• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.413-416
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• 2007

In general, by means of the electrodepositing technique, a copper foil sample was prepared with a high purity and a high density. But the mechanical properties of the electrodepositing copper foil was lower than it's the rolling copper foil. However, the production of copper foil with approximately 36 microns thick in rolling process was very difficult. This paper describes the outline of the high accuracy cold rolling in 6 high mill which was developed for the purpose of rolling very thin accurate gauge copper foil(36 micron thick), and give several rolling characteristic of 600 mm wide copper foil. a) Large strain can be accumulated pass by pass in industrial multi-pass rolling processing to overcome large critical strain for thickness accuracy through optimization of rolling schedule. b) Also, permissible tension for rolling 0.45 $\sim$ 0.036 mm thick copper strip stably in accordance with the each pass work had been established by FEM simulation results. c) During the plate rolling process, considerable values of the forces of material pressure on the tool occur. These pressures cause the elastic deformation of the roll, thus changing the shape of the deformation region. A numerical simulation of roll deflection during cold rolling is presented in the paper. d) The proposed pass schedule can roll very thin copper foil of 36 micron thickness to a tolerance of ${\pm}1$ microns. The validity of simulated results was verified into rolling experiments on the copper foil.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.629-635
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• 2010

An SGBEM (symmetric Galerkin boundary element method)-FEM alternating method has been proposed by Nikishkov, Park and Atluri. This method can be used to obtain mixed-mode stress intensity factors for planar and nonplanar three-dimensional cracks having an arbitrary shape. For field applications, however, it is necessary to verify the accuracy and consistency of this method. Therefore, in this study, we investigate the effects of several factors on the accuracy of the stress intensity factors obtained using the abovementioned alternating method. The obtained stress intensity factors are compared with the known values provided in handbooks, especially in the case of internal and external circumferential semi-elliptical surface cracks. The results show that the SGBEM-FEM alternating method yields accurate stress intensity factors for three-dimensional cracks, including internal and external circumferential surface cracks and that the method can be used as a robust crack analysis tool for solving field problems.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.1
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• pp.30-45
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• 2013

The present work focuses on the unsteady aerodynamics and aeroelastic properties of a small-medium sized wind-turbine blade operating under ideal conditions. A tapered/twisted blade representative of commercial blades used in an experiment setup at the National Renewable Energy Laboratory is considered. The aerodynamic loads are computed using Computational Fluid Dynamics (CFD) techniques. For this purpose, FLUENT$^{(R)}$, a commercial finite-volume code that solves the Navier-Stokes and the Reynolds-Averaged Navier-Stokes (RANS) equations, is used. Turbulence effects in the 2D simulations are modeled using the Wilcox k-w model for validation of the CFD approach. For the 3D aerodynamic simulations, in a first approximation, and considering that the intent is to present a methodology and workflow philosophy more than highly accurate turbulent simulations, the unsteady laminar Navier-Stokes equations were used to determine the unsteady loads acting on the blades. Five different blade pitch angles were considered and their aerodynamic performance compared. The structural dynamics of the flexible wind-turbine blade undergoing significant elastic displacements has been described by a nonlinear flap-lag-torsion slender-beam differential model. The aerodynamic quasi-steady forcing terms needed for the aeroelastic governing equations have been predicted through a strip-theory based on a simple 2D model, and the pertinent aerodynamic coefficients and the distribution over the blade span of the induced velocity derived using CFD. The resulting unsteady hub loads are achieved by a first space integration of the aeroelastic equations by applying the Galerkin's approach and by a time integration using a harmonic balance scheme. Comparison among two- and three- dimensional computations for the unsteady aerodynamic load, the flap, lag and torsional deflections, forces and moments are presented in the paper. Results, discussions and pertinent conclusions are outlined.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.79-87
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• 1991

