• Korean Journal of Food Science and Technology
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• v.27 no.2
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• pp.193-198
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• 1995

The changes in the rheological properties of soybean curd upon the various storage temperatures ($5{\sim}25^{\circ}C$) were measured by the stress-relaxation test and analysed by time-temperature superposition theory. As the storage temperature was lower, higher initial and equilibrium stress of soybean curd were observed. When the stress-relaxation curves were moved horizontally by using the shift-factor on the basis of reference temperature, the master curve was obtained. By applying master curve and shift-factor to the WLF (Williams-Landel-Ferry) equation, activation energy (30kcal/mol) was calculated and storage time at the specific temperature could be predicted, suggesting the equivalent shelf-life of soybean curd texture.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.46-51
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• 2019

Intermittent CSR testing was used to investigate the degradation of a NBR O-ring, and also the prediction of its life-time. An intermittent CSR jig was designed taking into consideration the O-ring's environment under use. Degradation of O-rings by thermal aging was observed between $40^{\circ}C$ and $120^{\circ}C$. O-rings showed non-linear degradation behavior under $80^{\circ}C$. At 20% of failure condition, predicted life-times were 32.5 years by Arrhenius plot and 22.6 years by WLF plot.

• Proceedings of the KIPE Conference
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• 2009.11a
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• pp.179-181
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• 2009

고압 방전 램프는 점등 후부터 정상상태에 이르기까지 방전관 내부의 온도 및 압력이 광범위하게 변화하는 복잡한 동작 특성으로 모델링이 어렵다. 이러한 특성은 램프를 구동하는 안정기의 설계에 어려움이 따른다. 램프의 구동에는 초기 점화 시 높은 점화용 전압 펄스를 필요로 한다. 점화 후에 정상상태에 다다르면 램프 전극의 소모를 줄이기 위해 교류로 구동되어야 한다. 하지만 램프를 교류로 구동하게 되면 음향 공진 현상이 발생할 수 있다. 음향 공진 현상은 램프 구동 전류의 맥동성분이 큰 경우에도 발생을 할 수 있으므로 구동 전류의 맥동 성분의 크기는 최소화 돼야 한다. 램프의 수명시간을 길게 하려면, 안정기는 램프를 정격전력으로 구동하여야 한다. 따라서 안정기에서는 정전력 제어가 필요하게 된다. 램프 전류의 극성이 변화할 때, 램프 전류는 spike전류와 중첩이 된다. 본 논문에서는 spike 전류를 저주파구형파 램프 전류의 포락범위 안에 유지하고, 고주파 스위칭시손실을 줄이기 위해 소프트 스위칭 기법을 이용한 회로 설계를 제안했다. 제안된 방법은 시뮬레이션 및 이론적 수식적 방법으로 검증 했다.

• Journal of the Korean Society of Safety
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• v.11 no.4
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• pp.143-150
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• 1996

This is an explicit-Implicit, finite element analysis for linear as well as nonlinear hygrothermal stress problems. Additional features, such as moisture diffusion equation, crack element and virtual crack extension(VCE ) method for evaluating J-integral are implemented in this program. The Linear Elastic Fracture Mechanics(LEFM) Theory is employed to estimate the crack driving force under the transient condition for and existing crack. Pores in materials are assumed to be saturated with moisture in the liquid form at the room temperature, which may vaporize as the temperature increases. The vaporization effects on the crack driving force are also studied. The Ideal gas equation is employed to estimate the thermodynamic pressure due to vaporization at each time step after solving basic nodal values. A set of field equations governing the time dependent response of porous media are derived from balance laws based on the mixture theory Darcy's law Is assumed for the fluid flow through the porous media. Perzyna's viscoplastic model incorporating the Von-Mises yield criterion are implemented. The Green-Naghdi stress rate is used for the invariant of stress tensor under superposed rigid body motion. Isotropic elements are used for the spatial discretization and an iterative scheme based on the full newton-Raphson method is used for solving the nonlinear governing equations.

• International Journal of Highway Engineering
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• v.14 no.5
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• pp.75-83
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• 2012

PURPOSES: Suggestion of asphalt binder constitutive model based on time-temperature superposition principle and overstress concept in order to describe behavior of asphalt binders. METHODS: A series of temperature sweep tests and multiple stress creep and recovery(MSCR) tests are performed to verify the applicability of time-temperature superposition principle(t-Ts) and to develop viscoelastoplastic constitutive equation based on overstress concept. For the tests, temperature sweep tests at various high temperature and various frequency and MSCR test at $58^{\circ}C$, $64^{\circ}C$ $70^{\circ}C$, $76^{\circ}C$, and $82^{\circ}C$ are performed. From the temperature sweep tests, dynamic shear modulus mastercurve and time-temperature shift function are built and the shift function and MSCR at $58^{\circ}C$ are utilized to determine model coefficients of VBO model. RESULTS: It is observed that the time-temperature shift function built at low strain level of 0.1% is applicable not only to 1.0% strain level temperature sweep test but also maximum 500,00% strain level of MSCR test. As well, the modified VBO model shows perfect prediction on MSCR measured strain at the other temperatures. CONCLUSIONS: The Time-temperature superposition principle stands hold from very low strain level to very high strain level and that the modified VBO model can be applicable for various range of strain and temperature region to predict elastic, viscoelastic, and viscoplastic strain of asphalt binders.