• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.502-509
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• 2001

In this paper, when stress waves are propagated along the reinforced direction of the composite, the characteristic equation of Rayleigh wave is derived. The relationships between velocities of stress waves and Rayleigh wave are studied for anisotropic ratios(E(sub)11/E(sub)12 or E(sub)22/E(sub)11). The increments of anisotropic ratios is made by using known material properties and being constant of basic properties. When the anisotropic ratios are increased, Rayleigh wave velocities to the shear wave velocities are almost equal to 1 with any anisotropic ratios. Rayleigh wave velocities to the longitudinal wave velocities and Shear wave velocities ratio to the longitudinal wave velocities are almost identical each other, they are between 0.12 and 0.21. When the anisotropic ration is very high, that is, E(sub)11/E(sub)22=46.88, Rayleigh wave velocities and the shear wave velocities are almost constant with Poissons ratio, longitudinal wave velocities are very slowly increased with the increments of Poissons ratios. When E(sub)11(elastic modulus of the reinforced direction)and ν(sub)12 are constant, Rayleigh wave velocities and the shear wave velocities are steeply decreased with the increments of anisotropic ratios and the velocities of longitudinal wave are almost constant with them. When E(sub)22(elastic modulus of the normal direction to the fiber) and ν(sub)12 are constant, Rayeigh wave velocities is slowly increased with the increments of anisotropic ratios, the shear wave velocities are almost constant with them, the longitudinal wave velocities are steeply increased with them.

• Proceedings of the Korean Geotechical Society Conference
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• 1997.10a
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• pp.261-266
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• 1997

• The Journal of Engineering Geology
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• v.6 no.2
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• pp.103-110
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• 1996

This study shows the variation of poisson's ratio according to stress for the Cretaceous sandstones and shale in the Euiseoung Subbasin. To make a mechanical experiment, samples prepared with 3.0 cm in diameter and 6.2 cm in length were used in testing stress and strain. Generally poisson's ratio has been considered as one of properties, but contrary to steel, the test result makes sure that poisson's ratio has functional relation to stress. I had used four methods to calculate poisson's ratio, Poisson's ratio shows considerable different results according to the calculating, method but it has similar tendency in an elastic limit. Poisson' s ratio increases rapidly and is distinguished clearly in internal fracture region according to the calculating method. Poisson's ratio of sandstone and shale is different from one another in low and high stress regimes,but it is linearly proportional to the stress in an elastic regimes, that is, ${\nu}_t={\;}{\nu}_0+P_{\sigma}({\nu}_0$:first stage Poisson's ratio, ${\nu}_t$:poisson's ratio, P: poisson's coefficient, $\sigma$:stress). Poisson's ratios of two kinds of rock samples show continuous variation from 0.1 to 0.21 in an elastic regime. The variation of poisson's ratio is much wider in an internal fracture regine. It varies from 0.22 to 0.45 in sandstone, which is out of elastic regime.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.149-159
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• 2013

This paper deals with behaviors of Poisson's ratio with water content through uniaxial compressive strength against 307 individual rock cores, which are classified into sedimentary, igneous and metamorphic rock. Poissons' ratio demonstrates independent behaviors and does not correlate with mechanical and physical parameter of rocks. The water content behavior of Poissson's ratio represents decrease, increase and random style. Rock samples with decreasing behavior demonstrate absolute preponderance above the 70% level. As Poisson' ratio shows independent behaviors, it should be considered based on experimental results of in-situ rock in the process of design, construction, and supervision.

• Journal of Aerospace System Engineering
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• v.4 no.2
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• pp.1-9
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• 2010

An airless tire has advantages over the conventional pneumatic tire in terms of flat proof and maintenance free. According to the recently disclosed inventions on the airless tire, non-pneumatic tire (NPT) consists of the flexible polygon spokes. Considering the NPT structure, the spokes undergo the tension-compression cyclic loading while the tire rolls. Therefore the spokes of NPT are required to have both stiffness and resilience under the cyclic tensile-compressible loading. In general, if a material has a high stiffness, it shows a low elastic strain limit. In this paper, using the auxetic honeycomb structure with negative poissons's ratio, the spokes of NPT tire are designed to have both stiffness and resilience. Finite element based numerical simulation of the contact pressure of a NPT is carried out with ABAQUS.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.57-62
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• 2003

