• Journal of the Korean Magnetics Society
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• v.15 no.5
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• pp.261-264
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• 2005

The elastic constants, C', of $Th_{3}P_4$-type structure compounds, $La_{3}S_4\;and\;Ce_{3}S_4$, have been analyzed on the basis of band Jahn-Teller mechanism. The distinct difference between two compounds lies in the fact that $Ce^{3+}$ ion has a f electron which produces magnetism. It is shown that the band Jahn-Teller effect is sensitively influenced by the energy splitting of f electronic bands by a cubic crystal field in $Ce_{3}S_4$, and f electrons suppress the elastic softening effect. The energy splitting value obtained from the calculation of elastic constants is found to agree well with the experimental value obtained from the magnetic susceptibility measurement.

• Tunnel and Underground Space
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• v.18 no.4
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• pp.252-262
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• 2008

In the uniaxial compressive test of a single specimen of transversely isotropic rock, its 5 independent elastic constants can not be defined since maximum 4 independent strain measurements are available theoretically. In order to solve this problem, one equation proposed by Saint Venant in 19C and confirmed by Lekhnitskii through the test experiences has been used for long time. Accordign to authors' experiences, however, this equation turned out to give erroneous elastic constants in some cases. Three new equations are suggested and their compatibilities are discussed in this paper. As the results of the analyses of the models, Lekhnitskii's suggested equation is effective for the specimen with the high dip angle whereas it results in the large erred output for that with dip angle less than $25{\sim}30$. It was found that the effectivenesses of three suggested equations and their compatibilities are subject to the dip angle and not to the amounts of elastic constants. Guide map to the selection of the compatible one of those suggested equations is presented as a result of the study.

• The Journal of the Acoustical Society of Korea
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• v.23 no.2
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• pp.103-108
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• 2004

In this paper, all the materials constants of the PMN-32%PT single crystals grown by the solid state crystal growth method were measured by the resonance method. PMN-PT crystals of tetragonal symmetry have six elastic constants, three piezoelectric constants and two dielectric constants for their independent material constants. These materials constants were extracted from six sets of crystal samples of each different geometry to have different vibration modes respectively. Measured results showed that the crystal has larger electromechanical coupling factor k/sub 33/ (∼86%) and piezoelectric constant d/sub 33/ (∼1200pC/N) than conventional piezoceramics. Validity of the measurement was confirmed through comparison of the results with the impedance spectrum from finite element analysis of the samples and the results measured with a commercial do meter.

• Journal of the Mineralogical Society of Korea
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• v.17 no.3
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• pp.201-208
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• 2004

$CaSiO_3$-garnet phase was observed in the phase transformation sequences on a natural hedenbergite, (Ca, Fe)$ SiO_3$ between 14 and 24 GPa when quenched from $～1200^{\circ}C$. Bulk modulus K = 155 GPa, $V_{\Phi}$ = 6.58 km/sec and other elastic properties of the $CaSiO_3$-garnet were obtaiend on the basis of the systematics of structural analogs in varius garnet phases and relationship of $KV_{m}$ = constant and $V_{\Phi}$$M^{$\frac{1}{2}$}$ = constant. The quenchable garnet phase apears to be stabilized by the considerable amount of Mn and other cations, and shows a wide stability range. As one of the host minerals of Ca composition, $CaSiO_3$-garnet would be one of the important mineral phases in the mantle transition region.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.96-105
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• 1995

A modified method for the analysis of short fatigue crack growth has been presented, and calculations based upon the modified method are compared with experimental results for S45C carbon steel. It is also shown that the modified method is in good agreement with experimental data. The proposed equation for the fatigue crack growth rates includes a material constant which relates the threshold level to the endurance limit, a correction for elastic-plastic behaviour and a means for dealing with the effects of crack closure. In this study one of the modifications is to substitute the Forman' s elastic expression of the stress intensity factor range into the geometrical factor The other is a consideration of the bending effect which is developed from the moment caused by the eccentric cross sectional geometry as the crack grows. Thus, this method is useful for residual life prediction of the mechanical structures as well as the welding structures.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1315-1321
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• 2005

Using hyper-elastic material has been increased gradually and its range was extended all over the industrial. In addition, the performance prediction of this material was required not only experimental methods like metal material but also numerical methods. In this study, we presented the process how to use numerical method for hyper-elastic material and then, it was applied for seat-ring of butterfly valve by using this process. The finite element analysis was executed to evaluate the mechanical characteristics of hyper-elastic material and search the optimum model considered conditions and features. According to that model the coefficient was obtained by using Contact analysis.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.291-292
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• 2012

