• Journal of the Korean Wood Science and Technology
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• v.42 no.3
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• pp.275-281
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• 2014

In this study, accelerated weathering test was performed with wood, a major material for wooden cultural building. In order to evaluate the deterioration of wood, ultrasonic transmission times were measured to evaluate dynamic modulus of elasticity (MOE), which was verified by determining static MOE using three-point bending test. Ultrasonic transmission time was decreased with an increase in the weathering time levels (0, 500, 1000 hours) while it increased in 1500 and 2000 hours. Distribution of dynamic and static MOE was similar to that of the ultrasonic transmission time measurements. The results mean that the measurement of ultrasonic transmission time was very effective to evaluate MOE of wooden cultural buildings for their preservation and management. This method could be utilized to assess wooden cultural buildings as a way of preserving them in a scientific manner.

• Journal of the Korean Geotechnical Society
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• v.18 no.3
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• pp.126-126
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• 2002

In dynamic analyses such as seismic ground response and soil-structure interaction problems, it is very crucial to obtain accurate dynamic shear modulus of soil deposit. In this study, an extensive data base of available experimental data is compiled and reanalyzed to establish a simple empirical formula for the dynamic shear modulus reduction curve to cover wide range of strain for sandy soils. The proposed empirical equation is to represent the dynamic shear modulus degradation with strain in terms of low-amplitude dynamic shear modulus and effective mean confining Pressure, since those factors have the most significant effect on the Position and shape of the shear modulus reduction curve for nonelastic soils. If low-amplitude shear modulus is measured, degraded modulus at any shear strain amplitude can be calculated using the proposed equation.

• Journal of the Korean Geotechnical Society
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• v.18 no.3
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• pp.127-138
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• 2002

In dynamic analyses such as seismic ground response and soil-structure interaction problems, it is very crucial to obtain accurate dynamic shear modulus of soil deposit. In this study, an extensive data base of available experimental data is compiled and reanalyzed to establish a simple empirical formula for the dynamic shear modulus reduction curve to cover wide range of strain for sandy soils. The proposed empirical equation is to represent the dynamic shear modulus degradation with strain in terms of low-amplitude dynamic shear modulus and effective mean confining Pressure, since those factors have the most significant effect on the Position and shape of the shear modulus reduction curve for nonelastic soils. If low-amplitude shear modulus is measured, degraded modulus at any shear strain amplitude can be calculated using the proposed equation.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.109-122
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• 2002

The water content of soil near the ground subgrade varies seasonally, and dynamic deformational characteristics of soil are affected by the variation of water content. Contrary to previous studies which used various specimens of different compaction moisture contents, the influences of water content and capillary Pressure on dynamic deformational characteristics of soil were investigated using the given specimen controlling the matric suction. RC/TS(resonant column and torsional shear) testing equipment was modified so that it can control water content with changing capillary pressure(matric suction). RC/TS tests were performed on subgrade soil collected in the KHC(Korea Highway Corporation) test road. In the field, the cross-hole tests were performed and the water contents were measured at the same site to verify the feasibility and applicability of RC/TS test results. As water content decreased, the tendency of increasing shear moduli in field was well matched with laboratory test results.

• Journal of Korea Foresty Energy
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• v.25 no.2
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• pp.49-54
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• 2006

This study was carried out to provide basic data for using domestic structural softwood lumber efficiently and ensuring structural safety of timber structures. The ratios (k-factor) between static and dynamic MOE measured by ultrasonic device for $2{\times}6$ domestic softwood structural lumber are 1.0602 for Korean red pine, 1.0013 for Korean white pine and 1.2320 for Japanese larch. In machine grade using nondestructive method, 76% of Korean red pine was classified into higher than E9 grade, 85% of Korean white pine was sorted into higher than E7 grade and 68% of Japanese larch was classified into higher than E11 grade. Correlation between MOE and MOR by static bending with k-factor from nondestructive method provide a possibility to predict bending strength and allowable stress of domestic softwood structural lumber.

• Journal of agriculture & life science
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• v.46 no.1
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• pp.35-41
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• 2012

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for woodceramics made by different carbonizing temperature (600, 800, 1000, $1200^{\circ}C$) for Broussonetia kazinoki Sieb. Dynamic modulus of elasticity increased with increasing carbonizing temperature. There was a close relationship of dynamic modulus of elasticity and static bending modulus of elasticity to MOR. Therefore, the dynamic modulus of elasticity using resonance frequency mode is useful as a nondestructive evaluation method for predicting the MOR of woodceramics made by different carbonizing temperature for B. kazinoki Sieb.

