• Progress in Superconductivity and Cryogenics
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• v.6 no.1
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• pp.6-11
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• 2004

The influences of mixed strain mode of bending-tension on the critical current. Ic in externally reinforced Bi-2223 tapes and their interaction were investigated in this study. A test fixture which providing a mixed deformation mode of bending-tension to HTS tapes has been newly devised. When the total strain induced in the tape in the mixed strain mode was expressed by the superposition of the bending and tensile strains the irreversible strain for the critical current degradation of Bi-2223 tapes increased, as compared with the simple bending mode case. The $I_c$ degradation at the region exceeding the irreversible strain showed a medium between the simple bending case and the simple tension case. As the initial bending strain imparted increased , namely as the diameter of mandrel adopted decreased. the apparent irreversible strain in Bi-2223 tapes increased . but the increment became smaller As a result. it can be found that the tension to be applied to bent Bi-2223 tapes during cabling should be smaller. as the mandrel diameter becomes smaller.

• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.2
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• pp.36-43
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• 2010

In this study, the buckling loads and mode shapes characteristic of circular and non-circular(elliptical) closed composite shells were analyzed. To analyses the buckling behaviors, we develop and report an improved generalized shell element called 4EAS-FS through a combination of enhanced assumed strain and the substitute shear strain fields. A flat shell element has been developed by combining membrane element with drilling degree-of-freedom and a plate bending element. The combined influences of length, thicknesses, cross-sectional parameters, and fiber-angle on the critical buckling loads and mode shapes of circular and non-circular(elliptical) closed shells are examined.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.713-721
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• 2012

The finite element simulations of fatigue crack growth are carried out. Using only the mechanical properties usually obtained from the tensile test as input data, we attempted to predict the fatigue crack growth behavior. The critical crack opening displacement is determined by monitoring the change in displacements at the node close to the crack tip. Crack growth is simulated by debonding the crack tip node. The exponent in the Paris law was determined and compared to the published exponent. Plotting with respect to the effective stress intensity factor range yielded more consistent results.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.134-138
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• 2003

The influences of mixed mode of bending-tension on the Ic degradation and their interaction on the strain effect were evaluated in this study. A test fixture which applies a mixed deformation mode of bending-tension to HTS tapes has been newly devised. When the strain induced in the tape due to the mixed deformation mode was expressed as a total tensile strain, the irreversible strain to the critical current degradation of Bi-2223 tapes increased when compared with the case of simple bending mode, and the value at both ends were larger than that at the central region of the bend part. The Ic degradation behavior at the region exceeding the irreversible strain showed quiet a rapid drop of the Ic when compared with the simple bending cases. As the applied bending strain increased namely as the diameter of mandrel adopted decreased, the apparent irreversible strain of Bi-2223 tapes increased However, the increment decreased as the mandrel diameter decreased. As a result, it could be found that the tension to be applied to the Bi-2223 tapes during cabling of HTS tapes should be smaller, as the mandrel diameter becomes smaller.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.457-464
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• 2006

Fiber-reinforced composite materials due to their high specific strength, high stiffness and light weight are becoming increasingly used in many engineering industry, especially in the aerospace, marin and civil, etc. In this paper, the buckling load and mode shapes of composite laminates with elliptical cross-section including transverse shear deformations are analyzed. For solving this problems, a versatile flat shell element has been developed by combining a membrane element with drilling degree-of-freedom and a plate bending element. Also, an improved shell element has been established by the combined use of the addition of enhanced assumed strain and the substitute shear strain fields. The combined influence of shell geometry and elliptical cross-sectional parameter, fiber angle, and lay-up on the buckling loads of elliptical cylinder is examined. The critical buckling loads and mode shapes analyzed here may serve as a benchmark for future investigations.

