• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.6
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• pp.104-112
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• 2014

Generally, numerical approaches of evaluation for vehicle seat comfort have been studied without considering time-dependent characteristics and the only seating moment have been considered in seat design. However, the comfort not only at the seating moment but also in the long-term should be evaluated because the passengers are sitting repeatedly on the seat to drive the vehicle for hours. So, the aim of this paper is to carry out a quantitative evaluation of the time-dependent mechanical characteristics of seat foams and to suggest a process for predicting the viscoelastic deformation of seat foam in response to long-term driving. To characterize the seat materials, uniaxial compression and tension tests were carried out for the seat foam and stress relaxation tests were performed for evaluating the viscoelastic behavior of the seat foam. A unit solid element model was used to verify the reliability of the material model with respect to the compression behavior of the seat foam. It is not straightforward to evaluate the time-dependent compression of foams using the explicit solver because the viscoelastic material model is limited. To use the explicit solver, the material model must be modified using stress-degradation data. Normalized stress relaxation moduli were added to the stress-strain curves obtained under static conditions to achieve a time-dependent set of stress-strain relations that were compatible with the implicit solver. There was good agreement between the analysis results and experimental data.

• Textile Coloration and Finishing
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• v.11 no.5
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• pp.44-54
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• 1999

Poly(ethylene 2,6-naphthalate), PEN, is a relatively well-known polymer used for engineering purposes. Naphthalene ring provides rigidity to the polymer backbone, thus, it elevated the glass transition temperature and enhanced mechanical properties. The structure and properties of PEN affect a processing conditions severely, and the high-thermal stability have been had a poor thermal processibility. Hence, the basic mechanism of solvent drawing, is very much the same as that of thermal drawing from glassy state since both involve the inducement of segmental mobility. The former achieves the goal by use of chemical energy, and the latter does so by use of thermal energy. Generally, the sorption of the solvent by the polymer has a plasticizing effect, and leads to a lowering of the glass transition temperature, $T_g$. In this paper, the dynamic viscoelasticity behavior in liquid-drawing process of an unoriented amorphous PEN films were investigated using Rheovibron. The results are as follows ： (1) For the drawing in silicone oil, the drawing below $T_g$. had $\alpha{2}$-dispersion due to an inhomogeneous taut structure. (2) For the drawing in water, the inhomogeneous taut structure reduced by the effect of plasticization even below $T_g$. (3) For the drawing in butanol, the only aliphatic segment in PEN have some molecular mobility but the mobility of the aromatic segment having naphthalene ring is nearly impossible. (4) For the drawing in dioxane/water mixing solvent, the solvent effect is complementary each other and accordingly the entire molecular conformation have stable state. (5) For the drawing in dioxane/butanol mixing solvent, the inhomogeneity of the taut structure and the aromatic segment increase with increasing the temperature and this tendencies correspond with that of the draw ratio.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.2
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• pp.83-90
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• 2010

The windshield wiper consists of 4 parts: a blade, an arm, a linkage and a motor. The wiper blade makes contact with the windshield and is designed to be operated normally at an angle of 30~50 degrees to the front glass. If the contact pressure between the wiper blade and windshield surface is too high, noise and wear of the rubber will result. On the other hand, if the contact pressure is too low, the performance will do badly, since foreign substances such as dust and stains will not be removed well. The pressure and friction of the wiper blade has a great influence on its effectiveness in cleaning the front window. This is due to the contact of the rubber with the window. This paper presents the dynamic analysis method to estimate the performance of the flat type blade of the wiper system. The blade has a nonlinear characteristic since the rubber is an incompressible hyper-elastic and visco-elastic material. Thus, Structural dynamic analysis using a complex contact model for the blade is performed to find the characteristics of the blade. The flexible multi-body dynamic model is verified by the comparison between test and analysis result. Also, the optimization using the central composite design table is performed.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.4
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• pp.121-126
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• 2010

