• Steel and Composite Structures
• /
• v.13 no.1
• /
• pp.15-33
• /
• 2012

For an axially loaded box-shaped member, the width-to-thickness ratio of the plate elements preferably should not be greater than 40 for Q235 steel grades in accordance with the Chinese code GB50017-2003. However, in practical engineering the plate width-to-thickness ratio is up to 120, much more than the limiting value. In this paper, a 3D nonlinear finite element model is developed that accounts for both geometrical imperfections and residual stresses and the ultimate capacity of welded built-up box columns, with larger width-to-thickness ratios of 60, 70, 80, and 100, is simulated. At the same time, the interaction buckling strength of these members is determined using the effective width method recommended in the Chinese code GB50018-2002, Eurocode 3 EN1993-1 and American standard ANSI/AISC 360-10 and the direct strength method developed in recent years. The studies show that the finite element model proposed can simulate the behavior of nonlinear buckling of axially loaded box-shaped members very well. The width-to-thickness ratio of the plate elements in welded box section columns can be enlarged up to 100 for Q235 steel grades. Good agreements are observed between the results obtained from the FEM and direct strength method. The modified direct strength method provides a better estimation of the column strength compared to the direct strength method over the full range of plate width-to-thickness ratio. The Chinese code and Eurocode 3 are overly conservative prediction of column capacity while the American standard provides a better prediction and is slightly conservative for b/t = 60. Therefore, it is suggested that the modified direct strength method should be adopted when revising the Chinese code.

• Progress in Superconductivity and Cryogenics
• /
• v.18 no.4
• /
• pp.1-4
• /
• 2016

We investigated the relation between the Cu-O bond length and the superconducting properties of $BaSnO_3$ (BSO)-added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films by using extended x-ray absorption fine structure (EXAFS) spectroscopy. 4 wt.% $BaSnO_3$ (BSO) added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films with varying thickness from $0.2{\mu}m$ to $1.0{\mu}m$ were fabricated by using pulsed laser deposition (PLD) method. The transition temperature ($T_c$) and the residual resistance ratio (RRR) of the GdBCO films increased with increasing thickness up to $0.8{\mu}m$, where the crystalline BSO has the highest peak intensity, and then decreased. This uncommon behaviors of $T_c$ and RRR are likely to be created by the addition of BSO, which may change the ordering of GdBCO atomic bonds. Analysis from the Cu K-edge EXAFS spectroscopy showed an interesting thickness dependence of ordering behavior of BSO-added GdBCO films. It is noticeable that the ordering of Cu-O bond and the transition temperature are found to show opposite behaviors in the thickness dependence. Based on these results, the growth of BSO seemingly have evident effect on the alteration of the local structure of GdBCO film.

• Journal of the Korean Society of Physical Medicine
• /
• v.18 no.3
• /
• pp.31-37
• /
• 2023

PURPOSE: This study aimed to investigate the relationship between being underweight and respiratory function indicators such as pulmonary function, respiratory muscle strength, and diaphragm thickness in normal adults without lung disease. METHODS: The participants in this experiment were thirty young adults. To compare the respiratory function between the underweight and normal weight individuals, 15 participants were selected from each of the underweight and normal weight groups based on body mass index. Respiratory function tests were conducted through pulmonary function tests and respiratory muscle strength tests. Diaphragm thickness was measure with ultrasonography, and physical characteristics were obtained from grip strength and waist circumference. An independent t-test was used to compare the averages of the parameters measured in the two groups. RESULTS: In the respiratory function tests between the two groups, statistically significant differences (p < .05) emerged in the ratio of the predicted forced vital capacity (%FVC), the ratio of the predicted forced expiratory volume in one second (%FEV1), maximal expiratory pressure (MEP), and diaphragm thickness at the functional residual capacity (FRC). There was no statistically significant difference in the forced vital capacity, forced expiratory volume in one second, maximal inspiratory pressure, diaphragm thickness at the total lung capacity, and thickening ratio (p > .05). CONCLUSION: Decreases in some variables of respiratory function, such as the %FVC, %FEV1, MEP, and diaphragm thickness at the FRC were observed in underweight subjects. However, it is difficult to determine whether it affected the overall respiratory function. Future studies are needed to clearly identify the relationship between being underweight and respiratory function.