Nano-bending method is presented to measure the Poisson's ratio of thinfilms for MEMS (Micro-Electro-Mechanical Systems) applicaiton. The douvle-ring specimen is designed and fabricated based on the surface micromachining process to facilitate the measurement of the Poisson's ratio. The Poisson's ratio can be obtained through analyzing the linear load-displacement relationship of the double ring specimen subjected to nano-indenter loading. The Present nano-bending mehod is an in-situ measurement approach due to the compatibility to the surface micromachining process. The Poisson's ratio is locally obtained at the location of the double ring specimen with micro dimension. To validate the nano-bending method, the Poisson's ratio of LPCVD (Low Pressure Chemical Vapor Deposition) poly-silicon with thickness of 2.3㎛ is investigated. Experimental results reveal that the Poisson's ratio of the poly-silicon film is 0.2569. The standard deviation of the nano-bending measurement for the stiffness of double ring specimens is 2.66%.

• Asian-Australasian Journal of Animal Sciences
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• v.3 no.3
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• pp.231-242
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• 1990

A study is reported which investigated the additive nature of digestible energy (DE) from dietary nutrients and to estimate the relative energy values of different energy-yielding nutrients in practical trout diets. A growth study was conducted over 12 weeks with 6 diets. Rainbow trout (Oncorhynchus mykiss) were fed diets once a day ad libitum. Digestible energy values determined and calculated had direct relationship indicating additive nature of such values for feed ingredients. Overall growth performance was best in a diet containing 33% digestible protein (DP) with a DP/DE ratio of 18.6. A reduction in digestible protein level with the same DP/DE rat io led to a significant decrease in growth and feed efficiency. The increase of 7% of lipid with concomitant decrease in protein resulted in the relative gain of 130% in growth and nutrient retention, suggesting that 1 g of lipid is equal to about 1.3 g of proteins in terms of net energetic value. Replacement of 10% of dietary lipid by carbohydrates led to a slight decrease in energy retention efficiency but to a great increase in lipid retention efficiency (130%) showing that dietary carbohydrates led to increased lipogenesis.

• Tunnel and Underground Space
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• v.24 no.4
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• pp.325-333
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• 2014

Hydraulic fracturing is the key technology for production of shale gas, which is one of the major unconventional resources. Brittleness index is one of the most important mechanical properties which determine the efficiency of hydraulic fracturing. It was required that the production of shale gas increases with more brittle behavior. Confusingly, there are numerous definitions available for brittleness of rock. This paper summarizes various definitions of brittleness index, and presents correlation analysis of the brittleness indices by using the laboratory experimental results of 48 shale specimens in Korea. Generally, it shows a very weak positive correlation between the brittleness index ($B_1$) which is the ratio of uniaxial compressive strength to tensile strength and the brittleness index ($B_3$) which is calculated by using the Youngs modulus and Poisson's ratio. In addition, the role of Poissons ratio is not clear in defining brittleness indices. In conclusion, standardization of definition for brittleness index is required to apply it to hydraulic fracturing as a parameter for predicting the efficiency.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.73-80
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• 1997

This paper describes structural optimization of optical fiber-wound mandrel hydrophones with Finite Element Method (FEM). The hydrophone is supposed to have operation frequency range of up to 10 kHz and show omni-directional sensitivity pattern at 5 kHz. Studied parameters are mandrel geometry, molding thickness, and material properties of constitutional parts of the hydrophone. Theoretical calculation result shows that pressure sensitivity of the hydrophone increased as either mandrel length or molding thickness gets larger. Also higher pressure sensitivity requires a mandrel or molding material with relatively low Youngs modulus or Poissons ratio. Hydrophone bandwidth increases either as the mandrel length becomes shorter or as the mandrel becomes harder. The omni-directional characteristic is improved as the mandrel length becomes shorter, at 5 kHz. With the above results, we determine the structure of an optical fiber-wound mandrel hydrophone which has the pressure sensitivity of $30 {\times} 10_{-7}$ Rad./Pa, operation frequency range of up to 10 kHz, and shows omni-directional sensitivity pattern at 5 kHz.