• Macromolecular Research
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• 제14권3호
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• pp.365-372
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• 2006

Poly[styrene-b-(ethylene-co-butylene)-b-styrene](SEBS) triblock copolymer was studied by dissolving the ethylene butylene midblock in selective hydrocarbon oils. These oils differ in their aromatic, paraffinic and naphthenic content. Dynamic rheological studies showed that the storage modulus (G') exceeded the loss modulus (G') for all the gels over the entire range of frequency, thereby confirming them as physical gels. However, the behavior of G' and G' as a function of frequency depended primarily on the oil type. The gelation melting temperature decreased drastically with increased oil aromaticity. Small angle X-ray scattering studies revealed that the maximum interdomain interference shifted to a higher angle depending on the composition and type of hydrocarbon oil.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 1997년도 추계총회 및 학술발표회 논문집
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• pp.126-130
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• 1997

A series of Thermoplastic polyurethane elastomers was prepared via a two-step polymerization process. The NCO/OH feed ratio of polyurethane synthesized in this study was varied from 1 to 1.3. Studies have been made on the effects of chemical and physical cross-linkina, and the properties of thermoplastic polyurethane elastomers based on isophorone diisocyanate (IPDI)/1,4-butanediol (BD)/poly(propylene glycol) (PPG, MW:2000), isophorone diisocyanate (IPDI)/BD /poly(oxytetramethylene) glycol (PTMG, MW:2000) was compared. These materials were characterized using FTIR spectrometer, dynamic mechanical thermal analyzer, and tensile retraction tester. PTMG based polyurethane elastomers showed higher elasomeric behavior than PPG based polyurethane elastomers at the same NCO/OH ratio. This feature has been connected with the specific nature of the polyols. The permanent set(%) was decreased with increasing maximum elongation from 50% to 300%.

• Smart Structures and Systems
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• 제23권5호
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• pp.429-447
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• 2019

The present study analyzed free vibration of the three-layered micro annular/circular plate which its core and face sheets are made of saturated porous materials and FG-CNTRCs, respectively. The structure is subjected to magneto-electric fields and magneto-electro-mechanical pre loads. Mechanical properties of the porous core and also FG-CNTRC face sheets are varied through the thickness direction. Using dynamic Hamilton's principle, the motion equations based on MCS and FSD theories are derived and solved via GDQ as an efficient numerical method. Effect of different parameters such as pores distributions, porosity coefficient, pores compressibility, CNTs distribution, elastic foundation, multi-physical pre loads, small scale parameter and aspect ratio of the plate are investigated. The findings of this study can be useful for designing smart structures such as sensor and actuator.

• Steel and Composite Structures
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• 제46권5호
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• pp.637-647
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• 2023

Nonlinear free vibration and stability responses of a carbon nanotube reinforced composite beam under temperature rising are investigated in this paper. The material of the beam is considered as a polymeric matrix by reinforced the single-walled carbon nanotubes according to different distributions with temperature-dependent physical properties. With using the Hamilton's principle, the governing nonlinear partial differential equation is derived based on the Euler-Bernoulli beam theory. In the nonlinear kinematic assumption, the Von Kármán nonlinearity is used. The Galerkin's decomposition technique is utilized to discretize the governing nonlinear partial differential equation to nonlinear ordinary differential equation and then is solved by using of multiple time scale method. The critical buckling temperatures, the nonlinear natural frequencies and the nonlinear free response of the system is obtained. The effect of different patterns of reinforcement on the critical buckling temperature, nonlinear natural frequency, nonlinear free response and phase plane trajectory of the carbon nanotube reinforced composite beam investigated with temperature-dependent physical property.

• 공업화학
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• 제24권2호
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• pp.214-218
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• 2013

나일론66에 다중벽 탄소나노튜브(multi-walled carbon nano tube, MWCNT)를 1, 3, 5, 7 wt% 첨가하여 이축압출기(twin screw extruder)를 이용하여 나일론66/MWCNT 복합체를 제조하였다. MWCNT의 함량에 따른 열적특성, 분산성, 유변 학적 특성 및 충격특성을 DSC, TGA, X선 회절 분석기(XRD), 전자주사현미경(SEM), 동적유변측정기(ARES) 그리고 Izod 시험기를 이용하여 분석하였다. 나일론66에 MWCNT를 첨가할 때 나일론66의 비등온결정화에 영향을 주는 것을 DSC를 이용하여 확인하였다. 나일론66/MWCNT 복합체의 경우 낮은 전단속도 영역에서 복합점도 및 복합점도에 대 한 주파수 의존성을 나타내는 전단박하(shear thinning)가 증가하였으며, MWCNT 함량이 증가할수록 증가폭이 크게 나타났다. 또한 복합체의 G'-G" plot의 기울기가 감소하는 현상으로부터 탄성특성 증가를 확인하였다. 기계적 물성으 로 Izod 충격강도를 분석하였고, 3 wt% MWCNT가 첨가될 때 60%의 충격강도 개선을 확인하였다. SEM을 이용하여 나일론66내의 MWCNT의 분산성을 확인하였다.

• Elastomers and Composites
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• 제35권3호
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• pp.173-179
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• 2000

3가지 대표적인 가황계인 conventional vulcanization(Conv), semi-efficient vulcanization (Semi-EV), efficient vulcanization(EV)방법을 카본블랙 충전 천연고무 배합고무에 대해 적용하고, 이들 가황계에 따른 가황특성, 인장특성, 동적 점탄성을 조사하였다. 또한 가황온도가 배합고무의 기계적 물성과 노화저항성에 미치는 영향도 조사하였다. Conv 가황계가 Semi-EV나 EV 가황계에 비해 가황속도는 낮았으나 최대 토오크는 높았다. 인장특성은 Conv 가황계가 Semi-EV나 EV 가황계에 비해 높은 모듈러스를 나타내었고, 파괴점에서의 인장강도는 유사한 반면 신장율은 낮았다. 가황온도 증가에 따라 경도, 모듈러스 및 인장강도는 감소하였고, 감소 정도는 EV나 Semi-EV 가황계가 Conv 가황계보다 낮았다. 또한 열노화에 대한 저항성은 EV 가황계가 Conv 가황계보다 월등히 우수하였다.

