• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.2
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• pp.79-89
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• 1997

The objective of this paper is to investigate the mechanical characteristics of the laminated rubber bearings (LRBs) for the seismic isolation. The evaluations of the proposed equations of the LRB horizontal stiffness are carried out and these equations are extended to the visco-elastic problems to investigate the damping amplifications of LRBs. The stability evaluation of LRBs is also performed. For investigation of the dynamic characteristics of LRBs, the horizontal stiffness equations of the LRBs considering the P-delta effects are applied to the modeling of a seismically isolated structure and the earthquake response time history analyses are carried out. From this research, the proposed simple equation of the horizontal stiffness of LRB is so useful for the design loads and easily extended to the visco-elastic problems. Through the stability evaluation of LRB, the increasing ratio of the total rubber thickness of the LRB severely decrecises the bucking load than the increasing ratio of unit rubber thickness. From the comparison of the dynamic shear deflection of LRB, the analysis results are in good agreement with those of the experiments.

• International Journal of Highway Engineering
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• v.7 no.4 s.26
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• pp.203-210
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• 2005

The penetration and viscosity tests have been used for the evaluation of the aged asphalt binder performance change. The improved test method has been required because the conventional tests could not evaluate the viscoelastic characteristics and the real behaviour of the aged asphalt binder. The conventional test methods using a different short term aged asphalt binder were tested and the test results were expressed as the penetration index and the residual penetration. The oscillatory and rotational mode tests were performed to find out the rheological characteristics of the short term aged asphalt binder in this study. The test results showed that the change of testing frequency, the speed of the vehicle effects the complex modules and phase angles. The creep compliance and shear viscosity also showed the different test results when the short term aged asphalt binders were tested. The rheological behavior should consider when the pavement design is conducted.

• Journal of the Korean Chemical Society
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• v.50 no.3
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• pp.196-202
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• 2006

The self diffusion distributions of viscoelastic molten polyurethanes were determined from the relationship between the relaxation spectra and the distribution of self diffusion. The relaxation spectra of ester, PCL and PCL dyed type molten polyurethanes were obtained by applying the experimental stress relaxation curves to the theoretical equation of the Ree-Eyring and Maxwell non-Newtonian model(REM model) from computer calculation. The experiments were carried out at various temperatures using the physica rheometer with the temperature controller. The self diffusion and hole distance of amorphous region of polyurethane samples were investigated by experiments of stress relaxation. The diffusion coefficients and hole volumes were calculated from rheological parameters and crystallite size in order to study the diffusion of flow segments in amorphous region. It was observed that the relaxation spectra and self diffusions of these polymer samples are directly related to the distribution of molecular weights, viscosities, hole volumes and activation energies of flow segments.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.12
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• pp.24-29
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• 2021

Recently, owing to the high demand for eco-friendly cars in the automotive industry, noise and vibrations have become major challenges. The use of laminated damping steel is increasing in response to these demands. Laminated damping steel is primarily used in sound insulation plates. The vibration energy is converted into thermal energy due to the viscoelastic resin being located between two steel sheets and being able to damp the vibrations when an external force, such as, noise or vibration is applied to the steel plate. Laminated damping steel is chiefly applied to dash panels in automotive body parts, and because of its structure, junction technology for bonding with other components is necessary. However, there has not been sufficient research conducted on junctions. In this study, regardless of the electrode shape, in the range of 4.0 ~ 8.0 kA welding current, the same welding force and welding time were applied which were 2.8 kN and 200 m/s (12 cycles) and the tensile shear load and nugget size were analyzed after the resistance spot welding between different materials of laminated damping steel with a thickness of 1.035 mm. The results show that in the range of 5 ~ 8 kA welding current, 1.035 mm laminated damping steel meets the MS181-15 standard, which is the technical standard of Hyundai-Kia Motors.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.5
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• pp.399-405
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• 2010

The accumulated displacements and fatigues of rock are increased by the stress-hysteresis, induced from repeated frost-thawing. Also the shear strength is decreased by them continuously. The stress-hysteresis is affected by the atmospheric temperature changes, whose behavior is visco-elasticity, usually. Therefore, to do ideal body analysis, Kelvin model could be used to analyze the frost-thawing behavior in winter. In general, rock slope failure occurs by the deterioration of rocks, which is caused by the repetition of freezing-thawing process. In order to keep the safety of such rock mass structures the deterioration process of rock needs to be described quantitatively using some meaningful parameters. In this work, the deterioration process in freezing-thawing cycle of tuff, which is a famous soft porous rock, is investigated through laboratory tests and successfully described as a differential equation for the change of porosity. And then, the deterioration of the mechanical properties of rock, such as Young's modulus and uniaxial compressive strength, are quantitatively described as a function of the porosity.

