• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.5 s.248
• /
• pp.505-511
• /
• 2006

In the present paper, approximate plastic limit load solutions fur pipe bends under combined internal pressure and bending are obtained from detailed three-dimensional (3-D) FE limit analyses based on elastic-perfectly plastic materials with the small geometry change option. The present FE results show that existing limit load solutions for pipe bends are lower bounds but can be very different from the present FE results in some cases, particularly for bending. Accordingly closed-form approximations are proposed for pipe bends under combined pressure and in-plane bending based on the present FE results. The proposed limit load solutions would be a basis of defective pipe bends and be useful to estimate non-linear fracture mechanics parameters based on the reference stress approach.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.05a
• /
• pp.401-402
• /
• 2006

In the present paper, approximate plastic limit load solutions for pipe bends under combined internal pressure and bending are obtained from detailed three-dimensional (3-D) FE limit analyses based on elastic-perfectly plastic materials with the small geometry change option. The present FE results show that existing limit load solutions for pipe bends are lower bounds but can be very different from the present FE results in some cases, particularly for bending. Accordingly closed-form approximations are proposed for pipe bends under combined pressure and in-plane bending based on the present FE results. The proposed limit load solutions would be a basis of defective pipe bends and be useful to estimate non-linear fracture mechanics parameters based on the reference stress approach.

• Journal of Power System Engineering
• /
• v.11 no.1
• /
• pp.92-97
• /
• 2007

It is important to compute the structural analysis of plate structures in structural design. In this paper, the author uses the finite element-transfer stiffness coefficient method (FE-TSCM) for the structural analysis of plate structures. The FE-TSCM is based on the concept of the successive transmission of the transfer stiffness coefficient method and the modeling technique of the finite element method (FEM). The algorithm for in-plane structural analysis of a rectangular plate structure is formulated by using the FE-TSCM. In order to confirm the validity of the FE-TSCM for structural analysis of plate structures, two numerical examples for the in-plane structural analysis of a plate with triangular elements and the bending structural analysis of a plate with rectangular elements are computed. The results of the FE-TSCM are compared with those of the FEM on a personal computer.

• Journal of the Korean Magnetics Society
• /
• v.16 no.1
• /
• pp.45-50
• /
• 2006

Oxygen-deficient anatase and rutile titanium dioxide $(TiO_{2-\delta})$ thin films were prepared by a sol-gel method and their structural, electronic, and magnetic properties were investigated. Both anatase and rutile $TiO_{2-\delta}:Fe$ Fe films exhibited ferromagnetism at room temperature for a limited range of Fe doping. For the same amount of Fe doping, the anatase sample exhibited a higher magnetic moment than the rutile one. Result of conversion electron Mossbauer spectroscopy measurements indicates that $Fe^{3+}$ ions substituting the octahedral $Ti^{4+}$ sites mainly contribute to the room-temperature ferromagnetism. Some of the anatase $TiO_{2-\delta}:Fe$ films exhibited p-type character but the observed feromagnetism turns out to be independent of the hole concentration. The room-temperature ferromagnetism can be explained in terms of a direct ferromagnetic coupling between two neighboring $Fe^{3+}$ ions via an electron trapped in oxygen vacancy in $TiO_{2-\delta}:Fe$.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.16 no.3
• /
• pp.23-33
• /
• 2012

Dynamic response measurements from natural excitation were carried out for three 18-story office buildings to determine their inherent properties. The beam-column frame system was adopted as a typical structural form, but a core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. To extract modal parameters such as natural frequencies, mode shapes and damping ratios from a series of vibration records at each floor, the most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were applied. Extracted frequencies and mode shapes from the different identification methods showed a greater consistency for three buildings, however the three lower frequencies extracted were 1.2 to 1.7 times as stiff as those obtained using the initial FE models. Comparing the extracted fundamental periods with those estimated from the code equations and FE analysis, the FE analysis results showed the most flexible behavior, and the most simple equation that considers the building height as the only parameter correlated fairly well with test results. It is recognized that such a discrepancy arises from the fact that the present tests exclude the stiffness decreasing factors like concrete cracking, while the FE models ignore the stiffness increasing factors, such as the contribution of non-structural elements and the actual material properties used.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.11 s.254
• /
• pp.1425-1432
• /
• 2006

Coating layers on a coated sheet steel frequently affect distributions of strain rate of sheets and deteriorate the frictional characteristics between sheets and tools in sheet metal forming. Thus, it is important to identify the deformation behavior of these coatings to ensure the success of the sheet forming operation. In this study, the technique using nano-indentation test, FE-simulation and Artificial Neural Network(ANN) were proposed to determine the power law stress-strain behavior of coating layer and the power law behavior of extracted coating layers was examined using FE-simulation of drawing and nano-indentation process. Also, deep drawing test was performed to estimate the formability and frictional characteristic of coated sheet, which was calculated using the linear relationship between drawing force and blank holding force obtained from the deep drawing test. FE-simulations of the drawing process were respectively carried out for single-behavior FE-model having one stress-strain behavior and for layer-behavior FE-model which consist of coating and substrate separately. The results of simulations showed that layer-behavior model can predict drawing forces with more accuracy in comparison with single-behavior model. Also, mean friction coefficients used in FE-simulation signify the value that can occur maximum drawing force in a drawing test.

• Proceedings of the Korean Magnestics Society Conference
• /
• 1994.10a
• /
• pp.26-27
• /
• 1994

• Proceedings of the KWS Conference
• /
• 1998.05a
• /
• pp.121-124
• /
• 1998

• Proceedings of the Korean Magnestics Society Conference
• /
• 1995.05a
• /
• pp.32-33
• /
• 1995

• Aerospace Engineering and Technology
• /
• v.11 no.1
• /
• pp.91-97
• /
• 2012

The structural analyses and experimental results for the bellows of a gas-generator liquid oxygen shut-off valve were presented. The bellows experiences axial compression and external high pressure loadings at cryogenic temperatures. The analyses were performed using EJMA (Expansion Joint Manufacturing Association) standard and the commercial FE (finite element) analysis program, Abaqus v6.9, at room and cryogenic temperatures. The spring modulus, the induced stress and the expected fatigue life of the bellows were compared respectively. The effects by the contact and the material plasticity on the FE analysis results were also analyzed. Also, FE analyses related to a burst test were presented.