• Journal of the Korean Society for Precision Engineering
• /
• v.9 no.1
• /
• pp.66-74
• /
• 1992

The joining processes of aluminum alloy tubes and polyurethane cores by electromagnetic impulsive compression are studied. The influences of various geometrical factors (the length of joined part, the thickness of tube, and the clearance between tube and core) and the process factors(the discharged energy and the number of discharge)are examined experimentally and discussed. And the magnetic pressure in metal/polymer joining is calculated and is compared to the pressure in metal/metal joining. The following results are obtained: (1) The joining strength is dependent upon the residual radial strain of the polyurethane cores. (2) The joining strength increases as discharged energy and the number of discharge increase, but decreases as the clearance, thickness and joining length of tube increases. (3) In the case of metal/polymer joining energy loss is increased and the value of magnetic pressure is less than that in the case of metal/metal joining.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2003.10a
• /
• pp.91-94
• /
• 2003

Laminated composites are liable to fatal damage under impact load due to the fact that they have no reinforcement in the thickness direction. To overcome the inherent weakness, three dimensional (3D) textile reinforcements have drawn much interests. In this paper, impact performance of 2D and 3D textile composites has been characterized. For 2D composites, fiber bundle size and fiber pattern have been varied. For 3D composites, orthogonal woven preforms of different density and type of through-thickness fibers have been studied. To assess the damage after the impact loading, specimens were subjected to C-scan nondestuctive inspection. Compression after impact (CAI) were also conducted in order to evaluate residual compressive strength.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.08a
• /
• pp.19-24
• /
• 2004

Symmetrical and asymmetrical rolling was performed in AA 1050 sheets. Asymmetrical rolling was carried out by using different roll velocities of upper and lower rolls. The effect of the reduction per rolling pass on the formation of textures and microstructures during symmetrical and asymmetrical rolling was studied. In order to intensify the shear deformation, symmetrical and asymmetrical rolling was carried out without lubrication. The strain states associated with rolling were investigated by simulations with the finite element method (FEM). A fairly homogeneous residual shear strain throughout the sheet thickness was observed after asymmetrical rolling. Symmetrical rolling with a high friction gave rise to a strong net shear strain gradient in the sheet thickness.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.7 no.2
• /
• pp.209-218
• /
• 2003

The analytical studies included nonlinear finite element analysis of split-tee connection details subjected to axial load and lateral load. A three-dimensional model of the connections between CFT columns and H-beams has been developed. Both initial geometrical imperfections and residual stresses are taken into consideration. A geometrically nonlinear load-displacement analysis of the structure containing the imperfection is then performed, using the Riks method. Analytical results are compared with existing experimental results. Extensive parametric analyses are carried out to investigate the relation of the connections between CFT columns and H-beam to various parameters such as the axial load, column width-thickness ratio, and split-tee thickness.

• Journal of Powder Materials
• /
• v.17 no.3
• /
• pp.197-202
• /
• 2010

Low temperature degradation behavior in yttria stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics was microscopically observed from the phase contrast between monoclinic surface and tetragonal matrix. The degradation behavior was dependent on the surface treatment of sintered Y-TZP, even if the sintering history is same. In the mirror polished specimen, the monoclinic layer appeared in a uniform thickness from the surface. On the contrary, for the specimen with coarse scratch, the thickness of degraded surface was more than double especially from the coarse scratch. Since the scratch results in local deformation, the residual stress should be induced around the scratch. With the transformation from tetragonal to monoclinic, the volume expansion exerts a stress on a neighboring grains and promotes a successive phase transformation. Such a autocatalytic effect can be triggered from the part of coarse scratch.

• Journal of the Korean Institute of Gas
• /
• v.22 no.5
• /
• pp.62-71
• /
• 2018

According to own investigation conducted by Korea Gas Safety Corporation Gas Safety Research Institute in 2017, the length of underground pipes in domestic high-pressure gas pipelines is approximately 770km, of which 84% is buried in Ulsan and Yeosu industrial complexes. In particular, 56% of underground pipelines have been in operation for more than 20 years. This suggests urgent management of buried high pressure gas pipelines. PHMSA in US and EGIG in Europe, major causes of accidents in buried gas pipelines are reported as third party damage, external corrosion and loss of pipe wall thickness. Therefore, it is important to evaluate whether the defects affect the remaining life of the pipe when defects occur in the pipe. DNV and ASME have evaluated the residual strength of pipelines through the hydraulic rupture test using pipe specimens with artifact flaws. Once the operating pressure is known through the residual strength of the pipe, the wall thickness at the point at which the pipe ruptures is calculated. If we know the accurate rate of corrosion growth, we can predict the remaining life of pipe. In the study, we carried out experiments with A53 Grade.B and A106 Grade.B, which account for 80% of domestic buried pipes. In order to modify the existing model equation, specimens with a defect depth of 80% to 90% was tested, and a formula expressing the relationship between defect and residual strength was made.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.3
• /
• pp.387-395
• /
• 2013

Recently, several circumferential cracks were found in the control rod drive mechanism (CRDM) nozzles of U.S. nuclear power plants. According to the accident analyses, coolant leaks were caused by primary water stress corrosion cracking (PWSCC). The tensile residual stresses caused by welding, corrosion sensitive materials, and boric acid solution cause PWSCC. Therefore, an exact estimation of the residual stress is important for reliable operation. In this study, finite element simulations were conducted to investigate the effects of the tube geometry (thickness and radius) on the residual stresses in a J-groove weld for different CRDM tube locations. Two different tube locations were considered (center-hole and steepest side hill tube), and the tube radius and thickness variables ($r_o/t$=2, 3, 4) included two different reference values ($r_o$=51.6, t=16.9mm).