• Structural Monitoring and Maintenance
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• 제3권2호
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• pp.175-194
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• 2016

Based on the change of traditional viscoelastic damper structure, a brand-new damper is designed to control simultaneously the translational vibration and the rotational vibration for platforms. Experimental study has been carried out on the mechanical properties of viscoelastic material and on its multi-dimensional seismic response control effect of viscoelastic damper. Three types of viscoelastic dampers with different shapes of viscoelastic material are designed to test the influence of excited frequency, strain amplitude and ambient temperature on the mechanical property parameters such as circular dissipation per unit, equivalent stiffness, loss factor and storage shear modulus. Then, shaking table tests are done on a group of single-storey platform systems containing one symmetric platform and three asymmetric platforms with different eccentric forms. Experimental results show that the simulation precision of the restoring force model is rather good for the shear deformation of viscoelastic damper and is also satisfied for the torsion deformation and combined deformations of viscoelastic damper. The shaking table tests have verified that the new-type viscoelastic damper is capable of mitigating the multi-dimensional seismic response of offshore platform.

• Korea-Australia Rheology Journal
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• 제20권1호
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• pp.27-34
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• 2008

Clay suspensions in liquid polymers exhibit a time-dependent behaviour that includes viscoelastic as well as thixotropic features. Because of the presence of interacting clay platelets, particulate networks can develop, which are broken down during flow and rebuild upon cessation of the flow. Here, the use of thixotropic techniques in probing flow-induced structures in nanocomposites is explored with data on a hectorite-poly(isobutylene) model system. By means of fast stress jump measurements the hydrodynamic contributions to the steady state stresses are determined as well as those caused by the stretching of the clay floes. Flow reversal measurements do not provide a clear indication of flow-induced anisotropy in the present case. The recovery of the clay microstructure upon cessation of flow is followed by means of overshoot and dynamic measurements. The development of a particulate network is detected by the appearance and growth of a low frequency plateau of the storage moduli. The modulus-frequency curves after various rest times collapse onto universal master curves, regardless of the pre-shear history or temperature. The scaling factors for this master curve are the crossover parameters. The crossover moduli are nearly a linear function of the crossover frequency, the relation being identical for recovery after shearing at different shear rates. This function depends, however, on temperature.

• Korea-Australia Rheology Journal
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• 제16권3호
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• pp.153-160
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• 2004

Open microcellular foams having small-sized cell and good mechanical properties are desirable for many practical applications. As an effort to reduce the cell size, the microcellular foams combining viscosity improvers into the conventional formulation of styrene and water system were prepared via high internal phase emulsion polymerization. Since the material properties of foam are closely related to the solution properties of emulsion state before polymerization, the flow behavior of emulsions was investigated using a controlled stress rheometer. The yield stress and the storage modulus increased as viscosity improver concentration and agitation speed increased, due to the reduced cell size reflecting both a competition between the continuous phase viscosity and the viscosity ratio and an increase of shear force. Appreciable tendency was found between the rheological data of emulsions and the cell sizes of polymerized foams. Cell size reduction with the concentration of viscosity improver could be explained by the relation between capillary number and viscosity ratio. A correlative study for the cell size reduction with agitation speed was also attempted and the result was in a good accordance with the hydrodynamic theory.

• Food Science and Biotechnology
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• 제15권6호
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• pp.856-859
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• 2006

The effects of moisture content on non-fracture dynamic properties and fracture gel quality of Pacific whiting surimi were investigated to determine their relationships. Surimi samples were tested at various moisture contents (75, 78, and 81 %). Torsion test showed that shear stress decreased rapidly and strain values decreased gradually as moisture concentration increased. Dynamic storage modulus (G') also decreased as moisture content increased. A strong positive correlation ($R^2=0.90$ to 0.99) was found between the G' measured at temperatures between 10 and $45^{\circ}C$ and fracture stress values. The results indicate that dynamic rheological measurements could be used as a tool for early gel quality assessment.

• 구강회복응용과학지
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• 제24권3호
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• pp.311-316
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• 2008

