• Journal of the Korean Institute of Gas
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• v.15 no.5
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• pp.37-41
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• 2011

This paper presents the strength safety of a hydrogen gas composite fuel tank, which is analyzed using a FEM based on the criterion of US DOT-CFFC and Korean Standard. A hydrogen gas composite tank in which is fabricated by an aluminum liner of 6061-T6 material and carbon fiber wound composite layers of T800-24K is charged with a filling pressure of 70MPa and a gas storage capacity of 130 liter. The FEM results indicated that von Mises stress, 255.2MPa of an aluminum liner inner tank is low compared with that of 95% yield strength, 272MPa. And a carbon fiber stress ratio of a composite fuel tank is 3.11 in hoop direction and 3.04 in helical direction. These data indicate that a carbon fiber gas tank is safe in comparison to that of a recommended criterion of 2.4 stress ratio. Thus, the proposed composite tank with 130 liter capacity and 70MPa filling pressure is usable in strength safety.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1990-2001
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• 1991

The fatigue life and crack penetration behavior of high strength steel have been studied in detail both experimentally and analytically. The fatigue crack shape of a smooth specimen is almost semicircular, while a specimen with stress concentration becomes semielliptical according to stress concentration shape. The aspect ratio of smooth specimens calculated using the Newman-Raju's formular is smaller than the value obtained from the experiment. On the other hand, the aspect ratio of the stress concentration specimen shows a good agreement with experimental results. It is found that the crack growth behavior on the back surface after the penetration is unique and can be divided into three stages ; rapid growth region, constant growth region and acceleration growth region. By using the K value suggested in this study, the particular crack growth behavior and crack shape can be estimated quantitatively.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.653-658
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• 1997

Recently, carbon Fiber sheet (CFS) is frequently used for strengthening deteriorated concrete structures. To strengthening damaged structures, the property and characteristic of the bond between CFS and the concrete surface must be understood. The tensile test of single lap shear specimen was performed to study bond strength, bond stress distribution and stress transfer between CFS and concrete surface according to the bond length. Based on the test results, there were ultimate influence length (UIL) in which bond stress was distributed, and ultimate strain reduction ratio (USRR) by which strain was reduced linearly. Bond resisting force (BRF) was estimated by UIL and USRR, and which was compared with ultimate loads. According to the results of comparison, it was shown that ultimate bond strength could be estimated reasonablely by BRF.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.501-506
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• 1998

This paper is an experimental study on the flexural strength and ductility capacity of reinforced high performance concrete beams with the concrete which has compressive strength of 600~700kg/$\textrm{cm}^2$, slump value of 20~25cm and slump-flow value of 60~70cm. Total 8 beams with different tensile reinforcement ratio and pattern of loading were tested. Form the results of reinforced high performance concrete beams, the equivalent stress block parameters proposed by MacGregor et al. or New Zealand code are recommended to use. Also, an extreme fiber concrete compressive strain of reinforced high performance concrete beams are distributed 0.0033~0.0048. In reinforced high performance concrete beams, reinforcement ratio in order to insure curvature ductility index 2 and 4 propose by ACI code should be less than those of reinforced normal strength concrete beams.

• Journal of Korea Foundry Society
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• v.9 no.3
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• pp.237-246
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• 1989

This study has been carried out to investigate the difference of rolling life and rolling wear characteristics for various high strength ductile iron castings under unlubricative dry rolling condition by Amsler type wear test with 9.09% sliding ratio. The tensile strength of the castings have been obtained 80, 90 and $100kg.f/mm^2$ as cast-state with pearlitic, bainitic and martensitic matrix structures alloyed with Mo, Cu and Ni. It has been found that the amount of rolling wear is decreased when the tensile strength and hardnees of the castings are increased. The amount of rolling wear is increased, when the maximum compressive stress are increased. The maximum weight loss ratio of rolling wear of the castings are same at the 70000 numbers of revolution with out the maximum compressive stress.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.63-66
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• 2000

Stress variation due to size variation and the eccentricity of ring type tensile specimen was analyzed by FLAC program. To get the stable tensile strength the ratio of inner to outer ring diameter should be within a certain range. Diameter ratio of 0.3 was suggested to be adequate. It seemed to be difficult to determine the tensile strength because of stress distortion if eccentricity exceeded home limit. To limit the error in 10%, lateral and axial eccentricity was analyzed to be in the limits of 3% and 10%, respectively.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.316-319
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• 2000

Stress variation due to size variation and the eccentricity of ring type tensile specimen was analyzed by FLAC program. To get the stable tensile strength the ratio of inner to outer ring diameter should be within a certain range. Diameter ratio of 0.3 was suggested to be adequate. It seemed to be difficult to determine the tensile strength because of stress distortion if eccentricity exceeded some limit. To limit the error in 10%, lateral and axial eccentricity was analyzed to be in the limits of 3% and 10%, respectively.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.5
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• pp.45-54
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• 2014

This study was performed to evaluate compressive strength, flexural strength, static modulus of elasticity, stress-strain ratio and durability of abrasion on EVA concrete reinforced steel fiber (SF) in order to use hydraulic structures, underground utilities, offshore structures and structures being applied soil contaminated area. It is used ordinary portland cement, crushed coarse aggregate, nature fine aggregate, EVA redispersible polymer powder, superplasticizer and deforming agent to find optimum mix design of EVA concrete reinforced steel fiber. EVA concrete reinforced SF was effected on the improvement of mechanical properties and durability of abrasion.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.7-14
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• 2003

In this study, undrained shear test was performed$K_o$ consolidation in order to study the shear strength characteristics of oysters-marine clay mixtures for three mixed ratios(0%, 25% and 50%). And, in order to study shear strength characteristics of oysters-marine clay mixtures, three different effective vertical stresses(200, 300 and 400kPa) were applied for the $K_o$ consolidation tests. In addition three different axial strain rates(0.005%/min, 0.05%/min, 0.5%/min) were applied for the case of effective vertical stress, 300kPa. According to experimental results, the more mixed ratios were increased, the more deviator stress was increased by crushing effect of oysters particles. especially, when effective vertical stress is 300kPa and mixed ratio increase from 25% to 50%, Test shows the increase of shear strength. But axial strain rate was not effect on the undrained shear strength. In the comparison and analysis that are based on the values of tests on the oysters-marine clay mixtures and the Mayne & Bishop's empiric formula, the undrained shear strength ratio shows a similar pattern of the tests. But for the prediction of the coefficient of the pore water pressure, the value of empiric formula shows more overestimated than the values of the tests at 0%, mixture ratio.

• Journal of Korean Society of Steel Construction
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• v.13 no.2
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• pp.123-131
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• 2001

The objective of this study is to investigate the criteria of the width-to-thickness ratio and to evaluate the buckling strength of high strength steel beam-columns and to compare their buckling strength with design codes, which are the Limit State Design code and the Allowable Stress Desogn code(drift). SM520TMC and SM570Q class steels are used for high strength steels. The coupon test and the stub column test were carried out to investigate the properties of high strength steels and the stress-strain curves of stub columns. The buckling strength of high strength steel beam-columns are assessed by numerical analysis used axial force, moment and curvature relationships.