• 약학회지
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• 제25권4호
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• pp.175-179
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• 1981

Rheological studies on the gelatin hydrogels were carried out by rheometer. In the temperature range of $32^{\circ}~90{\circ}C$, the viscosities of the gelatin hydrogels were measured. In order to observe the formation of gel structure, the stress-relaxation tests of the creep-curves were investigated. The structure of viscoelastic substance could be considered of a three dimensional crosslinked matrix. As the result viscoelastic coefficients were obtained by Maxwell element, which are correspond to the network structure. From the relationship between the stress-relaxation time and temperature, activation energy correspond to breaking the formation of gels was calculated to be 13.91kcal/mole.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.546-552
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• 2000

Dynamic behavior of laminated composite plates undergoing moderately large deflection is investigated taking into account the viscoelastic behavior of material properties. Based on von Karman's non-linear deformation theory and Boltzmann's superposition principle, non-linear and hereditary type governing equations are derived. Finite element analysis and the method of multiple scales is applied to examine the effect of large amplitude on the dissipative nature of viscoelastic laminated plates.

• Korea-Australia Rheology Journal
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• 제20권4호
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• pp.221-226
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• 2008

The purpose of this study was to compare rheological properties of six dental interocclusal recording materials and to investigate the effect of temperature on the rheological properties during setting. Five polyvinylsiloxane materials and one polyether material were investigated in this study. The storage modulus (G') and the loss factor ($tan{\delta}$) were measured from 30s after mixing during setting, using the universal dynamic spectrometer. Viscoelastic properties were evaluated by means of G' and $tan{\delta}$ from 5 repeats at $21^{\circ}C$ and $33^{\circ}C$. Individual changes during setting were also evaluated. All data were statistically analyzed using one-way ANOVA and multiple comparison $Scheff{\acute{e}}$ test at the significance level of 0.05. The mean of G was checked at $t_{set}$ (the setting time provided from manufacturer) and $t_{300}$ (the end of experimental time) and the mean of $tan{\delta}$ was checked at to and $t_{set}$. Whereas the increase of the G' value showed generally exponential changes at $21^{\circ}C$, the change of the G' value at $33^{\circ}C$ displayed sigmoidal curves during setting. The change of loss factor $tan{\delta}$ during setting varied. Within the limitations of this study, dental interocclusal recording materials had different viscoelastic properties and most of the materials showed different fluidity at $21^{\circ}C$ and $33^{\circ}C$.

• 한국식품과학회지
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• 제29권5호
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• pp.932-938
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• 1997

Changes in viscosity and dynamic theological properties of Job's-tears were measured by Bohlin dynamic tester as a function of moisture, and measurement was performed within a linear viscoelastic range. The result of the shear stress vs shear rate of Job's-tears at different moisture contents $(50{\sim}75%)$ was applied to mathematical models and Herschel-Bulkley model showed the highest correlation coefficient. Lower moisture content (55%) produced higher yield stress and consistency index, but lower flow behavior index, whereas higher moisture content showed reverse effects. Job's-tears with $50{\sim}70%$ moisture contents showed a higher storage modulus (G') than loss modulus (G') at all frequencies, showing a higher concentrated polymer characteristics. However, higher moisture content (>75%) showed crossover point between G' and G', and frequency dependency. As the moisture content was increased, the amount of viscoelastic properties such as G', G', complex viscosity decreased during heating, and initial temperature and miximum value of viscoelastic properties shifted to higher temperatures, representing the moisture-dependence of Job's-tears upon theological properties.

• Elastomers and Composites
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• 제55권3호
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• pp.215-221
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• 2020

Silica/SBR (styrene-butadiene rubber) compounds are the primary constituents of tire treads. Furthermore, the excellent dynamic viscoelastic properties of silica lead to good fuel efficiencies. However, the silanol group on the surface of silica does not mix well with non-polar rubber because of its polarity. This incompatibility causes aggregation due to the occurrence of hydrogen bonding between the hydroxyl groups, thereby reducing the dispersibility of silica. Recently, the wet master batch (WMB) process has been applied to overcome these disadvantages, and research on silica dispersants that can be used in the WMB process has been increasing. In this study, we prepared silica/SBR compounds by using three types of eco-friendly cellulose-based dispersants in the WMB process, namely: cellulose-, sodium carboxymethyl cellulose, and nanocellulose-based dispersants. Subsequently, we compared the vulcanization characteristics, viscoelastic properties, and mechanical properties of the compounds. The silica dispersibility in the rubber compounds was improved with the addition of the nano-cellulose dispersant, resulting in the enhancement of the workability, hardness, tensile strength, and wear resistance of the SBR compound.