Calcium phosphate cement (CPC)는 우수한 생체 친화성을 바탕으로 치과 및 의과 쪽에서 성공적인 bone substitute로 사용되어 왔다. 긴 경화시간 및 washout tendency 등 CPC의 단점을 개선하기 위해 다양한 종류의 경화액 및 첨가제등에 대한 연구가 이루어졌다. 그러나 첨가제의 종류에 따른 CPC paste의 점탄성을 정량적으로 비교한 연구는 많지 않다. 이 연구에서는 2% hydroxyprophyl methylcellulose (HPMC)와 35% polyacrylic acid (PAA)의 두 가지 경화액과 혼합된 CPC의 유변학적 성질을 관찰하고 비교하고자 하였다. Dicalcium phosphate dihydrate (DCPD)를 2% HPMC 및 35% PAA와 각각 1:1의 분액비로 30초간 섞은 후 cone and plate geometry를 가지는 rheometer를 사용하여 frequency sweep test와 time sweep test를 통해 shear storage modulus (G'), shear loss modulus (G''), 그리고 complex viscosity (${\eta}^*$)를 측정하였다. 2% HPMC군과 35% PAA군의 complex viscostiy의 차이를 Mann-whitney test with Bonferroni's collection을 사용하여 분석하였다. 실험결과 2% HPMC 및 35% PAA 군 모두에서 shear thinning과 yield behavior등 pseudoplastic property를 보였으며 complex viscosity는 HPMC 군에서 PAA 군보다 통계적으로 유의성 있게 높았다. (p<0.05).

• 한국도로학회논문집
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• 제20권1호
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• pp.47-58
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• 2018

PURPOSES : The purpose of this study is to evaluate the mechanical properties of a cold-recycling asphalt mixture used as a base layer and to determine the optimum emulsified-asphalt content for ensuring the mixture's performance. METHODS : The physical properties (storage stability, mixability, and workability) of three types of asphalt emulsion (CMS-1h, CSS-1h, and CSS-1hp) were evaluated using the rotational viscosity test. Asphalt emulsion residues, prepared according to the ASTM D 7497-09 standard, were evaluated for their rheological properties, including the $G*/sin{\delta}$and the dynamic shear modulus (${\mid}G*{\mid}$). In addition, the Marshall stability, indirect tensile strength, and tensile-strength ratio (TSR) were evaluated for the cold-recycling asphalt mixtures fabricated according to the type and contents of the emulsified asphalt. RESULTS : The CSS-1hp was found to be superior to the other two types in terms of storage stability, mixability, and workability, and its $G*/sin{\delta}$ value at high temperatures was higher than that of the other two types. From the dynamic shear modulus test, the CSS-1hp was also found to be superior to the other two types, with respect to low-temperature cracking and rutting resistance. The mixture test indicated that the indirect tensile strength and TSR increased with the increasing emulsified-asphalt content. However, the mixtures with one-percent emulsified-asphalt content did not meet the national specification in terms of the aggregate coverage (over 50%) and the indirect tensile strength (more than 0.4 MPa). CONCLUSIONS : The emulsified-asphalt performance varied greatly, depending on the type of base material and modifying additives; therefore, it is considered that this will have a great effect on the performance of the cold-recycling asphalt pavement. As the emulsified-asphalt content increased, the strength change was significant. Therefore, it is desirable to apply the strength properties as a factor for determining the optimum emulsified-asphalt content in the mix design. The 1% emulsified-asphalt content did not satisfy the strength and aggregate coverage criteria suggested by national standards. Therefore, the minimum emulsified-asphalt content should be specified to secure the performance.

• 한국철도학회논문집
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• 제11권4호
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• pp.357-363
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• 2008

본 연구에서는 염수분무환경에 노출된 철도차량 차체용 탄소섬유/에폭시 복합재의 내구성을 조사하였다. 염수환경시험을 위해서는 해수와 가장 유사하도록 5% 염화나트륨 염수용액을 제조하여 사용하였다. 본 연구에 적용된 시편은 T700 탄소섬유직물을 에폭시 수지에 함침시킨 형태의 복합재 평판에서 채취하였다. 기계적 특성 시험을 통해 인장특성, 굽힘특성, 전단특성을 평가하였으며 동역학 측정장치를 통해 저장탄성계수, 손실탄성계수, 그리고 tan $\delta$ 등의 열분석 특성을 평가하였다. 또한 적외선 분광분석을 통해 노출기간에 따른 화학구조 변화도 조사하였다. 연구결과에 따르면 강화섬유가 지배적인 역할을 하는 기계적 특성은 염수환경에 영향을 받지 않지만 수지가 지배적인 역할을 하는 기계적 특성은 노출기간이 길어짐에 따라 점차 감소하는 양상을 나타낸다. 저장탄성계수는 노출기간에 큰 영향을 받지는 않지만 유리전이온도는 염수환경에 영향을 받으며 노출기간이 길어지면 감소하는 양상을 나타낸다. FT/IR 선도에서 관찰된 피크의 세기는 노출기간에 다소 영향을 받지만 피크의 형상과 위치는 노출 기간에 따른 변화가 관찰되지 않는다. 이로 미루어 볼 때 본 연구에 적용된 탄소섬유/에폭시 복합재는 염수환경에 비교적 안정함을 알 수 있다.