• Korean Journal of Materials Research
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• v.7 no.4
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• pp.339-346
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• 1997

회전 불밀에 있어서 볼의 운동을 비선형 spring과 비선형 deshpot로 구성된 Kelvin모델을 사용한 DEM(Distinct Element Method;개별요소법)에 의하여 2차원으로 해석하였다. 모델에 있어서 점성계수는 볼과 밀벽사이의 반발실험 데이타로 부터 결정하였다. 각볼의 동적인 운동은 비선형 점탄성과 Newton의 운동법칙를 기초로하여 모사되었다. 밀이 회전하는 동안 볼의 궤적과 동적인 운동은 실제 실험에 의한 밀내에서의 볼의 운동고 잘 일치하였다. 본 연구에서 제안된 모델 시뮬레이션은 회전 볼밀내의 실제의 3차원인 볼의 운동에 대한 해석에 중요한 단서가 될 수 있었다. 볼의 운동고 운동에너지는 회전 볼밀의 속도와 볼의 충진율에 의해 크게 영향을 받았다.

• Journal of KSNVE
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• v.10 no.3
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• pp.531-535
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• 2000

A three-parameter model of viscoelastic damper which has a non-linear spring as an element is incorporated into an oscillator. The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by get analytic solutions of the system. The frequency-response curves show that multiple solutions co-exist and that the jump phenomena can occur. In addition it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurences of such non-linear phenomena. A direct time intergration of the original equation of motion validifies the use of the harmonic balance method to this sort of problem.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.543-546
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• 2000

Static and dynamic experiments were done to study on the restitution behaviors of strings. The elastic and viscoelastic model were compared. To apply a linear viscoelastic model (Kelvin model) to longitudinal behaviors of strings, static and dynamic tensile tests were done. Using their results, it should be intended to acquire damped stress (Stress related to velocity), and to calculate the viscoelastic coefficient. Fixing both ends, string was pushed by the loadcell attached to the tensile tester. The experimental results were in accordance with the calculated results using the Kelvin model acquired from the results of longitudinal tensile test. But the results of falling mass experiments, the behaviors of strings were near to elastic model. The clamping condition of strings in both sides has an effected on the value of COR. The smaller contact area, the grower the value of COR.

• Journal of KSNVE
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• v.9 no.1
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• pp.174-183
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• 1999

An analytical model for the lateral vibration of beams with a bonded lap joint and partial layered dampers has been proposed in this paper. Both shear and normal forces acting along the interface between the elastic and viscoelastic layers were considered in the vibration analysis. Analytical results were compared with those obtained by a finite element method. Effects of the size and location of layers in partial dampers on system loss factor($\eta_s$) and resonant frequency($\omega_r$) were studied. which showed that partial dampers adhered to the site exhibiting the maximum amplitude of vibration were most influential in the increase of $\eta_s$ and the decrease of $\omega_r$. Specific system loss factor( $\eta_s$ divided by total mass of system) was also evaluated in the analysis.

• Korean Journal of Food Science and Technology
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• v.31 no.3
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• pp.870-874
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• 1999

농후한 점도영역에서 감귤류 펙틴용액에 NaCl을 첨가하였을 때 점도 및 점탄성 변화를 연구하였다. NaCl의 농도가 증가함에 따라 펙틴용액의 점도도 점차 증가하였으며, 1.5 M의 NaCl을 첨가한 경우 점도가 약 3배 증가하였다. NaCl의 첨가에 따른 점도특성의 일반화 곡선으로서 ${\eta}/{\eta}_0$ 대 $\dot{\gamma}/\dot{\gamma}_{0.8}$ 관계는 상대적으로 낮은 중첩도를 보였다. Zero-shear viscosity $({\eta}_0)$와 NaCl 농도(C)와는 ${\eta}_0\;{\propto}\;10^{0.32C}$의 관계를 보였으며, 이때 상관계수(R2)는 0.995였다. 한편, NaCl 농도가 증가함에 따라 저장탄성률(G#)과 손실탄성률(G@)이 모두 증가하였다.