• Journal of Pharmaceutical Investigation
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• 제39권3호
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• pp.185-199
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• 2009

Using a strain-controlled rheometer [Advanced Rheometric Expansion System (ARES)], the steady shear flow properties and the dynamic viscoelastic properties of $Antiphlamine-S^{(R)}$ lotion have been measured at $20^{\circ}C$ (storage temperature) and $37^{\circ}C$ (body temperature). In this article, the temperature dependence of the linear viscoelastic behavior was firstly reported from the experimental data obtained from a temperature-sweep test. The steady shear flow behavior was secondly reported and then the effect of shear rate on this behavior was discussed in detail. In addition, several inelastic-viscoplastic flow models including a yield stress parameter were employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models was examined by calculating the various material parameters. The angular frequency dependence of the linear viscoelastic behavior was nextly explained and quantitatively predicted using a fractional derivative model. Finally, the strain amplitude dependence of the dynamic viscoelastic behavior was discussed in full to elucidate a nonlinear rheological behavior in large amplitude oscillatory shear flow fields. Main findings obtained from this study can be summarized as follows : (1) The linear viscoelastic behavior is almostly independent of temperature over a temperature range of $15{\sim}40^{circ}C$. (2) The steady shear viscosity is sharply decreased as an increase in shear rate, demonstrating a pronounced Non-Newtonian shear-thinning flow behavior. (3) The shear stress tends to approach a limiting constant value as a decrease in shear rate, exhibiting an existence of a yield stress. (4) The Herschel-Bulkley, Mizrahi-Berk and Heinz-Casson models are all applicable and have an equivalent validity to quantitatively describe the steady shear flow behavior of $Antiphlamine-S^{(R)}$ lotion whereas both the Bingham and Casson models do not give a good applicability. (5) In small amplitude oscillatory shear flow fields, the storage modulus is always greater than the loss modulus over an entire range of angular frequencies tested and both moduli show a slight dependence on angular frequency. This means that the linear viscoelastic behavior of $Antiphlamine-S^{(R)}$ lotion is dominated by an elastic nature rather than a viscous feature and that a gel-like structure is present in this system. (6) In large amplitude oscillatory shear flow fields, the storage modulus shows a nonlinear strain-thinning behavior at strain amplitude range larger than 10 % while the loss modulus exhibits a weak strain-overshoot behavior up to a strain amplitude of 50 % beyond which followed by a decrease in loss modulus with an increase in strain amplitude. (7) At sufficiently large strain amplitude range (${\gamma}_0$>100 %), the loss modulus is found to be greater than the storage modulus, indicating that a viscous property becomes superior to an elastic character in large shear deformations.

• Korean Journal of Radiology
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• 제24권6호
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• pp.564-573
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• 2023

Objective: To investigate the feasibility of assessing the viscoelastic properties of the brain using magnetic resonance elastography (MRE) and a novel MRE transducer to determine the relationship between the viscoelastic properties and glymphatic function in neurologically normal individuals. Materials and Methods: This prospective study included 47 neurologically normal individuals aged 23-74 years (male-to-female ratio, 21:26). The MRE was acquired using a gravitational transducer based on a rotational eccentric mass as the driving system. The magnitude of the complex shear modulus |G^*| and the phase angle 𝛗 were measured in the centrum semiovale area. To evaluate glymphatic function, the Diffusion Tensor Image Analysis Along the Perivascular Space (DTI-ALPS) method was utilized and the ALPS index was calculated. Univariable and multivariable (variables with P < 0.2 from the univariable analysis) linear regression analyses were performed for |G^*| and 𝛗 and included sex, age, normalized white matter hyperintensity (WMH) volume, brain parenchymal volume, and ALPS index as covariates. Results: In the univariable analysis for |G^*|, age (P = 0.005), brain parenchymal volume (P = 0.152), normalized WMH volume (P = 0.011), and ALPS index (P = 0.005) were identified as candidates with P < 0.2. In the multivariable analysis, only the ALPS index was independently associated with |G^*|, showing a positive relationship (β = 0.300, P = 0.029). For 𝛗, normalized WMH volume (P = 0.128) and ALPS index (P = 0.015) were identified as candidates for multivariable analysis, and only the ALPS index was independently associated with 𝛗 (β = 0.057, P = 0.039). Conclusion: Brain MRE using a gravitational transducer is feasible in neurologically normal individuals over a wide age range. The significant correlation between the viscoelastic properties of the brain and glymphatic function suggests that a more organized or preserved microenvironment of the brain parenchyma is associated with a more unimpeded glymphatic fluid flow.