An efficient numerical procedure for material and geometric nonlinear analysis of reinforced concrete shells under monotonically increasing loads through their elastic, inelastic and ultimate load ranges is developed by using the finite element method. The 8-node Serendipity isoparametric element developed by the degeneration approach including the transverse shear deformation is used. A layered approach is used to represent the steel reinforcement and to discretize the concrete behavior through the thickness. The total Lagrangian formulation based upon the simplified Von Karman strain expressions is used to take into account the geometric nonlinearity of the structure. The material nonlinearities are taken into account by comprising the tension, compression, and shear models of cracked concrete and a model for reinforcement in the concrete; and also a so-called smeared crack model is incorporated. The steel reinforcement is assumed to be in a uniaxial stress state and is modelled as a smeared layer of equivalent thickness. This method will be verified a useful tool to account for geometric and material nonlinearities in detailed analysis of reinforced concrete concrete shells of general form through numerical examples of the sequential paper( ).

• Journal of Sasang Constitutional Medicine
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• v.25 no.4
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• pp.306-319
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• 2013

Objectives The purpose of this study was to find correlations between gastrointestinal disorders, pain, sleep disorder, fatigue, and to figure out characteristics of fatigue in Sasang Constitution using medical devices data. Methods Sixty three subjects were divided into fatigue group and non-fatigue group, both groups had to undergo blood tests, questionnaire, Sasang constitutional analysis tool (SCAT), pulse wave analyzer examination, heart rate variability examination, nail fold capillary microscopic examination. Results 1) The results of questionnaire about fatigue, gastrointestinal disorder, pain, sleep disorder, quality of life had significant differences between fatigue and non-fatigue groups. 2) Soeumin had more serious gastrointestinal problem and Soyangin had more serious sleep disorder in fatigue groups than non-fatigue groups. 3) According to blood test results, there was no difference between fatigue and non-fatigue groups. 4) Elastic parameter of pulse wave analyzer and nail fold capillary microscopic examination showed significant differences between fatigue and non-fatigue groups in Soyangin. Conclusions We reach the conclusion that fatigue is usually accompanied by gastrointestinal disorder, pain, sleep disorder, deterioration in the quality of life. In Soeumin, treating gastrointestinal disorders can be helpful for treatment of fatigue. In Soyangin, improving sleep disorder may be more effective way to treat fatigue.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.10a
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• pp.133-138
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• 1991

The aim of the present paper is to develop a computer program predicting ultimate fracture strength of initially cracked structure under monotonically increasing external loads. For this purpose, two kinds of 3-D isoparametric solid elements, one 6-node wedge element and another 8-node brick element are formulated along the small deformation theory. Plasticity in the element is checked using von Mises' yield criterion. Elasto-plastic stiffness matrix of the element is calculated taking account of strain hardening effect. If the principal strain at crack tip which is one nodal point exceeds the critical strain dependin on the material property, crack tip is supposed to be opened and the crack tip node which was previously constrained in the direction perpendicular to the crack line is released. After that, the crack lay be propagated to the adjacent node. Once a crack tip node is fractured, the energy of the newly fractured node should be released which is to be absorbed by the remaining part. The accumulated reaction force which was carried by the newly fractured node so far is then applied in the opposite direction. During the action of crack tip relief force, since unloading may be occured in the plastic element, unloading check should be made. If a plastic element unloads, elastic stress-strain equation is used in the calculation of the stiffness matrix of the element, while for a loading element, elasto-plastic stress-strain equation is continuously used. Verification of the computer program is made comparing with the experimental results for center cracked panel subjected to uniform tensile load. Also some factors affecting ultimate fracture strength of initially cracked plate are investigated. It is concluded that the computer program developed here gives an accurate solution and becomes useful tool for predicting ultimate fracture load of initially cracked structural system under monotonically increasing external loads.

