• Journal of the Korean Wood Science and Technology
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• 제13권3호
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• pp.34-40
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• 1985

The characteristics of Paulownia coreana wood used for sounding boards has been revealed through this study. The 80 specimens were selected from Paulownia coreana wood. The dynamic Young's modulus, the internal friction and resonant frequency of wood were measured by the method of making a rectangular bar resonate in the audio frequency range. The results obtained are summarized as follows: 1. The average values of the specific gravity, the dynamic Young's modulus and the internal friction concerning Paulownia coreana used for sounding boards are $0.252{\pm}0.022$, $(0.494{\pm}0.068){\times}10^{11}$ dyne/cm and $(7.89{\pm}1.692){\times}10^{-3}$ respectively. 2. The average values of resonant frequency, the velosity of sound, and K values are $504{\pm}24.298$ Hz, $5018{\pm}219.83$m/s, and $(9.907{\pm}2.05){\times}10^{-4}$ respectively. 3. The dynamic Young's modulus of Paulownia coreana increases with the increase of the specific gravity, and that on the contrary the internal friction decreases. 4. The dynamic Young's modulus was abruptly decreased as the moisture content of wood specimens was increased up to the fiber saturation point, and the internal friction was linearly increased as the moisture content of wood specimens were increased. 5. The vibration properties of Paulownia coreana are that the dynamic Young's modulus is fairly high, the internal friction is low, and the ratio of Young's modulus to specific gravity shows large value.

• Journal of the Korean Wood Science and Technology
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• 제12권4호
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• pp.3-10
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• 1984

In hot pressed wood of Pseudotsuga menziesii compressed to 0 - 50 percent at temperature 60 - $180^{\circ}C$, relative humidity conditions affecting dynamic Young's modulus of elasticity and internal friction were investigated. The results obtained are summarized as follows: Moisture absorption of the hot pressed wood decreased with increasing press temperature, but there was no effect on the amount of compression. Thickness swelling dereased with increasing press temperature, and increased with increasing amount of compression. In general, dynamic Young's modulus of elasticity showed a straight line with increasing specific gravity of specimens. Dynamic Young's modulus of elasticity decreased with increasing moisture content, but internal friction increased with increasing amount of moisture content. Dynamic Young's modulus of R specimens pressed in the radial direction showed hight values than T specimens pressed in the tangential direction.

• Journal of the Korean Wood Science and Technology
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• 제16권1호
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• pp.45-54
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• 1988

This study was carried out to investigate the fiber length, fiber width and fiber thickness on the longitudinal direction by the parts of culm and also specific gravity in air dry, dyna.mic mechanical properties and internal frictions by the internode and the node in Phyllostachys bambusoides Phyllostachys nigra var. henonis and Phllostachys edulis which were grown in Korea. The results obtained were as follows; 1. The variations of fiber length and fiber width on the longitudinal direction had a tendency to increase slightly from the butt and then to decrease toward the top. but there was not a definite variation for fiber thickness according to the parts of culm. 2. The specific gravity in air dry of internode was increased from the butt toward the top, but the specific gravity in air dry of node was not correlations with the parts of culm. 3. Dynamic Young's modulus of internode on the longitudinal direction was increased according to the heights of culms within each species, and there were in order of P. edulis P. nigra var. henonis and P. bambusoides. 4. Correation coefficients between the specific gravity and the dynamic Young's modulus were 0.837 in P. bambusoides 0.871 in P. nigra var. henonis and 0.935 in P. edulis and there was also highly significant for dynamic Young's modulus between the specific gravities in air dry. 5. There were not correlations between the internal frictions and the parts of internode.

• Journal of the Korean Wood Science and Technology
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• 제18권4호
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• pp.65-78
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• 1990