• Journal of the KSME
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• v.25 no.1
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• pp.39-46
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• 1985

동적 탄성 파괴역학 문제들을 실험적으로 연구하기 위해서는 우선 빠르게 전파하고 있는 균열 선단(전파속도 V=100m/sec∼1000m/sec for various polymers) 부근의 응력분포 상태나 변위분포 상태등을 기록하는 실험장치가 필수적으로 필요하다. 먼저 Wells와 Post(7)에 의하여 처음으로 사용되었고 Kobayashi(18,19,20)와 Dally(21)등에 의해서 발전, 개선된 동적 광탄성 실험범에 대 하여 설명하고 이 실험에 의하여 동적 응력확대계수를 추출하는 방법을 아울러 강의하고 그의 문제점 등을 논의 하고자 한다.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.2
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• pp.61-69
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• 2011

In this paper, the factors affecting the dynamic characteristics of a polyurethane spring restoring disk bearing are analysed to predict the dynamic behavior of the bearing. The prediction results and the test results are compared. The Young's modulus of the polyurethane spring, which varies according to strain of spring and the friction coefficient, of PTFE (PolyTetraFluoroEthylene), which varies according to the velocity and pressure of PTFE, are considered as the factors influencing the dynamic characteristics. W-PTFE virgin products are used and polyurethane springs are produced for the tests. The equation related to changing the friction coefficient and the modulus of elasticity are obtained through an inverse estimation of the test results. The estimation results, considering the factors affecting the dynamic characteristics, simulate the test results more appropriately than the estimation without the consideration of those factors.

• Restorative Dentistry and Endodontics
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• v.34 no.5
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• pp.450-459
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• 2009

The aim of this study was to measure the initial dynamic modulus changes of light cured composites using a custom made rheometer. The custom made rheometer consisted of 3 parts: (1) a measurement unit of parallel plates made of glass rods, (2) an oscillating shear strain generator with a DC motor and a crank mechanism, (3) a stress measurement device using an electromagnetic torque sensor. This instrument could measure a maximum torque of 2Ncm, and the switch of the light-curing unit was synchronized with the rheometer. Six commercial composite resins [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF)] were investigated. A dynamic oscillating shear test was undertaken with the rheometer. A certain volume ($14.2\;mm^3$) of composite was loaded between the parallel plates, which were made of glass rods (3 mm in diameter). An oscillating shear strain with a frequency of 6 Hz and amplitude of 0.00579 rad was applied to the specimen and the resultant stress was measured. Data acquisition started simultaneously with light curing, and the changes in visco-elasticity of composites were recorded for 10 seconds. The measurements were repeated 5 times for each composite at $25{\pm}0.5^{\circ}C$. Complex shear modulus G*, storage shear modulus G', loss shear modulus G" were calculated from the measured strain-stress curves. Time to reach the complex modulus G* of 10 MPa was determined. The G* and time to reach the G* of 10 MPa of composites were analyzed with One-way ANOVA and Tukey's test ($\alpha$ = 0.05). The results were as follows. 1. The custom made rheometer in this study reliably measured the initial visco-elastic modulus changes of composites during 10 seconds of light curing. 2. In all composites, the development of complex shear modulus G* had a latent period for $1{\sim}2$ seconds immediately after the start of light curing, and then increased rapidly during 10 seconds. 3. In all composites, the storage shear modulus G" increased steeper than the loss shear modulus G" during 10 seconds of light curing. 4. The complex shear modulus of Z1 was the highest, followed by CF, Z2, Z3, TC and DF the lowest. 5. Z1 was the fastest and DF was the slowest in the time to reach the complex shear modulus of 10 MPa.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.175-183
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• 1999

Recently, problems related to vibrations of decomposed granite soils have acquired increasing attention in Korea because those soils cover approximately one third of the country. Both resonant column and cyclic triaxial test were performed to investigate deformation characteristics of unsaturated and cement-mixed decomposed granite soils in Suwon region. The important soil parameters in this respect are the shear moduli, dynamic moduli of elasticity and damping ratios. The dynamic parameters are influenced by variables such as strain amplitude, ratio of loading cycles, and degree of saturations, etc. Test results and data have shown that the optimum degree of saturation to the maximum shear modulus due to a capillary menisci effect was about 17~18 % at low strain amplitude and 10~15 % at intermediate strain amplitude. This paper suggests the range of threshold strain and mean shear modulus of decomposed granite soils in Suwon region. It also proposed the empirical relationship between the dynamic parameters for cement-mixed and non-mixed decomposed granite soils.