• Journal of the Korean Society for Heat Treatment
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• v.18 no.5
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• pp.297-304
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• 2005

This study was performed to determine the repair weldability of the damaged Ni type superalloy used for gas turbine blade. The experimental works included the evaluation of the microstructures of the damaged blade, selection of the repair welding procedure, characterization of repair weldment and finding the heat treatment procedures for repaired weldment. The morphology of the microstructure for the base metal was composed of austenite matrix with cubical ${\gamma}^{\prime}$ phase, MC type coarse precipitates located within grain and fine $M_{23}C_6$ type precipitates decorated at grain boundaries. The repair welding process using 90 amp current exhibited the best weld properties showing no weld microcracks. The solution and aging heat treatments of the repaired weldment could recover the original service properties of the damaged blade.

• 연구논문집
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• s.23
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• pp.15-27
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• 1993

The single crystal specimens were solidified by modified Bridgeman method. The surface recrystallized single crystal specimens were prepared by shot peening followed by heat treatment. The surface recrystallization begins at the dendrite cores on the surface. The recrystallized grains grew into the inner side of the specimen. The growth of recrystallized grains was inhibited by the pores and eutectic phases. The primary $\gamma'$ phases were dissolved at the recrystallized grain boundaries during the grain growth. The grain growth of recrystallized grains was similar to the cellular type transformation. No orientation relationships were found bewteen the recrystallized grains and the parent phase.

• Journal of the Korean Society for Railway
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• v.5 no.1
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• pp.48-54
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• 2002

This research estimated decreased vibration level as quantitative according to change of track system on Seoul Subway Line No. 1 from existing ballasted track system(Pandrol type clip) to concrete track system(Youbgdan type isolation rubber clip). Following change to concrete system, vibration level at tunnel floor decreased between 4-8dB(V). Vibration equations suggested in this paper consider the velocity of train and can estimate quantitative vibration response. These are divided by ultimate limit state($\beta$=0), serviceability limit state($\beta$=1.28) and safety state($\beta$=3), respectively. The reliability index, $\beta$=0, means 50％ data line obtained by least squares best-fit line. The reliability index $\beta$=1.28 and 3 represent boundaries below 90％ and 99.9％ respectively.

• Journal of the Korean Statistical Society
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• v.27 no.4
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• pp.515-529
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• 1998

Burman (1987) and Hall and Titterington (1987) studied kernel smoothing for sparse multinomial data in detail. Both of their estimators for cell probabilities are sparse asymptotic consistent under some restrictive conditions on the true cell probabilities. Dong and Simonoff (1994) adopted boundary kernels to relieve the restrictive conditions. We propose a local linear kernel estimator which is popular in nonparametric regression to estimate cell probabilities. No boundary adjustment is necessary for this estimator since it adapts automatically to estimation at the boundaries. It is shown that our estimator attains the optimal rate of convergence in mean sum of squared error under sparseness. Some simulation results and a real data application are presented to see the performance of the estimator.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.31B no.5
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• pp.141-148
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• 1994

Both the neural network classifier utilizing multi-layer perceptron and the linear tree classifier composed of hierarchically structured linear discriminating functions can form arbitrarily complex decision boundaries in the feature space and have very similar decision making processes. In this paper, a new method for automatically choosing the number of neurons in the hidden layers and for initalzing the connection weights between the layres and its supporting theory are presented by mapping the sequential structure of the linear tree classifier to the parallel structure of the neural networks having one or two hidden layers. Experimental results on the real data obtained from the military ship images show that this method is effective, and that three exists no siginificant difference in the classification acuracy of both classifiers.

• Korean Journal of Child Studies
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• v.26 no.2
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• pp.43-53
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• 2005

The purpose of this study was to investigate children's acquisition of cardinality in terms of a framework that isolates two cognitive components, analysis of knowledge and control of processing. The subjects were 30 4-and 5- year-olds who were asked to solve three problems that required an understanding of cardinality. The problems were designed to place different demands on these processing components on the tasks than the 4-year-olds and correlastion among scores on the three tasks show that there is no correlation between the tower task assessing control and the two tasks that assessed analysis. The implications of the results are that aspects of symbolic development may be a broadly based process that extends beyond domain-specific boundaries.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.411-418
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• 2004

Using a level set method we develop a shape optimization method applied to energy flow problems in steady state. The boundaries are implicitly represented by the level set function obtainable from the 'Hamilton-Jacobi type' equation with the 'Up-wind scheme.' The developed method defines a Lagrangian function for the constrained optimization. It minimizes a generalized compliance, satisfying the constraint of allowable volume through the variations of implicit boundary. During the optimization, the boundary velocity to integrate the Hamilton-Jacobi equation is obtained from the optimality condition for the Lagrangian function. Compared with the established topology optimization method, the developed one has no numerical instability such as checkerboard problems and easy representation of topological shape variations.

• 연구논문집
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• s.29
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• pp.163-171
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• 1999

A new titanium alloy system. Ti-xFe-ySi (x,y=0-4 wt%). was designed and characterized with the point at low cost and high strength for casting applications. Fe improved room and elevated temperature mechanical properties owing to solid solution hardening and beta phase stabilization. Si yielded titanium silicides and Si addition over 1 wt% resulted in poor ductility due to coarse silicide chains at prior beta boundaries. The optimum composition was found to be Ti-4Fe-(0.5-1)Si in the viewpoint of tensile strength and ductility which are comparable to the Ti-6Al-4V. The metal-mould reaction was also examined for Ti-xFe and Ti-xSi binary alloy system. The thickness of surface reaction layer w as not affected significantly with Fe content, while it was decreased with Si content. In the Ti-4Si alloy, no reaction layer was found. The depth of surface hardening layer was about $200\mum$ regardless of the mould materials.

• Journal of Welding and Joining
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• v.13 no.3
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• pp.89-95
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• 1995

Effect of boron on corrosion resistance of Type 304 stainless steel has been studied. Boron tends to segregate at the grain boundaries during cooling after solution treatment, and so boron treated steel usually exhibits a ditch structure under the 10% oxalic acid test. However, it was found that the addition of 25 ppm boron in Type 304 steel has no effect on the general and pitting corrosion resistance while it has a little effect on the intergranular corrosion resistance.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1040-1047
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• 2008

Hypoid gears are widely used in rear drive and 4WD vehicle axles. Investigation of their sensitivity to deflections is one of the most important aspects of their design and optimization procedures. The deflection test is performed in the actual gear mounting using completely processed gear. This test should cover the full operating range of gear loads from no load to peak load. Under peak load the contact pattern should extend to the tooth boundaries without showing a concentration of the contact pattern at any point on the tooth surface. Transmission error is tested on an axle assembly triaxial real car load condition.