• 폴리머
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• 제33권6호
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• pp.581-587
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• 2009

PLA와 PEG를 사용하여 용융블렌드 방법으로 PLA/PEG 블렌드 섬유를 제조한 후 in vitro 환경조건인 pH7.4, 온도 $37\;^{\circ}C$의 완충용액에서 1~8주 동안 가수분해한 다음 무게감량률 및 인장강도 등에 미치는 영향을 검토하였다. 가수분해 시간이 1주에서 8주까지 증가함에 따라 블렌드 시간은 10~30분으로, PEG 함량은 5~30 wt%로 증가할수록 PLA/PEG 블렌드 섬유의 무게감량률은 증가하는 경향이, 인장강도 및 인장탄성률은 감소하는 경향이 현저하게 나타남을 확인하였다. 결론적으로 가수분해 시간 2주까지는 PLA/PEG 블렌드 섬유의 무게 감량률은 약 0.9% 이내이고 강도유지율은 약 90% 이상을 나타냄으로써 임계상처치유기간 중 양호한 강도가 유지될 수 있음을 확인하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제33권7호
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• pp.1180-1190
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• 2020

Objective: To develop healthier comminuted meat products to meet consumer demand, the gel properties, rheological properties, microstructure and water distribution of pork meat batters formulated with various amounts of bamboo shoot dietary fiber (BSDF) were investigated. Methods: Different levels of BSDF (0% to 4%) were added to pork batters, and the pH, color, water-holding capacity, texture and rheological properties of pork batters were determined. Then, pork batters were analyzed for their microstructure and water distribution using scanning electron microscopy (SEM) and low-field nuclear magnetic resonance (LF-NMR). Results: Compared with the control, BSDF addition into meat batters showed a significant reduction in L^*-value and a significant increase in b^*-value (p<0.05). BSDF addition of up to 4% reduced the pH value of pork batters by approximately 0.15 units; however, the cooking loss and expressible water loss decreased significantly (p<0.05) with the increased addition of BSDF. The hardness and gel strength were noticeably enhanced (p<0.05) as the content of BSDF increased. The rheological results showed that BSDF added into pork batters produced higher storage modulus (G') and loss modulus (G") values. The SEM images suggested that the addition of BSDF could promote pork batters to form a more uniform and compact microstructure. The proportion of immobilized water increased significantly (p<0.05), while the population of free water was decreased (p<0.05), indicating that BSDF improved the water-holding capability of pork batters by decreasing the fraction of free water. Conclusion: BSDF could improve the gel properties, rheological properties and water distribution of pork meat batters and decrease the proportion of free water, suggesting that BSDF has great potential as an effective binder in comminuted meat products.

• Journal of Pharmaceutical Investigation
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• 제29권4호
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• pp.295-307
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• 1999

Using a Rheometries Fluids Spectrometer (RFS II), the dynamic viscoelastic properties of aqueous poly(ethylene oxide) (PEO) solutions in small amplitude oscillatory shear flow fields have been measured over a wide range of angular frequencies. The angular frequency dependence of the storage and loss moduli at various molecular weights and concentrations was reported in detail, and the result was interpreted using the concept of a Deborah number De. In addition, the experimentally determined critical angular frequency at which the storage and loss moduli become equivalent was compared with the calculated characteristic time (or its inverse value), and their physical significance in analyzing the dynamic viscoelastic behavior was discussed. Finally, the relationship between steady shear flow and dynamic viscoelstic properties was examined by evaluating the applicability of some proposed models that describe the correlations between steady flow viscosity and dynamic viscosity, dynamic fluidity, and complex viscosity. Main results obtained from this study can be summarized as follows: (1) At lower angular frequencies where De<1, the loss modulus is larger than the storage modulus. However, such a relation between the two moduli is reversed at higher angular frequencies where De>l, indicating that the elastic behavior becomes dominant to the viscous behavior at frequency range higher than a critical angular frequency. (2) A critical angular frequency is decreased as an increase in concentration and/or molecular weight. Both the viscous and elastic properties show a stronger dependence on the molecular weight than on the concentration. (3) A characteristic time is increased with increasing concentration and/or molecular weight. The power-law relationship holds between the inverse value of a characteristic time and a critical angular frequency. (4) Among the previously proposed models, the Cox-Merz rule implying the equivalence between the steady flow viscosity and the magnitude of the complex viscosity has the best validity. The Osaki relation can be regarded to some extent as a suitable model. However, the DeWitt, Pao and HusebyBlyler models are not applicable to describe the correlations between steady shear flow and dynamic viscoelastic properties.

• Composites Research
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• 제13권3호
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• pp.30-37
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• 2000

계면상 조건과 단섬유 함유량 증가에 따른 강화고무의 동적 특성에 대해 실험적 고찰을 하였다. 손실계수는 대체적으로 섬유 함유량 증가에 따라 감소하였고 계면상 조건에 따라 다른 경향을 보였다. 계면 조건이 우수할수록 손실탄성율, $E_2$ 는 낮게 나타났다. 또한 동배율은 섬유 함유량 증가에 따라 감소하였고, 계면상 조건이 우수할수록 크게 감소하였다. 따라서 단섬유 강화고무는 진동수비가 $\sqrt{2}$이상에서 더 큰 진동절연 효과가 있다고 할 수 있다. 손실계수와 동배률의 관계로부터, 자동차의 엔진과 차체의 진동을 절연하는 부품인 Engine Mount Rubber의 적용가능성을 검토하였다.