The automotive weather strip has functions of isolating of water, dust, noise and vibration from outside. To achieve good sealing performance, weather strip should be designed to have the high contact force and wide contact area. However, these design causes excessive permanent deformation of weather strip. The causes of permanent deformation is generally explained to be the chemical material detrioration and physical variation and cyclic loading, etc. This paper introduces a numerical method to predict the permanent deformation using the time dependent viscoelastic model which is represented by Prony series in ABAQUS. Uniaxial tension and creep tests were conducted to obtain the material data. And the lab. test for the permanent deformation was accelerated during shorter time, 300 hours. The permanent deformation of weather strip was successfully predicted under the different loading conditions and different section shapes using the suggested numerical process.

• Korean Journal of Food Science and Technology
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• v.35 no.2
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• pp.188-194
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• 2003

천마식품가공시 기초자료로 활용될 수 있는 천마 추출농축액의 리올로지 특성을 조사하였다. 천마의 열수 및 50% 에탄올 추출물운 각각 5, 10, 15, 및 20 Brix와 10, 20, 30, 40 및 50 Brix로 농축하여 제조하였다. 열수 및 50% 에탄올 농축액의 정상유동특성과 동적점탄성을 조사하였다. Power law model로 구한 n에 의하면 모든 열수 농축액들은 전형적인 의가소성$(n=0.484{\sim}0.802)$유체의 흐름특성을 보였고, 50% 에탄올 농축액들은 뉴튼유체$(n=0.875{\sim}1.078)$에 가까운 흐름특성을 나타내었다. 열수 및 50% 에탄올 농축액의 ${\eta}_{app}$는 온도가 증가함에 따라 감소하는 경향을 나타내었다. Herschel-Bulkley model에 의한 열수 및 50% 에탄올 농축액의 C는 각각 $0.030{\sim}1.255$ Pa와 $0.007{\sim}0.065$ Pa이었다. ${\eta}_{app}$에 대한 온도 및 농도의 영향은 arrhenius식으로 해석하였다. 열수 및 50% 에탄올 농축액의 $E_a$는 농도가 증가함에 따라 각각 $3.340{\sim}4.620{\times}10^3\;J/mol{\cdot}kg$과 $1.6289{\sim}18.6699{\times}10^3\;J/mol{\cdot}kg$의 범위로 나타났다. 진동수(angular frequency, ${\omega}$)가 증가할수록 저장탄성률(storage modulus, G#)과 손실탄성률(loss modulus, G@)은 일반적으로 증가하는 경향을 나타냈다. 50% 에탄올 농축액의 경우 모든 진동수에서 G#이 G@보다 높게 나타나 전형적인 저분자용액의 흐름특성을 보였다. 그러나 열수농축액의 경우 G@이 G#보다 높았고 0.5 rad/sec에서 교차점을 형성하였으며 전형적인 고분자 용액의 흐름특성을 나타내었다.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.5
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• pp.596-604
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• 2016

In this study, we used a stochastic approach for guaranteeing the reliability and robustness of the performance with regard to the design of polymer components, while taking into consideration the degradation properties and operating conditions in automobiles. Creep and tensile tests were performed for obtaining degradation properties. The Prony series, which described the viscoelastic models, were calculated to use the creep data by the Maxwell fluid model. We obtained the stress data from the frequency response analysis of the polymer components while considering the degradation properties. Limit state functions are generated by using these data. Reliability assessments are conducted under the variation of the degradation properties and area of frequency at peak response. For this study, the input parameters are assumed to be a normal distribution, and the reliability under the yield stress criteria is evaluated by using the Monte Carlo Simulation. As a result, the reliabilities, according to the three types of polymer materials in automotive components, are compared to each other and suggested the applicable possibility of polymeric materials in automobiles.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.2
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• pp.51-57
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• 2021

