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RISS 인기검색어
- 검색키워드
- 주제어 : characteristic relaxation time (검색결과 6 건)
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Stadler, Florian J.,Mahmoudi, Tahmineh 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.4
In this paper, we assess the frequency dependent rheological data of several different linear and short-chain branched metallocene catalyzed polyethylenes with respect to the description of the viscosity functions. The aim is to derive material specific relaxation time ${\lambda}$ from the fit. This characteristic relaxation time follows a similar dependence to the molar mass $M_w$ as the zero shear-rate viscosity, but slightly depends on both molar mass distribution and comonomer content. The transition between the shear-thinning region and the terminal regime is broader for mHDPE than for mLLDPE and widens with increasing molar mass $M_w$. This finding is explained by the differences in the plateau modulus $G_N^0$ and the increase of the normalized terminal relaxation time in comparison to the characteristic relaxation time, respectively.
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슈타들러,Tahmineh Mahmoudi 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.4
In this paper, we assess the frequency dependent rheological data of several different linear and short-chain branched metallocene catalyzed polyethylenes with respect to the description of the viscosity functions. The aim is to derive material specific relaxation time l from the fit. This characteristic relaxation time follows a similar dependence to the molar mass M_w as the zero shear-rate viscosity, but slightly depends on both molar mass distribution and comonomer content. The transition between the shear-thinning region and the terminal regime is broader for mHDPE than for mLLDPE and widens with increasing molar mass Mw. This finding is explained by the differences in the plateau modulus G_N^0 and the increase of the normalized terminal relaxation time in comparison to the characteristic relaxation time, respectively.
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Evaluation of relaxation spectra of linear, short, and long-chain branched polyethylenes
Florian J. Stadler,Tahmineh Mahmoudi 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.1
The frequency dependent rheological data of several different linear, short- and long-chain branched metallocene catalyzed polyethylenes are assessed with respect to the relaxation spectra. For linear mLLDPEs with Mw/Mn≈ 2, a “master spectrum” is established by normalizing on the molar mass. For samples with a distinctly different molar mass distribution, deviations from the “master spectrum” can be observed. It is also demonstrated how the long-chain branches in polyethylenes of different structure influence the spectrum. Depending on the length of branches in long chain branched materials, it is shown that an increasing in the degree of long-chain branching can be clearly observed in the slow relaxation modes, while the fast ones are only affected by high degrees of long-chain branching.
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Evaluation of relaxation spectra of linear, short, and long-chain branched polyethylenes
Stadler, Florian J.,Mahmoudi, Tahmineh 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.1
The frequency dependent rheological data of several different linear, short- and long-chain branched metallocene catalyzed polyethylenes are assessed with respect to the relaxation spectra. For linear mLLDPEs with $M_w/M_n{\approx}2$, a "master spectrum" is established by normalizing on the molar mass. For samples with a distinctly different molar mass distribution, deviations from the "master spectrum" can be observed. It is also demonstrated how the long-chain branches in polyethylenes of different structure influence the spectrum. Depending on the length of branches in long chain branched materials, it is shown that an increasing in the degree of long-chain branching can be clearly observed in the slow relaxation modes, while the fast ones are only affected by high degrees of long-chain branching.
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THERMAL WAVE CHARACTERISTICS IN A FINITE MEDIUM
Woo-nam Juhng,Yong-ho Lee,Bo-young Choi,Donghwan Lee 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.9
Fourier's law of heat conduction has been applied in solving conduction problems encountered in practice. This law predicts instantaneous heat diffusion with infinite propagation speed. Some recent experiments show the reflections of thermal waves at the interface of dissimilar materials at cryogenic temperature. In situations involving transient heat flow in very short time or at cryogenic temperature, the effects of finite speed of heat propagation become important. The thermal wave characteristics of damping and resonance are derived from the thermal wave equation through both modified heat flux equation and energy conservation law. The thermal resonance and phase lags of heat flux in a finite medium with thermal relaxation time are studied in this work by Finite Fourier transform with respect to space. As the result of the transformation with respect to space, the resonance and phase lags on underdamped condition are found when the modal frequencies in the medium exceed a critical value. The relationship between the modal frequencies and the resonance frequencies is obtained.
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정대훈,황세준,오율권 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.1
Both two laser beams and a digital timer system were used to accurately measure the terminal velocity of a falling ball in the viscometer. In this study, the apparent viscosity and the characteristic relaxation time of the aqueous polyacrylamide Seperan AP-273 solution using the falling ball viscometer were determined. The characteristic relaxation time increased as the polyacrylamide concentration increased. In the Powell-Eyring model, the largest characteristic time was predicted among the tested rheological models. The PIV system was employed to visualize the flow phoenmena around balls.
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