• International Journal of Highway Engineering
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• v.18 no.4
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• pp.37-45
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• 2016

PURPOSES : The objective of this study was to develop an impact resonance (IR) test procedure for thin disk-shaped specimens in order to determine the ${\mid}E^*{\mid}$ and phase angle values of various asphalt mixtures. METHODS : An IR test procedure was developed for evaluating thin disk-shaped specimens, in order to determine the dynamic modulus (${\mid}E^*{\mid}$) of various asphalt mixtures. The IR test method that was developed to determine the elastic modulus values of Portland cement concrete was evaluated, which method uses axisymmetric flexural vibration proposed by Leming et al. (1996). The IR tests were performed on three different mixtures of New York with varying nominal maximum aggregate sizes (NY9.5, NY19, and NY25) at six different temperatures ($10-60^{\circ}C$). The ${\mid}E^*{\mid}$ values obtained from the IR tests were compared with those determined by the commonly used AASHTO T342-11 test. RESULTS AND CONCLUSIONS : The IR test method was employed to determine the ${\mid}E^*{\mid}$ values of thin-disk-shaped specimens of various asphalt mixtures. It was found that the IR test method when used with thin disk-like specimens is a simple, practical, and cheap tool for determining the ${\mid}E^*{\mid}$ values of field cores. Further, it was found the ${\mid}E^*{\mid}$ values obtained from the IR tests using thin disk-like specimens were almost similar to those obtained using the AASHTO T342-11 test.

• Archives of Plastic Surgery
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• v.35 no.5
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• pp.626-629
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• 2008

Purpose: We investigate the possibility of vessel preservation with glycerol and evaluate the potential of preserved gastroepiploic artery as a tool for the microsurgical practice. Methods: In 5 early gastric cancer patients, IRB(No. C-0603-040-170), we gained gastroepiploic artery specimens(5 segments, about 10 cm) after gastrectomy. Each segment was rinsed in a normal saline and subsequently placed in a bottle, containing 50 mL anhydrous glycerol (87%). The bottles were refrigerated at $4^{\circ}C$, the longest preservation time being 5 months. Results: At first glance, no fragmentation was detected and the surface of vessel seemed mild sclerotic. In histological examination, vascular structures remained intact though preservation with glycerol led to a mild atrophy of the smooth muscle in the tunica media. Especially, we found out the elastic fibers and endothelial lining of the intima were preserved until 5 months. Adequate status for using microsurgical practice was also maintained and leakage test was performed successfully with gentian violet ink. Conclusion: Based on the results obtained in this study, the gastroepiploic artery preservation with glycerol as a training model for microvascular anastomosis is a technically very simple procedure and useful for the novice microsurgeon.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.11-20
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• 1993

Nonlinear inelastic behavior of an HP saddle shell has been examined by a finite element computer program developed on a Cray Y-MP. The mesh convergence is studied using three progressively refined finite element mesh models, $16{\times}16$, $32{\times}32$ and $64{\times}64$, for the elastic and inelastic analyses. It is shown that the $32{\times}32$ mesh model gives a solution that is very close to that given by the $64{\times}64$ mesh model, thus, showing a convergence. The inelastic analysis shows that the shell has a tremendous capacity to redistribute the stresses. At the ultimate, the concrete cracks and the reinforcement yieldings are spread out all over the shell, indicating that the stress distribution in the shell is approaching that given by the classical membrane theory. The present computer program provides a very useful tool for evaluating the nonlinear ultimate behavior of concrete shells during the design process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.695-700
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• 2010

Material properties of the lock plate, which covers the gas-turbine blade, are studied using ultrasonic guided waves. The lock plate is a crucial part of a gas-turbine power plant. The wave velocity and attenuation coefficient are measured to investigate the changes in the material properties under three heat-treatment conditions. Compared to the destructive mechanical tests, the material characterization of Inconel X-750 can be performed more efficiently and nondestructively by using ultrasonic guided waves; this characterization helps identify the changes occurring in its elastic moduli and Poisson's ratio under different heat-treatment conditions. The wave velocity and hardness of Inconel X-750 are proportional to each other. This nondestructive technique for the measurement of material properties can be widely used in various industries to avoid catastrophic failure. It is also expected that the guided-wave technique can be applied as a new cost- and time-saving inspection tool for longer and wider inspection ranges.