• The Korean Journal of Rheology
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• v.10 no.4
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• pp.227-233
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• 1998

The effects of 1 mol% N-benzylpyrazinium hexafluoroantimonate(BPH) as a thermal latent initiator and blend compositions composed of cycloaliphatic and DGEBA epoxies were investigated in the rheological properties and cure kinetics. Latent properties were performed by measurement of the conversion as a function of reaction time using isothermal DSC at $150^{\circ}C$ and $50^{\circ}C$ Rheological properties of the blend systems were investigated in terms of isothermal experiments using a rheometer. The gelation time was obtained from the evaluation of storage modulus (G'), loss modulus (G") and damping factor (tan$\delta$)). Cross-linking activation energy ($E_c$) was also determined from the Arrhenius equation based on gel time and curing temperature. As a result, the gel time and cross-linking activation energy increased with increasing DGEBA composition. The cure activation energies ($E_a$) were obtained by Kissinger method using dynamic DSC thermograms. In this work, the cure activation energy decreased with increasing CAE concentration, which might be resulted from the short repeat units, simple side-groups and viscosity of reaction media.edia.

• Polymer(Korea)
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• v.25 no.1
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• pp.15-24
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• 2001

In this study, the effects of different glycol molar ratios of unsaturated polyester(UPE) resins on the curing behaviors were investigated. The cross linking process was checked or monitored by differential scanning calorimetry(DSC) and by viscoelastic properties of rigid-body pendulum model. The knife-edge from which the pendulum is suspended, is immersed in a reaction mixture, and the change of the viscoelastic behavior brings on those of the period(T) and logarithmic decrement(${\Delta}$) of the damped free oscillations of the pendulum. The values of T and ${\Delta}$ obtained are related to the dynamic modulus(E') and modulus loss(E'). The information on the viscoelastic behavior of unsaturated polyester(UPE) resins during the curing process are shown to illustrate the usefulness of the techniques. As the content of NPG in a propylene glycol(PG)/NPG glycol mixture increased, both the cycle time during cure and the change of damping during cure of UPE resin decreased.

• Restorative Dentistry and Endodontics
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• v.29 no.6
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• pp.489-497
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• 2004

Objective: The purpose of this study was to investigate the viscoelastic properties related to handling characteristics of composite resins, Methods: A custom designed vertical oscillation rheometer (VOR) was used for rheological measurements of composites. The VOR consists of three parts: (1) a measuring unit, (2) a deformation induction unit and (3) a force detecting unit, Two medium viscous composites, Z100 and Z250 and two packable composites, P60 and SureFil were tested. The viscoelastic material function, including complex modulus $E^{*}$ and phase angle ${\delta}$, were measured. A dynamic oscillatory test was used to evaluate the storage modulus (E'), loss modulus (E") and loss tangent ($tan{\delta}$) of the composites as a function of frequency ($\omega$) from 0.1 to 20 Hz at $23^{\circ}C$. Results: The E' and E" increased with increasing frequency and showed differences in magnitude between brands. The $E^{*}s$ of composites at ${\omega}{\;}={\;}2{\;}Hz$, normalized to that of Z100, were 2.16 (Z250), 4,80 (P60) and 25.21 (SureFil). The magnitudes and patterns of the change of $tan{\delta}$ of composites with increasing frequency were significantly different between brands. The relationships between the complex modulus $E^{*}$, the phase angle ${\delta}$ and the frequency \omega were represented by frequency domain phasor form, $E^{*}{\;}(\omega){\;}={\;}E^{*}e^{i{\delta}}{\;}={\;}E^{*}{\angle}{\delta}$. Conclusions: The viscoelasticity of composites that influences handling characteristics is significant different between brands, The VOR is a relatively simple device for dynamic, mechanical analysis of high viscous dental composites. The locus of frequency domain phasor plots in a complex plane is a valuable method of representing the viscoelastic properties of composites.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.700-703
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• 2003

