• Korean Journal of Materials Research
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• v.9 no.4
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• pp.335-340
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• 1999

The hot cracking phenomena and phase behaviors during hot working process of Cu-Ni bearing hot rolled steels were investigated by a $90^{\circ}$bending tests, BSE image analysis and EDS analysis. For aNi-free 1.2% Cu bearing steel, the surface hot cracking occurred about $1100^{\circ}C$ due to a liquid state Cu-enriched phase formed continuously at the interface between oxide scale and matrix. The liquid Cu-enriched phase penetrated into austenite grain boundaries and caused surface cracking during the hot working. In case of 0.6% Ni containing 1.2% Cu-Ni bearing steel, solid state Cu-Ni-riched phase existed at the scale/matrix interface as a discontinuous type. But the higher addition of 1.2% Ni, solid state Ni-Cu-riched phase was formed dominantly in the oxide scale. It was found that the addition of Ni suppressed the surface cracking of 1.2% Cu bearing steel by eliminating the liquid state Cu-enriched phase.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.29 no.1
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• pp.275-282
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• 1999

Purpose: The objective of this study was to compare clinical examination of dental caries and secondary caries with panoramic examination. and to examine bone lesions and dental anomaly of unerupted state. Materials and Methods: In this study. clinical records and panoramic radiographs were available for 89 first grade students in elementary school. Dental caries of occlusal surfaces. proximal surfaces. and buccolingual surfaces were examined. Secondary caries was examined too. In addition. the central lesion and dental anomaly of unerupted state were examined in panoramic radiographs. Results: The obtained results were as followed: 1. Carious detectability of clinical examination in occlusal and buccolingual surface was higher than that of panoramic examination. but it is statistically insignificant(p>0.05). In proximal surface. carious detect ability of panoramic examination was higher than that of clinical examination. and it is statistically significant(p<0.01). 2. In contrast to clinical examination only. when the two examination methods were combined. there was additional detection of dental caries(26.7％ in occlusal surface. 48.2％ in proximal surface. 33.3％ in buccolingual surface. and 38.3％ totally). 3. In detection of secondary caries. panoramic examination had lower ability than clinical examination in all three surfaces. but in case that both methods were combined. totally 36.0％ extra carious lesions were detected. 4. In panoramic examination. detectability of secondary caries in upper teeth is lower than lower teeth. 5. In panoramic examination. it was possible to detect the central lesions and dental anomalies of unerupted state which cannot be detected in clinical examination. Conclusion: It is useful to combine the panoramic examination with clinical examination in order to increase carious detectability and to evaluate the central lesions and dental anomalies of unerupted state

• Journal of Powder Materials
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• v.28 no.1
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• pp.31-37
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• 2021

This study explores reducing the oxygen content of a commercial Ti-48Al-2Cr-2Nb powder to less than 400 ppm by deoxidation in the solid state (DOSS) using Ca vapor, and investigates the effect of Ca vapor on the surface chemical state. As the deoxidation temperature increases, the oxygen concentration of the Ti-48Al-2Cr-2Nb powder decreases, achieving a low value of 745 ppm at 1100℃. When the deoxidation time is increased to 2 h, the oxygen concentration decreases to 320ppm at 1100℃, and the oxygen reduction rate is approximately 78% compared to that of the raw material. The deoxidized Ti-48Al-2Cr-2nb powder maintains a spherical shape, but the surface shape changes slightly owing to the reaction of Ca and Al. The oxidation state of Ti and Al on the surface of the Ti-48Al-2Cr-2Nb powder corresponds to a mixture of TiO2 and Al2O3. As a result, the peaks of metallic Ti and Ti suboxide intensify as TiO2 and Al2O3 in the surface oxide layer are reduced by Ca vapor deposition.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.25-25
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• 2000

This paper presents a design method of sliding mode control (SMC) for single input linear systems with mismatched uncertainties. We define a virtual state based on the controllable canonical form of the nominal system. And we define a sliding surface for the augmented system with a virtual state. This sliding surface makes it possible to use SMC technique with various types of controllers. In this paper, we construct a controller that combines SMC with robust controller. We design a robust controller for the system with only mismatched uncertainties using a form of linear matrix inequality (LMI). We make a virtual state from this robust control input and the states of the nominal system. And we design a sliding mode controller that stabilizes the overall closed-loop system.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.3
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• pp.193-197
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• 2001

This paper presents a design method of sliding model control (SMC) for single input linear systems with mismatched uncertainties. We define a virtual state based on the controllable canonical form of the nominal system. And we defined a sliding surface for the augmented system with a virtual state. This sliding surface makes it possible to use the SMC technique with various types of controllers. In this paper, we construct a controller that combines SMC with robust controller. We design a robust controller for the system with mismatched uncertainties using a form of linear matrix inequality(LMI). We make a virtual state from this robust control input and the states of the nominal system. And we design a sliding model controller that stabilizes the overall closed-loop system.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2669-2671
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• 2000

In this paper, a new model error following sliding mode control is considered with a novel sliding surface for the error. This novel sliding surface has nominal dynamics of an original state of the error system and makes it possible that the Sliding Mode Control(SMC) technique for the error of the model following is used with the various types of controllers. Its design is based on the augmented system whose dynamics have a higher order than that of the original error system. The reaching phase is removed by using an initial virtual state which makes the initial error state sliding function equal to zero.

• Structural Engineering and Mechanics
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• v.58 no.4
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• pp.677-687
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• 2016

On the basis of the energy approach it is reported a development of the yield function and the constitutive equations for the orthotropic material with consideration of the crystal lattice constants and parameters of the crystallographic texture for the general stress state. For practical use in sheet metal forming analysis it is considered different loading scenarios: plane stress and plane strain states. Using the proposed yield function, the influence of single ideal components on the shape of yield surface was analyzed. The six texture components investigated here were cube, Goss, copper, brass, S and rotated cube, as these components are typically observed in rolled sheets from FCC alloys.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1327-1329
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• 2006

We give pressure stimulation into organic thin films and then manufacture a device under the accumulation condition that the state surface pressure is 2, 10, 30[mN/m](gas state, liquid state, and solid state). The physicochemical properties of the LB films on the surface of pure water are studied by AFM. Also, we then examined of the Metal-Insulator-Metal(MIM) device by means of I-V.

• Proceedings of the Korean Vacuum Society Conference
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• 1997.07a
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• pp.121-121
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• 1997

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2089-2104
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• 1995

A novel and efficient cutter path planning method for machining intricately shaped curved surfaces, called the steepest directed tree method, is presented. The curved surface is defined by triangular facets, the density and structure of which are determined by the intricacy and form accuracy of the surface. Geometrical form definition and recognition of the topological features are used to connect the nodes of the triangulated surface meshes for the successive and interconnected steepest pathways, which makes good use of end milling characteristics. The planetary cutter centers are determined to locate along smoothly changing paths and then the height values of the cutter are adjusted to avoid surface interference. Several machined examples of intersecting and intricate surfaces are presented to illustrate the benefits of the new approach. It is shown that due to more consistent geometry matching between cutter and surface(in comparison with the current CC Cartesian method) surface finish can be typically improved. Moreover, the material in concave fillets which is difficult to be removed by ball mills can be removed efficiently. The built-in positioning of cutter to avoid interference runs minutely in the sharp and discontinuous regions. The steepest upward movement of the cutter gives a stable dynamic cutting state and allows increase in the feedrate and spindle speed while remaining the stable cutting state.