• Journal of the Korean Ceramic Society
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• v.30 no.5
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• pp.404-410
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• 1993

The characterization and sintering behavior of ZnO powders prepared by precipitation method were investigated. ZnO powders were synthesized using the aqueous solutions of ZnCl2 and NH4OH as a precipitation agent, which were crystallized in the shape of plate-like. The grain growth of ZnO(0.68${\mu}{\textrm}{m}$, 1.3${\mu}{\textrm}{m}$ and 3.4${\mu}{\textrm}{m}$) has been studied for temepratures from 100$0^{\circ}C$ to 130$0^{\circ}C$, and the rate of densification was inversely proportional to the ZnO particle size. Densification proceeded slowly by diffusion mechanisms above at 100$0^{\circ}C$. In this work, the grain growth kinetic exponent(n) was 3. The temperature dependence of ZnO grain growth was plotted, and the activation energy of grain growth was 75~85Kcal/mol.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.2
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• pp.43-49
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• 2005

The purpose of a fatigue crack arrest design is to prevent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flanges, crack arrest is possible; arrest occurring when the fatigue crack reaches the second element. In the present work, a numerical analysis was carried out to estimate the effect of shape parameters on fatigue crack growth and arrest behavior of integrally stiffened panels. Based on these results, a set of fatigue crack arrest design chart is presented as "non-dimensional arrest load - thickness ratio" relationship.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.521-527
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• 1997

Irregular shapes and growth behavior of surface micro-crack showed very complex and nonlinear propeties and many investigators have performed theoretical analysesand experiments on them to characterize fatigue strength. They had difficulties in estimating fatigue life due to random distribution, growth and coalescence of surface micro-cracks. The straightness of crack growth along intergranular and transgranular was prevented from irregular microstructure and precipitates. Euclid geometry can't quantify shape of surface micro-crack but ftractal geometry can. Therefore, it is suggested that average fractal dimension of surface micro-cracks is able to estimate fatigue life but fractal dimension of maximum surface micro-crack is not in Al 2024-T3 alloy.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.5 no.3
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• pp.31-39
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• 1996

The objective of this study is to investigate the influence of welding residual stresses on the fatigue crack growth behavior of cracks located transverse to the weld bead. For this purpose, G. T. A (Gas Tungsten Arc) welding was performed on hte Al alloy 1100-O plate and the same initial crack is made on HAZ(Heat Affected Zone), weld metal and base meta respectively. Specimens were used CT(Compact Tension) specimens. Initial welding residual stresses were measured by using strai gage sectioning method. All specimens were tested under constant amplitude load with stress ratio R=0.1, It is possible to predict fatigue crack growth behaviors and the fatigue life, using numerical analysis together with distribution of initial residual stress and the values of C and m obtained from $da/dN-{\Delta}K$

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2237-2242
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• 2011

Anomalous scaling behaviors such as significantly large growth exponent (${\beta}$) and small reciprocal of dynamic exponent (1/z) values for many molecular crystalline thin films have been reported. In this study, the variation of scaling exponent values and consequent growth behaviors of molecular thin films were more quantitatively analysed using a (1+1)-dimensional surface lateral diffusion model. From these simulations, influence of step edge barriers and grain boundaries of molecular thin films on the various scaling exponent values were elucidated. The simulation results for the scaling exponents were also well consistent with the experimental data for previously reported molecular thin film systems.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.28-31
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• 1998

Wrinkling is one of the major defects in sheet metal products and may be also attributable to the wear of the tool. The initiation and growth of the wrinkles are influenced by many factors such as stress state, mechanical properites of the sheet material, geometry of the body, and contact condition. It is difficult to analyze the wrinkling initiation and growth considering the factors because the effects of the factors are very complex and the wrinkling behavior may show wide variation for small deviation of the factors. In this study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth, All the above mentioned factors are conveniently considered by finite element method. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. The finite element analysis is carried out using the continuum-based resultant shell elements considering the planar anisotropy of the sheet metal. The proposed method is verified by employing to column buckling problem. And then, the initiation and growth of wrinkling in deep drawing of cylindrical cup are analyzed.

• Journal of the Korean Home Economics Association
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• v.41 no.11
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• pp.171-187
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• 2003

The purpose of this study was to measure the effects of self-growth group counseling program for children in a group home. The results of this study are as follows. First, the self-growth group counseling program was effective to improve self esteem. The most significant increases were seen in the global self-esteem and school-academic self-esteem. Second, the group cohesion and participation frequency of the program were improved, as the session was progressed. Third, as the changes of individual, the understanding and acceptance of oneself and the others are improved. So, impulsivity and aggression became lower, and problem behavior was less.

• 연구논문집
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• s.25
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• pp.175-184
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• 1995

Mechanical properties of the gas nitrocarburized product depend on the surface compound layer and the diffusion zone formed. The compound layer improves the wear resistance, and the corrosion resistance. Though phase composition, pore layer and growth rate of the compound layer varies according to the treatment time, temperature and the kind of the steel substrate, they are strongly influenced by the environmental gas composition. In the current study, the growth behavior of the compound layer and diffusion zone of the carbon steel and the alloy steel upon nitrocarburizing treatment at $570^{\circ}C$, and the phase composition and the variation in the growth rate of the compound layer according to the variation of the gas environment which was the medium of the nitriding and carburizing reaction were investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.577-584
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• 2003

A crack with growth in ferroelectric ceramics under purely electric loading is analyzed. The crack tip stress intensity factor for the growing crack under small-scale conditions is evaluated by employing the model of nonlinear domain switching. The crack tip stress intensity factor increases or decreases with crack growth, depending on the electrical nonlinear behavior and the direction of an applied electric field. It is shown that the ferroelectric material can be either toughened or weakened as the crack grows. The steady state crack growth in ferroelectric ceramics is also discussed.

• Korean System Dynamics Review
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• v.1 no.1
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• pp.29-56
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• 2000

During the past few years, cyberspace and electronic commerce has been expanding throughout the world rapidly. The purpose of this paper is to find out policy leverages for boosting up cyberspace and electronic commerce using system dynamics simulation modeling approach. The system dynamics simulation model developed in this paper allows analysis of both the effect of factors on dynamic growth pattern of cyberspace as well as the effect of time delay in information processing, money transfer and delivery on model behavior. Finding of this study is that capacity of information infrastructure and size of cyberspace population are key factors of cyberspace growth. Also, reducing time delay in information flow, money flow, and delivery flow is an important policy leverages for growth of electronic commerce.