The test method of ASTM E 756 and KS D 0076 to estimate vibration-damping properties is compared. Comparison method depending on specimen support, exciting method and calculation method for loss factor is used. Half-power bandwidth method and vibration decay method is used in the calculation method for loss factor, and Young's modulus is decided by geometric character and density for specimen and resonance frequency. Vibration measurement sensor is compared by using non-contact displacement detector, velocity detector and accelerometer. This paper is also presented the matter which is able to cause error in the measurement

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.439-442
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• 2003

The test method of ASTM E 756 and JIS G 0602 to estimate vibration-damping properties is presented. Measurement method depending on specimen support, exciting method and calculation method for loss factor is used. Half-power bandwidth method and vibration decay method is used in the calculation method for loss factor, and Young's modulus is decided by geometric character and density for specimen and resonance frequency. Vibration measurement sensor is compared by using non-contact displacement detector, velocity detector and accelerometer. The cause of measurement error is also presented.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.377-383
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• 2011

Thermoelectric power, dc conductivity, and the dielectric relaxation properties of $La_2NiO_{4.03}$ are reported in the temperature range of 77 K - 300 K and in a frequency range of 20 Hz - 1 MHz. Thermoelectric power was positive below 300K. The measured thermoelectric power of $La_2NiO_{4.03}$ decreased linearly with temperature. The dc conductivity showed a temperature variation consistent with the variable range hopping mechanism at low temperatures and the adiabatic polaron hopping mechanism at high temperatures. The low temperature dc conductivity mechanism in $La_2NiO_{4.03}$ was analyzed using Mott's approach. The temperature dependence of thermoelectric power and dc conductivity suggests that the charge carriers responsible for conduction are strongly localized. The relaxation mechanism has been discussed in the frame of the electric modulus and loss spectra. The scaling behavior of the modulus and loss tangent suggests that the relaxation describes the same mechanism at various temperatures. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with activation energy of ~ 0.106eV. At low temperature, variable range hopping and large dielectric relaxation behavior for $La_2NiO_{4.03}$ are consistent with the polaronic nature of the charge carriers.

• The Journal of the Acoustical Society of Korea
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• v.21 no.1E
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• pp.12-17
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• 2002

Two improvements are discussed in measurement of the complex Young's modulus of the acoustic materials by using the transfer function method. It is found that the accelerometer misalignment might result in the severe measurement error, particularly in high frequency range. The supporting structure is modified to attach the upper and lower accelerometers along the vertical axis. Secondly, the method fur solving the equation associated with wave model is described. The solution of the lumped mass-spring model is chosen as the starting value for low frequency range, while in the mid and high frequency, the solution to the previous frequency step is used as the initial values. Measurements are done for hard and soft rubber specimens. It is shown that the erroneous peaks in the transfer function, due to the measurement error, cause highly incorrect Young's modulus and loss factors.

• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.E
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• pp.60-69
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• 1992

The research significance of the paper is to identify the major properties of synthetic lightweight concrete that are affected by ASR expansion and to determine the extent and magnitude of the loss in these properties. Emphasis is also given to the use of non-destructive testing techniques ; Such as dynamic modulus of elasticity and ultrasonic pulse velocity, to examine whether these methods could be used to identify the initiation of expansion and the internal structural damage caused by ASR.

• Elastomers and Composites
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• v.25 no.2
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• pp.97-102
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• 1990

Linear viscoelastic properties of 11 types of EPDM and 1 type of EPM rubbers have been measured at $210^{\circ}C$, using a RDS(Rheometrics dynamic spectrometer). The data base, i.e., complex viscosity, storage modulus, loss modulus, loss tangent and relaxation spectrum of the sample should be useful for rubber blending and compounding.

• Journal of the korean Society of Automotive Engineers
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• v.16 no.4
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• pp.32-36
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• 1994

본 연구에서는 제진재의 최적화를 수행하기 위한 선행 단계로써 제진재 모델링에 필요한 제진재 물성치 산출법과 모델링 기법을 확립하였다. 1. 제진재 물성치(Loss factor ; .eta., Young's Modulus; E) 산출이론. 2. 실험을 통한 제진재 물성치 산출. 3. 제진재 모델링 방법 및 실험과의 비교.