• Magazine of the Korea Concrete Institute
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• v.3 no.4
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• pp.79-88
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• 1991

In this study, fracture tests were carried out in order to investigate the fracture behavior of SFRC(Steel Fiber Peinforced Concrete) with initial cracks. The relationships between loading. strain, mld-span deflections and CMOD(Crack Mouth Opening Displacement) of the beams were observed under the three point loading system. The effect of the fiber content and the initial crack ratio on the concrete fracture behavior were studied and the fracture toughness, the critical energy release ratio and the fracture energy were also calcul ated from the test results. From the test results, it was known that when the fiber contents are between 0.5% and 1.0%, and 1.5% the average fracture energy of SFRC specimens is about 7~10 times. and about 15 times better than that of the plam concrete specimens respectively.ively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.191-203
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• 2006

The vibration characteristics of composite stiffened laminated plates with stiffener is presented using the assumed natural strain 9-node shell element. To compare with previous research, the stiffened plates are composed of carbon-epoxy composite laminate with a symmetric stacking sequence. Also, the result of the present shell model for the stiffener made of composite material is compared with that of the beam model. In the case of torsionally weak stiffener, a local buckling occurs in the stiffener. In this case, the stiffener should be idealized by using the shell elements. The current investigation concentrates upon the vibration analysis of rectangular stiffened and unstiffened composite plates when subjected to the in-plane compression and shear loads. The in-plane compression affect the natural frequencies and mode shapes of the stiffened laminated composite plates and the increase in magnitude of the in-plane compressive load reduces the natural frequencies, which will become zero when the in-plane load is equal to the critical buckling load of the plate. The natural frequencies of composite stiffened plates with shear loads exhibit the higher values than the case of without shear loads. Also, the intersection, between the curves of frequencies against in-plane loads, interchanges the sequence of some of the mode shapes as a result of the increase in the inplane compressive load. The results are compared with those available in the literature and this result shows that the present shell model for the stiffened plate gives more accurate results. Therefore, the magnitude, direction type of the in-plane shear and compressive loads in laminated composite stiffened plates should be selected properly to control the specific frequency and mode shape. The Lanczos method is employed to solve the eigenvalue problems.

• Journal of the Korean Geotechnical Society
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• v.29 no.10
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• pp.57-66
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• 2013

Societal interest on a faster transportation demands an increase of the train speed exceeding current operation speed of 350 km/h. To trace the pattern of variations in displacements and subsoil stresses in the concrete slab track system, finite element simulations were conducted. For a simple track-vehicle modeling, a mass-point system representing the moving train load was developed. Dynamic responses with various train speeds from 100 to 700 km/h were investigated. As train speeds increase the displacement at rail and subsoil increases nonlinearly, whereas significant dynamic amplification at the critical velocity has not been found. At low train speed, the velocity of elastic wave carrying elastic energy is faster than the train speed. At high train speed exceeding 400 km/h, however, the train speed is approximately identical to the elastic wave velocity. Nonlinearity in the stress history in subsoil is amplified with increasing train speeds, which may cause significant plastic strains in path-dependent subsoil materials.

• The Journal of Engineering Geology
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• v.27 no.1
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• pp.31-40
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• 2017

The slope stability analysis by the limit equilibrium method has the disadvantage that it can be applied only when the analysis is performed by setting the critical plane after analyzing the active surface many times and the soil is uniform and only the safety factor can be calculated. However, the analysis using the strength reduction analysis method has advantages that the engineer can judge various aspects and calculate the safety factor. In this study, the safety factor according to the change of slope and shear strength was compared and analyzed using limit equilibrium analysis and strength reduction method. It is suggested that it is desirable to use the strength reduction method which can synthetically review the stress, displacement, and strain in the soil.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.121-127
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• 2014

An atomistic-based finite bond element model for predicting the tearing mode (mode III) fracture of a single-layer graphene sheet (SLGS) is developed. The model uses the modified Morse potential for predicting the maximum strain relationship of graphene sheets. The mode III fracture of graphene under out-of-plane shear loading is investigated with extensive molecular mechanics simulations. Molecular mechanics is used for describing the displacements of atoms in the area near a crack tip, and linear elastic fracture mechanics is used outside this area. This work shows that the molecular mechanics method can provide a reliable and yet simple method for determining not only the shear properties of SLGS but also its mode III fracture toughness in the armchair and the zigzag directions; the determined mode III fracture toughness values of SLGS are $0.86MPa{\sqrt{m}}$ and $0.93MPa{\sqrt{m}}$, respectively.