• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.924-931
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• 2002

Vacuum interrupters in order to be used in various switch-gear components such as circuit breakers, distribution switches, contactors, etc. spread the arc uniformly over the surface of the contacts. The electrodes of vacuum interrupters are made of sinter-forged Cu-Cr materials for good electrical and mechanical characteristics. Since the closing velocity is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at the high strain rate is obtained from the split Hopkinson pressure bar test using disc-type specimens. Experimental results from both quasi-static and dynamic compressive tests are Interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the value of five parameters such as the initial velocity of a movable electrode, the added mass of a movable electrode, the wipe spring constant, initial offset of a wipe spring and the virtual fixed spring constant.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.939-951
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• 2002

We propose a new multiscale Galerkin method based on interpolation wavelets for two-dimensional Poisson's and plane elasticity problems. The major contributions of the present work are: 1) full multiresolution numerical analysis is carried out, 2) general boundaries are handled by a fictitious domain method without using a penalty term or the Lagrange multiplier, 3) no special integration rule is necessary unlike in the (bi-)orthogonal wavelet-based methods, and 4) an efficient adaptive scheme is easy to incorporate. Several benchmark-type problems are considered to show the effectiveness and the potentials of the present approach. is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at the high strain rate is obtained from the split Hopkinson pressure bar test using disc-type specimens. Experimental results from both quasi-static and dynamic compressive tests are Interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the value of five parameters such as the initial velocity of a movable electrode, the added mass of a movable electrode, the wipe spring constant, initial offset of a wipe spring and the virtual fixed spring constant.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.6
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• pp.821-826
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• 2013

When the values of design variables change, mode switching can often occur. If the mode of interest is not tracked, the frequencies and modes for design optimization may be miscalculated owing to modes that differ from the intended ones. Thus, mode tracking must be employed to identify the frequencies and modes of interest whenever the values of design variables change during optimization. Furthermore, reliability-based design optimization (RBDO) must be performed for design problems with design variables containing uncertainty. In this research, we perform RBDO considering the mode tracking of a compressive coil spring, i.e., a component of the joint spring that supports a compressor, with design variables containing uncertainty by using only kriging metamodels based on multiple responses approach (MRA) without existing mode tracking methods. The reliability analyses for RBDO are employed using kriging metamodel-based Monte Carlo simulation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.616-624
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• 2014

Most of oven range doors are opened from top to down. Feeling of door in case of home appliances including oven ranges affects the quality of product. The major factors to evaluate the feeling quality are opening force, closing force, and bouncing effect happened when the door is opened completely. If opening and closing forces become large, consumers may have complaints. If the bouncing effect becomes large, the impact can cause the body as well as the door to damage. Opening and closing forces, and bouncing effect must be minimized to improve the feeling quality. In this study, the mechanism which improves the existed dual compressive spring and cam structure is suggested by using nonlinear cam and spring. After the nonlinear cam is designed and manufactured for the suggested mechanism, this cam is confirmed to become more superior than the existed one by applying it to the practical oven range.

• Journal of Ocean Engineering and Technology
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• v.18 no.5
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• pp.43-49
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• 2004

The lightness of components required in the automobile and machine industry necessitates the use of high strength components. In particular, the fatigue failure phenomena, which occurs when using metal, increases the danger to human life and property. Therefore, antifatigue failure technology is an integral part of current industries. Currently, the shot peening is used for removing the defect from the surface of steel, while improving the fatigue strength on surface. Therefore, in this paper, the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in a stress ratio(R=0.1, R=0.3, R=0.6) was investigated, giving consideration to fracture mechanics. By using the methods mentioned above, following conclusions are drawn: (1) The fatigue crack growth rate(da/dN) of the shot-peening material was lower than that of the un-peening material and in stage I, ΔKth, the threshold stress intensity factor of the shot-peen processed material is high in critical parts, unlike the un-peening material. Also m, fatigue crack growth exponent and number of cycle of the shot-peening material, was higher than that of the un-peening material, as concluded from effect of da/dN. (2) Fatigue life shows more improvement in the shot-peening material than in the un-peening material, and the compressive residual stress of surface on the shot-peen processed operate resistance of fatigue crack propagation.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.3
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• pp.17-23
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• 2005