• International Journal of Concrete Structures and Materials
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• 제18권2E호
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• pp.117-124
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• 2006

Porous concrete has been used recently for the purpose of decreasing the load on the earth environment. It consists solely of cement, water and coarse aggregate of uni form size. Its fundamental properties are considerably affected by the physical properties of aggregate because the aggregate is the main material for the most part in its mix proportion. Because of this reason, this study carried out an investigation of the influence of the size and type of aggregate on the fundamental properties of porous concrete. It is shown that the fundamental properties of porous concrete was seldom affected by the size of aggregate except for the case of using $2.5{\sim}5mm$ aggregate but varied significantly by the type of aggregate. In particular, the compressive strength of porous concrete using $2.5{\sim}5mm$ aggregate was much higher than that using other aggregate, and its void ratio and coefficient of permeability was lower. Moreover, the capacity to maintain the permeability of porous concrete was found to vary by the size and type of aggregate. Of particular notice was that it decreased greatly when $2.5{\sim}5mm$ aggregate was used. Unlike ordinary concrete, porous concrete exhibited very high dynamic modulus of elasticity at early age and continued to increase but slowly afterwards.

• 한국세라믹학회지
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• 제32권6호
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• pp.748-760
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• 1995

Pyroelectric properties, figure of merits, and the other properties of the Pb(Zn1/3Nb2/3)O3-Pb(Fe1/2Nb1/2)O3 system, as expected to have excellent pyroelectric properties in the operating temperature range of pyroelectric type infrared sensor, were investigated. In the Pb(Zn1/3Nb2/3)O3-Pb(Fe1/2Nb1/2)O3 system, suppression of the pyrochlore phase depended on sintering condition, as like sintering temperature, holding time, sintering atmosphere. The specimen, sintered by the same composition atmosphere powder at 105$0^{\circ}C$ for 1.5h, possessed the best physical property. It was found that the piezoelectric parameters were mainly depended on the amount of spontaneous polarization and then the 0.2PZN-0.8PFN showed the best pyro- and piezoelectric properties. In terms of the experimental method, two pyroelectric-testing methods, i.e. static and dynamic methods, had a same tendency. Also the result of pyroelectric testing by the static method indicated that the diffuse phase transitiion resulted in the temperature difference of phase transition between dielectric constant and pyroelectric coefficient.

• Geomechanics and Engineering
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• 제17권3호
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• pp.261-270
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• 2019

Because the estimation of the tensile strength is very important in any geotechnical project, many attempts have been made to determine. But the immediate determination of the tensile strength is usually difficult owing to well-shaped specimens, time-consuming, expensive and sometimes unreliable. In this study, engineering properties of several ultramafic rock samples were measured to assess the correlations between the Brazilian Tensile Strength (BTS) and degree of serpentinization, physical, dynamic and mechanical characteristics. For this purpose, a comprehensive laboratory testing program was conducted after collecting thirty-two peridotite and fifty-one serpentinite rock samples, taken from central Greece, in accordance with ASTM and ISRM standards. In addition, a representative number of them were subjected to petrographic studies and the obtained results were statistically described and analysed. Simple and multiple regression analyses were used to investigate the relationships between the Brazilian Tensile Strength and the other measured properties. Thus, empirical equations were developed and they showed that all of the properties are well correlated with Brazilian Tensile Strength. The curves with the $45^{\circ}$ line (y = x) were extracted for evaluating the validity degree of concluded empirical equations which approved approximately close relationships between Brazilian Tensile Strength and the measured properties.

• 폴리머
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• 제26권3호
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• pp.335-343
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• 2002

블렌드 (PET/PETG 70/30 블렌드) 수지는 폴리에틸렌테레프탈레이트 (PET)와 폴리에틸렌테레프탈레이트 글리콜 (PETG)을 무게 비 70/30으로 혼합하여, 이축 압출기를 사용하여 제조하였다. 미연신 필름은 이 블렌드와 순수 PETG 수지를 압축성형기로 각각 용융 압축시켜 제조하였고 연신 필름은 미연신 필름을 모세관 레오메타를 사용하여 연신시켜 제조하였다. 제조된 블렌드 연신 필름과 PETG 연신 필름의 결정성, 수축율, 열적, 동역학적 및 기계적 특성을 X-선 회절분석기, 오븐기, DSC, 및 인장시험기를 사용하여 조사하였다. 블렌드와 PETG필름의 결정화도와 밀도는 연신비와 연신 속도의 증가와 더불어 증가하였으나 반면 연신 온도 증가와 더불어 감소하였다 또한 블렌드 필름의 결정화도와 밀도는 PETG 필름보다 높게 나타났다. 두 필름의 인장강도와 인장탄성률은 연신비 및 연신 속도 증가와 더불어 증가하였고 연신온도 증가에 따라 감소하였다. 또한 블렌드 필름의 인장강도와 인장탄성률이 PETG 필름 보다 높게 나타났다. 두 필름의 수축율은 연신비와 연신 속도가 증가할수록 감소하였고 미연신 블렌드 필름의 수축율이 순수 PET 필름보다 600% 증가함을 보였다.