For the purpose of Improving the sounding boards for the conventional GAYAKUM, I was making approximately 202 specimens of radial board, 371 specimens of tangential board by cutting along the grain and the part of stem and 31 specimens of the disjointed traditional GAYAKUM made in Paulownia coreana. And it was conducted to measure specific gravity, dynamic Young's modulus, internal friction, resonant frequency, velosity of sound and width of annual ring by the method of the frexural vibration in a free-free bar in the audio frequency range. And it confirmed the juvenile wood by measuring wood fiber length of specimens. It was also conducted to investigate dynamic properties and moisture absorption by various heat-treatment and to test dynamic Young's modulus and internal friction for the disjointed conventional GAYAKUM. The results obtained were summarized as follow: 1. The Juvenile wood is located within about 7 annual rings from the pith in Paulownia coreana. 2. As increased with the specific gravity, the dynamic Young's modulus had more and more increased, but the internal friction had slightly decreased. 3. I think that radial board would be good for sounding board wood. because radial board is higher than tangential board in dynamic Young's mudulus and internal friction is lower than tangential board. 4. The value of mean dynamic Young's modulus on the conventional GAYAKUM, radial board and tangential board of 604 samples is $0.4283\pm0.037(\times10^{11}dyne/cm^2)$, $0.4316\pm(\times10^{11}dyne/cm^2)$ and $0.4234\pm0.112(\times10^{11}dyne/cm^2)$ respectively. The value of the radial board showed little higher than that of conventional GAYAKUM, but It had a similar tendency between conventional GAYAKUM and tangential board. 5. The annual ring width by four aspect is more narrow in north and west than that of others. 6. The values of specific gravity and dynamic Young's modulus in the mature wood showed higher than those of juvenile wood. 7. As the grain angle in the butt wood more increased to bark from pith, the dynamic Young's modulus were low. Then it was not good for sounding board. 8. It appeared that the heat-treatment for sounding board wood had a more effect to do the treatment of hotiron on surface after heat-treatment during 24 hours in $60^{\circ}C$ temperature. 9. As increased with the temperature, the rate of moisture absorption of heat-treatment wood had decreased. In conclusion, I thought that the sounding board wood for GAYAKUM would had the most effect to do the treatment of hotiron on surface after heat-treatment during 24 hours in $60^{\circ}C$ temperature using the radial board of mature wood.

• Journal of the Korean Wood Science and Technology
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• 제26권4호
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• pp.26-33
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• 1998

Acoustical properties of chestnut and paulownia woods have been determined in four film thicknesses of oriental lacquering and cashew varnishing on double surfaces of soundboard to elucidate effects of finishing. Accelerometer was attached to the specimen at one third position from one end, and specimen was hit by the impact hammer at one third position from opposite end. Data were processed by vibration analyzer. The ratio of axial-to-transverse sound velocity of untreated specimens of chestnut and paulownia were 3.25 and 5.34, respectively. Natural frequency, specific Young's modulus, acoustical coefficient, sound velocity, damping of sound radiation(DSR) and acoustical converting efficiency(ACE) decreased by oriental lacquering and cashew varnishing for both species. Damping of internal friction of chestnut decreased by oriental lacquering and cashew varnishing, but that of paulownia increased. Natural frequency. specific Young's modulus, acoustical coefficient, sound velocity, and DSR decreased with increased film thickness of both finishing materials. However, damping of internal friction and ACE showed irregular tendency with increased film thickness. Acoustical properties of cashew varnished chestnut specimen were better than those of oriental lacquered specimen. Acoustical properties of oriental lacquered paulownia specimen were better than those of cashew varnished specimen.

• 지질공학
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• 제26권4호
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• pp.593-600
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• 2016

본 연구에서는 국내의 107개 터널 설계 과정에서 수행한 현장 및 실내시험 자료 4,280개를 이용하여 암반 및 무결암의 역학적 특성을 암종 및 강도별로 분석하였다. 분석된 물리 및 역학적 특성은 단위중량, 점착력, 내부마찰각, 변형계수, 탄성계수, 포아송비, 일축압축강도, 인장강도, 투수계수, 비중이다. 평균값의 분석 결과에 의하면 편마암은 비중, 화강암은 투수계수, 퇴적암은 단위중량과 점착력, 내부마찰각, 화산암은 변형계수와 탄성계수, 일축압축강도, 인장강도, 변성암은 포아송비에서 가장 높은 값을 보인다. 역학적 특성의 분포 범위는 암종 및 강도를 고려한 분석에도 불구하고 넓게 분포하며, 이는 암반의 불균질성과 이방성에 기인하는 것으로 판단된다.

• 터널과지하공간
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• 제23권3호
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• pp.212-218
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• 2013

풍화된 응회암 시험편을 모사하기 위하여 최고 예열온도를 200, 400, 600($^{\circ}C$)로 한 예열시험편을 제작하였다. 각 예열시험편에 대한 실내시험을 통해 비중, 흡수율, 탄성파속도, 일축압축강도, 압열인장강도, 탄성계수, 포아송비, 슬레이크 내구성 지수를 측정하였다. 암석에 열을 가하는 경우 물성의 열화가 발생하는 것으로 나타났으나 예외적으로 슬레이크 내구성 지수는 별로 영향을 받지 않는 것으로 평가되었다. P-파 속도와 일축압축강도, 압열인장강도, 탄성계수, 흡수율 간에는 상당한 상관성이 있는 것으로 해석되었으며, P-파 속도를 알면 일축압축강도, 압열인장강도, 탄성계수, 흡수율을 추정할 수 있는 회귀식을 도출하였다.