In this study, the high strength and superior toughness spring steels as the suspension material, used for automobile and railroad industries were utilized to carry out the following investigations. Corrosion times were controlled in 7, 14,30 and 60days to examine the relation between corrosion pit and compressive residual stress in the static corrosion environment after shot peened. And then corrosion current and corrosion potential were measured for every 24 hours to investigate the corrosion mechanism. Shot peened material shows the low or rate of corrosion current as compared with unpeened material. In case of hot peened material which has the highest residual stress, it has a low corrosion current density.

• Journal of the Korean institute of surface engineering
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• v.35 no.6
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• pp.357-362
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• 2002

In this study, to improve the effect of the surface treatment, the shape design of shot ball is proposed. The fatigue effects of shot peening by the cut wire shot ball and the rounded cut wire shot ball are compared. The rotary bending and tensile fatigue tests are conducted on a spring steel to evaluate fatigue lives. The residual compressive stresses by the rounded cut wire shot ball is higher than by the rounded cut wire shot ball. This consequently increase the fatigue life and the reliability of surface treatment. Thus, to obtain optimum, repeatable and reliable shot peening effect the shape of the shot ball must be round.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1181-1192
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• 2015

In this paper, an analytical method is proposed to study the effect of crack and axial load on vibration behavior and stability of the cracked columns. Using the local flexibility model, the crack has been simulated by a torsional spring with connecting two segments of column in crack location. By solving governing eigenvalue equation, the effects of crack parameters and axial load on the natural frequencies and buckling load as well as buckling load are investigated. The results show that the presents of crack cause to reduction in natural frequencies and buckling load whereas this reduction is affected by the location and depth of the crack. Furthermore, the tensile and compressive axial load increase and decrease the natural frequencies, respectively. In addition, as the compression load approaches to certain value, the fundamental natural frequency reaches zero and instability occurs. The accuracy of the model is validated through the experimental data reported in the literature.

• Smart Structures and Systems
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• v.24 no.6
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• pp.683-692
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• 2019

Traditional damage detection methods for nonlinear structures are often based on simplified models, such as the mass-spring-damper and shear-building models, which are insufficient for predicting the vibration responses of a real structure. Conventional global nonlinear finite element model updating methods are computationally intensive and time consuming. Thus, they cannot be applied to practical structures. A decentralized approach for identifying the nonlinear material parameters is proposed in this study. With this technique, a structure is divided into several small zones on the basis of its structural configuration. The unknown material parameters and measured vibration responses are then divided into several subsets accordingly. The structural parameters of each subset are then updated using the vibration responses of the subset with the Newton-successive-over-relaxation (SOR) method. A reinforced concrete and steel frame structure subjected to earthquake loading is used to verify the effectiveness and accuracy of the proposed method. The parameters in the material constitutive model, such as compressive strength, initial tangent stiffness and yielding stress, are identified accurately and efficiently compared with the global nonlinear model updating approach.

• Journal of the Korean Institute of Gas
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• v.11 no.4
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• pp.85-90
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• 2007

This paper presents the finite element analysis on the strength safety of a full containment LNG storage tank system with damping safety structures. For the FEM analysis of the inner tank, the combined loads in which are related to a hydrostatic pressure, a cryogenic temperature load, BOG pressure, LNG weight, and a sinking force at the comer of the inner tank have been applied to the inner tank structure. The FEM computed results show that the conventional inner tank is safe for the given combined loads, but the damping safety structure such as compressive springs may be more useful structures to increase the safety of the tank system. The increased stiffness and the appropriate position of the springs are very important design parameters for increasing the damping strength safety of the tank system.