• 대한관절경학회지
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• 제1권1호
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• pp.9-19
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• 1997

Biomechanics of the soft tissue arc different from that of bone. Soft tissue has characteristics of nonhomogeneous, no-linear, anisotropic, viscoelastic, and finite deformation. Biomechanics of ACL, one of the soft tissue, are briefly described : structural and mechanical properties, viscoelastic response, immobilization, kinematics and static function.

• 마이크로전자및패키징학회지
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• 제29권3호
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• pp.43-48
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• 2022

본 연구에서는 재료의 이방성 점탄성 거동을 고려한 해석 기법을 개발하여 휨(Warpage) 해석의 정합성을 개선하고자 하였다. 먼저, 이방성 점탄성 거동 구현을 위해 구리 패턴(Cu trace) 및 범프(Bump)가 존재하는 패키지를 모델링 하였다. 복잡한 형상의 범프 영역은 대표체적요소 모델을 기반으로 등가 이방성 점탄성 물성 및 열 팽창계수를 도출하였다. 도출된 물성을 기반으로 패키지에 0~125도의 열 주기(Thermal cycle)를 가하였으며, 열 주기에 따른 패키지의 휨 경향을 확인하였다. 해석 결과의 검증을 위해 해석 모델과 동일한 패키지를 제작하였고, 쉐도우 모아레 간섭계(Shadow Moire interferometer)를 통해 열 주기에 따른 실제 패키지의 휨 정도를 측정하였다. 결과적으로 구리 패턴, 범프 등의 요소가 고려된 등가 이방성 점탄성 해석 기법의 적용으로 5 ㎛ 이내의 오차로 패키지의 휨 정도를 계산하고 휨의 형태를 예측할 수 있었다.

• 마이크로전자및패키징학회지
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• 제19권2호
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• pp.17-28
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• 2012

WB-PBGA 패키지를 구성하는 솔더볼 재료나 수지 복합재의 열-기계적 물성치는 온도에 대단히 큰 영향을 받을 뿐 아니라, 온도가 유지되는 시간에도 큰 영향을 받는 것으로 알려져 있다. 본 논문에서는 무연 솔더 WB-PBGA 패키지의 변형 거동을 신뢰성 있게 해석하기 위하여 재료의 비선형성을 고려한 유한요소 해석을 수행하고 무아레 간섭계 실험결과와 비교하였다. 먼저 수지 복합재의 점탄성 거동을 파악하기 위해 수지 접합재와 패키지 기판으로 구성된 이종접합체를 대상으로 하여 수지 복합재의 온도와 시간에 종속적인 점탄성 거동에 대해 유한요소 해석을 수행하고 결과를 분석하였다. 무연 솔더가 실장된 WB-PBGA의 열-기계적 거동을 파악하기 위하여 솔더는 점소성 물성치를, 수지 복합재는 점탄성 물성치를 적용하여 온도 변화에 따르는 유한요소 변형해석을 수행하여 실험결과와 비교하였다. 결과적으로 패키지의 변형은 수지 복합재의 재료 모델에 따라 대단히 크게 달라지며, 수지 복합재는 온도와 시간에 영향을 받는 점탄성 물성으로 해석해야 함을 알 수 있었다. 본 논문에서와 같은 SAC 계열 무연 솔더 WB-PBGA 패키지의 경우 유리전이 온도가 $135^{\circ}C$ 정도로 비교적 높은 B-type 수지 복합재의 점탄성 물성치를 적용했을 때 상대적으로 신뢰성 있는 해석 결과를 얻을 수 있는 것으로 밝혀졌다.