• 터널과지하공간
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• 제6권1호
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• pp.1-9
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• 1996

Pocheon granite specimens were thermally treated with cycles of predetermined temperatures ranging 2$0^{\circ}C$ to $600^{\circ}C$. Characterization of thermally-induced microcracks were carried out using optical microscopy and their effect on the various physical & mechanical properties were studied. Generally. uniaxial compressive strength, Young's modulus, Poisson's ratio, elastic wave velocity and specific gravity were found to decrease with increasing temperature. From 30$0^{\circ}C$ upwards, negative lateral strains were observed, which resulted in negative Poisson's ratio. Dynamic Young's modulus and Poisson's ratio were found to be generally most sensitive indicators to thermal cracking.

• Journal of the Korean Wood Science and Technology
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• 제15권3호
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• pp.56-67
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• 1987

Plywoods used for construction as a decorative interior material are inflammable and can make fire accidents, causing destruction of human life and property. Therefore, it is indeed required to make fire-retardant treated plywood. In this study, 3.7mm yellow meranti plywoods were soaked in 18% boric acid solutions and tap water by hot-cold bath for 1/2, 2/2, 4/2, 6/2 hours and redrying of treated plywoods was carried out by press drying at the platen temperature of 110, 130, 160, $180^{\circ}C$ and then it was conducted to investigate solution absorption, drying rates, dynamic young's modulus. specific gravity and fire-retardant factors such as burning point, flame spread length. flame exhausted time, back side carbonized area and weight loss by treating time, treating solutions and platen temperature. The results are as follows; 1. When plywood was impregnated with the hot bath temperature of $70^{\circ}C$ for 1. 2, 4, 6 hours and the cold bath temperature of $15^{\circ}C$ for 2 hours respectively, retentions of boric acid were 1.565, l.597, 1.643, 1.709kg/$(30cm)^3$ and all of them exceeded the minimum retention [1.125kg/$(30cm)^3$] even in the shortest treatment. 2. In hot-cold bath method for 1/2 hours, the drying rates of treated plywood remarkably increased with the extension of platen temperature of 110, 130, 160, $180^{\circ}C$ and the values of boric acid treated plywood were 5.900, 10.196, 45.42, 54.958m.c%/min and the values of water treated plywood were 6.014, 12.373, 46.520, 55.730m.c%/min and drying rates of water treated plywood were faster than those of boric acid treated plywood. 3. The values of boric acid treated plywoods in dynamic young's modulus were widely higher than those of water treated plywoods. And it can be observed that there were highly significant differences for treating time between dynamic young's modulus, and the values of boric acid plywoods increased with the extension of treating time but on the contrary water treated plywoods were decreased values with prolonged time 4. It was observed that there were highly significant differences for platen temperature between dynamic young's modulus. When the values of water treated plywoods in dyna nic young's modulus were abruptly decreased according to the rise of platen temperature. boric acid treated plywoods showed rather increased values at $160^{\circ}C$ of platen temperature. And in 2- way interactions, there were also highly significant for dynamic young's modulus between treating time x treating solutions and platen temperature x treating solutions. 5. Correlation coefficients of fire-retardant factors were shown in table 5. It could be recognized that there were close correlations between the treating solutions and burning point, flame spread length, back side carbonized area, flame exhausted time and weight loss, but there was no correlation between fire-retardant factors and treating time and platen temperature. 6. From table 6, it can be observed that there were highly significant differences for burning point, flame spread length, flame exhausted time, back side carbonized area, weight loss between treating solutions. And in 2-way interactions, there were highly significant for burning point, flame spread length, weight loss between treating time $\times$ treating solutions.

• Imaging Science in Dentistry
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• 제37권1호
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• pp.53-59
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• 2007

Purpose : Bone mineral density (BMD) and bone microarchitecture are important determinants for bone strength. Recently micro-CT have provided possibilities for measuring a variety of structural indices to characterize bone microarchitecture. The objective of this study was to compare the BMD and micro-CT parameters with Young's modulus calculated by finite element analysis (FEA) for the evaluation of bone strength. Materials and Methods Bone specimens were obtained from the 18 female rabbits aged 16 weeks. Of those, 36 samples (right and left femur) were selected for 3D micro-CT analysis $(ANT^{TM},\;SKYSCAN,\;Belgium)$ and BMD by PIXlmus 2 (GE Lunar Co. USA). Five microstructural parameters of micro-CT, such as trabecular thickness (Tb.Th), bone specific surface (BS/BV), percent bone volume (BV/TV), structure model index (SMI) and degree of anisotropy (DOA) were studied. Young's modulus was obtained by software program (ANSYS 9.0, ANSYS Inc, Canonsburg, PA) based on micro-CT three dimensional images. Results : Young's modulus assessed by FEA correlated significantly with Tb.Th, BV/TV, BS/BV and SMI respectively. Young's modulus showed higher correlation with these rnicrostructural parameters of micro-CT than BMD. Microstructural parameters except DOA showed significant correlations within the examined group. Conclusion The microarchitectural parameters o( micro-CT and BMD represented some informations in the evaluation of bone strength assessed by FEA.