• 한국식품과학회지
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• 제27권5호
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• pp.799-806
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• 1995

고유점도가 3.75 dL/g인 감귤류 펙틴 용액의 전단점도 및 점탄성에 대한 농도의존성을 연구하였다. 전형적인 자수법칙 흐름 현상이 2.0% 이상의 펙틴 농도에서 관찰되었으며, 전단점도의 전단속도 의존성은 농도의 증가에 따라 더욱 뚜렷하게 나타났다. ${\eta}_{sp.o}$ 대 $C[\eta]$를 양대수 좌표에 그렸을 때 묽은 영역에서 진한 영역으로의 전이를 나타내는 $C^{*}[\eta]$는 약 4.0이었으며, 이때 ${\eta}_{sp.o}$의 값은 약 10.0을 나타내었다. 묽은 용액$(C[\eta]과 진한 용액$(C[\eta]>C^{*}[\eta])$에서 ${\eta}_{sp.o}$ $C[\eta]$의 기울기는 각각 1.1과 4.5였다. 전단점도를 ${\eta}/{\eta_0}$ 대 ${\gamma}/{\gamma}_{0.8}$에 대하여 그렸을 때 $2{\sim}5%$의 농도에서는 잘 중첩되었으나, 6%의 고농도에서는 중첩곡선에서 벗어나는 현상을 보였다. 펙틴 용액의 점탄성을 조사한 결과 전 농도범위에서 손실탄성률$(G^{\prime\prime})$의 값이 저장탄성률$(G^\prime)$보다 훨씬 높은 값을 보여 점성이 전체 점탄성을 지배하는 것으로 나타났다. 저 농도에서 전단점도는 복소점도와 거의 비슷한 값을 보여 Cox-Merz 법칙에 잘 부합하였으나, 농도가 높아질수록 두 값은 차이를 보였다.

• 한국식품영양과학회지
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• 제46권5호
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• pp.608-615
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• 2017

본 연구는 국산 신품종 감자인 '고운', '새봉', '진선'의 이화학적, 구조적 및 유변학적 특성을 도입 품종인 '대서'와 비교하여 측정함으로써 신품종 감자의 가공적성 규명과 가공식품 제조를 위한 기초자료를 마련하기 위해 수행되었다. 감자가루의 총전분 함량은 도입 품종인 '대서'에서 73.34%로 유의적으로 가장 높게 나타났다. 품종별 감자가루의 인 함량은 '새봉'에서 2,249.94 ppm으로 가장 높게 나타났다. 신품종 감자가루의 구조분석 결과 전분 입자에 비전분성 물질이 결합 혹은 자유롭게 존재하는 미세구조를 나타내었고, X-선 회절도 분석에서 B형 전분의 결정형 피크를 나타내었다. FT-IR 분석 결과 지문영역에서 품종 간에 차이가 나타나지 않아 '대서'와 신품종 감자의 구조적인 특성에는 차이가 없는 것으로 나타났다. Rapid Visco Analyzer에 의한 페이스팅 특성은 '새봉' 품종의 peak viscosity가 유의적으로 높게 나타났으며, setback viscosity는 신품종 감자(38.67~56.00 cP)가 '대서(72.00 cP)'보다 낮게 나타났다. 정상유동 특성은 '대서'의 점조도 지수와 겉보기 점도가 가장 높게 나타났으며, 동적 점탄 특성에서는 진동수가 증가함에 따라 저장 탄성률(G′)과 손실 탄성률(G″) 값이 증가하는 경향을 나타내었으며, '진선'의 G′, G″과 복소 점도 값이 가장 높게 나타났다.

• 한국축산식품학회지
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• 제35권2호
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• pp.156-163
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• 2015

The effects of low molecular-weight collagen peptides derived from porcine skin were investigated on the physicochemical and sensorial properties of chocolate ice cream. Collagen peptides less than 1 kDa in weight were obtained by sub-critical water hydrolysis at a temperature of $300^{\circ}C$ and a pressure of 80 bar. Ice cream was then prepared with gelatin powder and porcine skin hydrolysate (PSH) stabilizers mixed at seven different ratios (for a total of 0.5 wt%). There was no significant difference in color between the resulting ice cream mixtures. The increase in apparent viscosity and shear thinning of the ice cream was more moderate with PSH added than with gelatin. Moreover, the samples containing more than 0.2 wt% PSH had enhanced melting resistance, while the mixture with 0.2 wt% PSH had the lowest storage modulus at $-20^{\circ}C$ and the second highest loss modulus at 10℃, indicating that this combination of hydrocolloids leads to relatively softer and creamier chocolate ice cream. Among the seven types of ice creams tested, the mixture with 0.2 wt% PSH and 0.3 wt% gelatin had the best physicochemical properties. However, in sensory evaluations, the samples containing PSH had lower chocolate flavor scores and higher off-flavor scores than the sample prepared with just 0.5 wt% gelatin due to the strong off-flavor of PSH.