• 한국정밀공학회지
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• 제20권1호
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• pp.172-178
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• 2003

Two types of bolted lap joints, one with a viscoelastic layer and the other without the viscoelastic layer were chosen to analyze the dynamic characteristics of the joints with the mechanical properties of the bolts in the joints are considered as computational variables. The finite element method was used along with the modal testing to verify the PEM model. The results in the bolted lap joints reveal that the higher the Young's modulus for the bolts we use the higher the natural frequencies we obtain fur the joints. However, the natural frequency differences in the first and second mode are not substantial but become noticeable in the higher modes. Lower natural frequencies were obtained for the bolted lap joints with the viscoelastic layer when compared with those of the bolted lap joints without the viscoelastic layer. And the differences in the natural frequencies for the two types of joints are relatively small in the first and second mode whereas in the higher mode the differences become significant. The loss factors were observed to be significant especially in the second mode for the bolted lap joints with the viscoelastic layer.

• Advances in aircraft and spacecraft science
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• 제2권1호
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• pp.57-76
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• 2015

We investigated complex damped modes in beams in the presence of a viscoelastic layer sandwiched between two elastic layers. The problem was solved using two approaches, (1) Rayleigh beam theory and analyzed using the Ritz method, and (2) by using 2D plane stress elasticity based finite-element method. The damping in the layers was modeled using the complex modulus. Simply-supported, cantilever, and viscously supported boundary conditions were considered in this study. Simple trigonometric functions were used as admissible functions in the Ritz method. The key idea behind sandwich structure is to increase damping in a beam as affected by the presence of a highly-damped core layer vibrating mainly in shear. Different assumptions are utilized in the literature, to model shear deformation in the core layer. In this manuscript, we used FEM without any kinematic assumptions for the transverse shear in both the core and elastic layers. Moreover, numerical examples were studied, where the base and constraining layers were also damped. The loss factor was calculated by modal strain energy method, and by solving a complex eigenvalue problem. The efficiency of the modal strain energy method was tested for different loss factors in the core layer. Complex mode shapes of the beam were also examined in the study, and a comparison was made between viscoelastically and viscously damped structures. The numerical results were compared with those available in the literature, and the results were found to be satisfactory.

• 한국소음진동공학회논문집
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• 제16권7호
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• pp.690-696
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• 2006

Thickness of damping layer in sandwich plate needs to be optimized in order to make modal loss factor of the sandwich plate maximum. Since previous studies were interested in noise reductions over high frequency range, the modal properties were derived based on simply supported boundaries. This conventional formula is approximately applicable to other boundary conditions over high frequency range only. The purpose of this study is to propose a method to determine optimum damping layer thickness of sandwich plate for maximum modal damping in low frequency range when the boundary condition is not a simple support. The conventional RKU equation based on simply supported boundary is modified to reflect other boundary conditions and the modified RKU equation is subsequently applied to determine the optimum damping layer thickness for arbitrary conditions. In order to reflect frequency-dependent characteristics of elastic modulus of the damping layer, an iteration method is proposed in determining the modal properties. Test results on sandwich plates for optimum damping layer thickness are compared with predictions by the proposed method and conventional method.

• 대한화학회지
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• 제38권7호
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• pp.480-484
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• 1994

자외선 경화코팅 필름-기질 계면에서의 견딤성에 대하여 조사하였다. 특히, UV 경화 우레탄 아크릴레이트계 배합물에서 모노머 및 올리고머의 코팅필름 주름현상에 미치는 영향은 조사하였다. 실험결과, 주름현상은 DMTA이 손실모듈러스 피크가 넓고 shouldr가 있을수록 덜 나타났다. 특히, 변성된 방향족 우레탄 아크릴레이트를 지방족계에 첨가하므로서 hard하면서도 flexible한 코팅필름을 얻을 수 있음을 알 수 있었다. 따라서 주름현상 방지효과는 높은 손실모듈러스값 때문인 것으로 나타났다. SEM 및 instron 실험결과도 위의 결론을 입증하고 있음을 알 수 있었다.

• Steel and Composite Structures
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• 제22권3호
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• pp.567-587
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• 2016

The present investigation is to study the plane wave propagation and reflection of plane waves in a homogeneous transversely isotropic magnetothermoelastic medium with two temperature and rotation in the context of GN Type-II and Type-III (1993) theory of thermoelasticity. It is found that, for two dimensional assumed model, there exist three types of coupled longitudinal waves, namely quasi-longitudinal wave (QL), quasi-transverse wave (QTS) and quasi-thermal waves (QT). The different characteristics of waves like phase velocity, attenuation coefficients, specific loss and penetration depth are computed numerically and depicted graphically. The phenomenon of reflection coefficients due to quasi-waves at a plane stress free with thermally insulated boundary is investigated. The ratios of the linear algebraic equations. These amplitude ratios are used further to calculate the shares of different scattered waves in the energy of incident wave. The modulus of the amplitude and energy ratios with the angle of incidence are computed for a particular numerical model. The conservation of energy at the free surface is verified. The effect of energy dissipation and two temperatures on the energy ratios are depicted graphically and discussed. Some special cases of interest are also discussed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.624-629
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• 2001

Two types of bolted lap joints, one with a viscoelastic layer and the other without the viscoelastic layer were chosen to analyze the dynamic characteristics of the joints with the mechanical properties of the bolts of the joints being taken as computational variables. The finite element method was used along with the impact hammer technique to verify the FEM model. The results in the bolted lap joints reveal that the higher the Young's Modulus for the bolts are the higher the natural frequencies results for the joints. However, the natural frequency differences in the first and second mode are not substantial but become noticeable in the higher modes. Lower natural frequencies were obtained for the bolted lap joints with the viscoelastic layer when compared with those of the bolted lap joints without the viscoelastic layer. And the differences in the natural frequencies for the two types of joints are relatively small in the first and second mode whereas in the higher mode the differences become significant. The loss factors were observed to be significant especially in the second mode for the bolted lap joints with the viscoelastic layer.