MOSFET 구조에서 metal oxide에 기반을 둔 게이트 유전체의 연구는 실리콘(Si)을 기반으로 한 반도체 발명이래로 가장 인상적인 발전을 이뤄 왔다. 이는 metal oxide의 높은 유전상수 특성이 $SiO_2$보다 우수하고, 유전체 박막의 두께 감소로 인한 전기적 특성 저하를 보완하기 때문이다. 특히 지난 10년 동안, Hafnium에 기반을 둔 $HfO_2$는 차세대 반도체용 유전 물질로 전기적 구조적 특성에 대한 연구가 활발히 진행되어왔다. 그러나 현재까지 $HfO_2$에 대한 nano-mechanical 특성 연구는 미미하여 이에 대한 연구가 필요하다. 이에 본 연구에서는 Hf 및 $HfO_2$ 박막의 증착 및 열처리 조건을 다르게 하여 실험을 진행하였다. 시료는 rf magnetron sputter를 이용하여 Si 기판위에 Hafnium target으로 산소유량(4, 6 sccm)을 달리하여 증착하였고, 이후 furnace에서 400에서 $800^{\circ}C$까지 질소분위기에서 20분간 열처리를 실시하였다. 실험결과 산소 유량을 6 sccm으로 증착한 시료의 current density 성능이 모든 열처리 과정에서 증가하였다. Nano-indenter로 측정하고 Weibull distribution으로 정량적 계산을 한 경도 (Hardness)는 as-deposited 시료를 기준으로 $400^{\circ}C$에서는 감소했으나 온도가 높아질수록 증가하였다. 특히, $400^{\circ}C$ 열처리한 시료에서 산소농도에(4 sccm : 5.35 GPa, 6 sccm : 6.15 GPa)따른 두 시료간의 변화가 가장 두드러졌다. 반면에, 탄성계수 (Elastic modulus)는 산소농도 6 sccm을 넣고 증착된 시료들이 4 sccm을 넣고 증착한 시료보다 모두 높은 값을 나타냈다. 또한, $800^{\circ}C$ 열처리한 시료에서 산소농도에(4 sccm : 128.88 GPa, 6 sccm : 149.39 GPa)따라 표면의 탄성에 큰 차이가 있음을 확인하였다. 이는 증착된 $HfO_2$ 시료들이 비정질 상태에서 $HfO_2$로 결정화되는 과정에서 산소가 증가할수록 박막의 defect이 감소되기 때문으로 사료된다.

• Elastomers and Composites
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• v.43 no.3
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• pp.173-182
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• 2008

Rubber-pad forming process for materials such as metal in which portions of the die which act upon the material is composed of a natural or synthetic rubber or elastomer material. This makes the rubber pad forming process relatively cheap and flexible, high accuracy for small product series in particular. In this study, we carried out the physical test and finite element analysis of elastomer such as natural rubber and urethane for steel rack rube forming. The non-linear property of elastomer which are described as strain energy function are important parameter to design and evaluate of elastomer component. These are determined by material tests which are uni-axial tension and bi-axial tension. This study is concerned with simulation and investigation of the significant parameters associated with this process.

• Polymer(Korea)
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• v.24 no.2
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• pp.259-267
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• 2000

Gel polymer electrolytes were prepared from poly(vinylidene fluoride-co-hexafluoro propylene)[P(VdF-co-HFP)] that had higher mechanical properties as well as higher dielectric constant ($\varepsilon$=8~13) than other polymeric matrix. Mechanical properties and ionic conductivities have been investigated as a function of blend ratio of electrolyte solution and polymer matrix. Ethylene carbonate (EC)/${\gamma}$-butyrolactone (${\gamma}$-BL) and lithium triflate (LiCF$_3$SO$_3$) were used as solvent and salt, respectively. The mechanical properties such as tensile strength, tensile modulus, compression modulus, and dynamic shear modulus were evaluated. The highest ionic conductivity was 1.09$\times$10$^{-3}$ S/cm for PVH40 containing 28.6 wt% of P(VdF-co-HFP) at $25^{\circ}C$. Tensile strength, tensile modulus and compression modulus were increased with P(VdF-co-HFP) content and abruptly changed between PVH70 and PVH80. Dynamic shear moduli showed a typical gel behavior and changed with shear strain.

• Korean Journal of Food Science and Technology
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• v.34 no.5
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• pp.830-834
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• 2002

본 연구는 동적 전단진동(dynamic shear oscillation) 측정방법을 이용하여 농도가 젤라틴의 동적 레올로지 특성에 미치는 영향에 대하여 관찰하였다. $5^{\circ}C$에서의 젤라틴의 저장 탄성률(storage modulus, G#)과 손실 탄성률(loss modulus, G@)은 농도가 증가함에 따라 증가하는 경향을 보였다. 0.9%를 제외한 모든 농도(2.0-4.9%)에서 젤라틴의 G#은 G@보다 매우 높은 값을 나타냈으며, G#과 G@이 ${\omega}$ 의존성이 없는 true 겔과 같은 거동을 나타냈다. 젤라틴의 농도와 K#(G#에 대한 절편)와의 관계에서는 높은 결정계수$(R^2=0.99)$를 보여주면서 좋은 상관관계를 나타냈다. 여러 온도범위$(-5,\;0,\;5,\;10^{\circ}C)$에서 각 온도별로 측정된 K#값은 $-5^{\circ}C(59.5Pa)\;>\;0^{\circ}C(4.09Pa)\;>\;5^{\circ}C(1.41Pa)\;>\;10^{\circ}C(0.35Pa)$의 순으로 가장 낮은 온도에서 K#값이 가장 높은 것으로 나타났다. 또한 냉각과정에서 최종냉각온도인 $5^{\circ}C$에서 측정된 젤라틴의 최대 G#수치는 4.9%(2399Pa)>4.1%(1744Pa)>3.0%(1159Pa)>2.0%(519.3Pa)>0.9%(3.15Pa)의 순으로 높은 농도에서 높게 나타났다. Aging 10시간 동안 젤라틴 겔의 구조형성은 겉보기 first-order kinetics로부터 겉보기 구조형성 속도상수(K)를 결정함으로써 파악될 수 있다. 젤라틴의 농도가 증가함에 따라 K값은 증가하였으며, 농도와 K값과의 관계는 높은 결정계수$(R^2)$를 나타내면서 좋은 상관관계를 보여주었다(Fig. 7). 10시간 aging 후 G#은주파수$({\omega})$ 의존성이 없이 독립적인 것으로 나타났다. 따라서 이들 젤라틴 겔은 aging하는 동안에 탄성이 점점 강해지고 10시간 후에는 가교결합의 밀도가 증가하여 강한 탄성을 가진 고무질 망상구조(rubber network)를 형성했음을 알 수 있다.