This paper analyzed the effects of the concentration of nano-silica particles contained in epoxy resin on the thermomechanical properties of the composite materials. The 12nm sized nanoparticles were mixed with epoxy polymer by 5 different weight ratios for the test samples. The glass transition temperature, stress relaxation, and thermal expansion behaviors were measured using dymanic mechanical analyzer (DMA) and thermomechanical analyzer (TMA). It was shown that the nano particle mixing ratios had significant influences on the viscoelastic behaviors of the materials. As the content of the silica particles was increased, the elastic modulus was also increased, while the glass transition temperatures were decreased. Fourier Transform Infrared Spectroscopy (FTIR) results played an important role in determining the causes of the property changes by the filler contents in terms of the molecular structures, enabling the interpretations on the material behaviors based on the chemical structure changes.

• Composites Research
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• v.37 no.3
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• pp.155-161
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• 2024

Boron nitride nanotubes and carbon nanotubes are the most representative one-dimensional nanostructures, and have received great attention as reinforcement for multifunctional composites for their excellent physical properties. The two nanotubes have similar excellent mechanical stiffness, strength, and heat conduction properties. Therefore, the reinforcing effect of these two nanotubes is greatly influenced by the properties of their interface with the polymer matrix. In this paper, recent comparative studies on the reinforcing effect of boron nitride nanotubes and carbon nanotubes through experimental pull-out test and in-silico simulation are summarized. In addition, the conflicting aspect of the two different nanotubes with structural defects in their side wall is discussed on the viscoelastic damping performance of nanocomposites.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5D
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• pp.831-838
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• 2006

An experimental/analytic study has been conducted to understand the adverse effects of low vehicle speed, high axle load and high tire pressure on the performance of asphalt pavements. Of 33 asphalt sections at KHC test road, two sections having different base layer thickness (180 mm versus 280 mm) are adopted for rollover tests. During the test, a standard three-axle dump truck maintains a steady state condition as moving along the wheel path of a passing lane, and lateral offsets and real travel speed are measured with a laser-based wandering system. Test results suggest that vehicle speed affects both longitudinal and transverse strains at the bottom of asphalt layer (290 mm and 390 mm below the surface), and even slightly influences the measured vertical stresses at the top of subbase and subgrade due to the dynamic effect of rolling vehicle. Since the anisotropic nature of asphalt-aggregate mixtures, the difference between longitudinal and transverse strains appears prominent throughout the measurements. As the thickness of asphalt pavement increases, the measured lateral strains become larger than its corresponding longitudinal strains. Over the limited testing conditions, it is concluded that higher axle weight and higher tire pressures induce more strains and vertical stresses, leading to a premature deterioration of pavements. Finally, a layered elastic analysis overestimates the maximum strains measured under the 1st axle load, while underestimating the maximum vertical stress in both pavement sections.

• International Journal of Highway Engineering
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• v.8 no.3 s.29
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• pp.129-141
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• 2006

The vertical soil pressure developed in the granular layer of asphalt pavement system is influenced by various factors, including the wheel load magnitude, the loading speed, and asphalt pavement temperature. This research observed the distribution of vertical soil pressure in pavement supporting layer by investigating measured data from soil pressure gage in the KHC Test Road. The existing specification of subbase and subgrade compaction was also evaluated with measured vertical pressure. The finite element analysis was conducted to verify the accuracy of results with measured data because it can maximize research capacity without significant field test. The test data was collected from A5, A7, A14, and A15 test sections at August, September, and November 2004 and August 2005. Those test sections and test data were selected because they had best quality. The size of influence area was evaluated and the vertical pressure variation was investigated with respect to load level, load speed, and pavement temperature. The lower speed, higher load level, and higher pavement temperature increased the vertical pressure and reduced the area of influence. The finite element result showed the similar trend of vertical pressure variation in comparison with measured data. The specification of compaction quality for subbase and subgrade is higher than the level of vertical pressure measured with truck load so that it should be lurker investigated.