 점탄성 거동을 이 론적으로 해석하였다. 수치해석 방법으로는 Osaki 등이 제안한 방법을 따랐다. 고분자분자 의 이완시간은 Eigenvalue equation을 풀어서 구하였으며 고분자분자와 용매간의 역학은 Zimm-Kilb model을 적용하였다. 본 연구에서는 분지쇄의 길이가 다른 경우 이들이 분자쇄 거동에 미치는 영향을 고찰하였으며 높은 진동수에서의 현상을 해석하였다.