• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.634-645
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• 2008

In this study, surface composites were fabricated with Fe-based amorphous alloy powders and VC powders by high-energy electron beam irradiation, and the correlation of their microstructure with hardness and fracture toughness was investigated. Mixture of Fe-based metamorphic powders and VC powders were deposited on a plain carbon steel substrate, and then electron beam was irradiated on these powders without flux to fabricate surface composites. The composite layers of 1.3~1.8 mm in thickness were homogeneously formed without defects and contained a large amount (up to 47 vol.%) of hard $Cr_2B$ and $V_8C_7$ crystalline particles precipitated in the solidification cell region and austenite matrix, respectively. The hardness of the surface composites was directly influenced by hard $Cr_2B$ and $V_8C_7$ particles, and thus was about 2 to 4 times greater than that of the steel substrate. Observation of the microfracture process and measurement of fracture toughness of the surface composites indicated that the fracture toughness increased with increasing additional volume fraction of $V_8C_7$ particles because $V_8C_7$ particles effectively played a role in blocking the crack propagation along the solidification cell region heavily populated with $Cr_2B$ particles. Particularly in the surface composite fabricated with Fe-based metamorphic powders and 30 % of VC powders, the hardness and fracture toughness were twice higher than those of the surface composite fabricated without mixing of VC powders.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.1
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• pp.22-28
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• 2004

Since the used materials of furnace heater tube with different kinds of thermal degradation were not commonly available, the HK-40 steel specimens were heat-treated isothermally at elevated temperature to simulate the microstructure at the service temperature. HK-40 steel specimens with five different aging time were prepared by isothermal heat treatment at $1050^{\circ}C$. The characteristics of the magnetic susceptibility have been investigated for the degradation evaluation of HK-40 steel. The magnetic susceptibility at room temperature increases as the extent of degradation of the materials increases. The variation of magnetic susceptibility was compared with the variation of tensile properties and Vickers hardness. To investigate the effect of the microsturctural change on the characteristics of tensile properties, hardness and magnetic susceptibility, the microstructures were examined by a scanning electron microscope(SEM) and the chemical compositions were analyzed by a energy spectrometer of SEM. As a result, the magnetic susceptibility method can be suggested as one of the nondestructive evaluation methods for the degradation of the HK-40 steel.

• Journal of the East Asian Society of Dietary Life
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• v.8 no.4
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• pp.454-461
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• 1998

This study was conducted to aerermine the sensory evaluation and the texture characteristics after making greentea Sulgidduk and Julpyun added to greentea powder in according to concentration which has nutritive value and medical effect of white Sulgidduk and Julpyun traditional dduk. Greentea Julpyun was better evaluated than Sulgidduk in color, flavor, hardness, chewiness and overall quality as the result of the sensory evaluation. In the whole sensory Julpyun was highly evaluated at the 3% of concentration of greentea powder but Sulgidduk was highly evaluated at 7% as the concentration of the greentea powder was getting stronger and stronger. In case of texture analysis hardness, cohesiveness, gumminess and chewiness of greentea Julpyun were getting lower by increase of concentration of greentea powder. The hardness, springiness, gumminess and chewiness of greentea Sulgidduk were lower by increase of concentration of greentea too. As the result of the measurement with texture analyser, Sulgidduk was lower than greentea Julpyun in the hardness, springiness, cohesiveness, gumminess and chewiness. As the result of the values of Hunter color system, the lightness and redness of greentea Julpyun were the lowest when nothing was added. The lightness and redness of greentea Sulgidduk were the highest in nothing added group. The yellowness was the highest at 3% of added greentea amount The resuts of correlation between the sensory properties and texture properties of greentea Julpyun showed that flavor described the lightness of measurement through texture and negative correlation, yellowness described positive correlation.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.99-107
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• 1999

Boiler high-temperature pipelines such as main steam pipe, header and steam drum in fossil power plants are degraded by creep damage due to severe operationg conditions which are high temperature and high pressure for an extended period time. Such material degradation leads to various component failures causing serious accidents at the plants. Conventional measurement techniques such as replica method, electric resistance method, and hardness test method have such disadvantages as complex preparation and measurement procedures, too many control parameters, and therefore, low practicality and they were applied only to component surfaces with good accessibility. In this paper, artificial creep degradation test and ultrasonic measurement for their creep degraded specimens have been carried out for the purpose of evaluation for creep damage which can occur in high-temperature pipeline of fossil power plant. Absolute measuring method of quantitative ultrasonic measurement for material degradation was established, and long term creep degradationtests using life prediction formula were carried out. As a result of ultrasonic tests for crept specimens, we confirmed that the sound velocity decreased and the attenuation coefficient linearly increased in proportion to the increase of creep fractiin(${\phi}$c).

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.7 no.3
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• pp.110-114
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• 2008

In this study, to examine the friction coefficient and wear amount of dental prosthesis, pin-on-disk type wear test were at room temperature. Vickers hardness and fracture toughness measurement of dental materials were preformed. Microscopic observations on worn surfaces of specimens were conducted by SEM. The friction coefficient of dental material was investigated according to weight and slinging velocity. dental material have investigated composed to nature teeth.

• Journal of the Korean Society of Safety
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• v.9 no.4
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• pp.11-16
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• 1994

Acoustic emission technique is applied to the fatigue crack initiation in a carburized gear tooth. Acoustic emission test performed on carburized gear and three-point bending test equal to carburized gear hardness. The marked acoustic emission are detected at the early stage of crack initiation measured by a crack gauge and the final stage just before the tooth failure. The estimated acoustic emission energy rate are characteristic of the measured acoustic emission.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1000-1004
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• 2007

Thermal cracks are among the key factors that control the quality of a brake disk. Thermal cracks may shorten the lifetime of the disc and increase brake noise. Therefore, high heat-resistant brake disk materials are needed. In this study, three kinds of disk material were tested. They are composed of C, Si, Mn, P, S, Cu, Cr, Mo, and Ni. For the three materials, tensile tests, hardness measurement, metallurgical structure analysis, image analyzer analysis, etc were carried out. And friction tests were performed by a small scale dynamometer.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.142-142
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• 2004

박막으로 표면처리한 다양한 강판이 자동차 차체와 부품, 가전제품 등의 제조를 위해 여러 가지 판재 성형공정에 적용되고 있으나, 제품 개발기간과 비용 감소, 성형과정에서 표면 코팅층의 특성 변화로 인해 성형성 열화와 성형불량을 줄이면서, 제품의 고정밀화, 고품질화를 실현하기 위해서는 코팅층에 대한 기계적 특성과 마찰거동을 명확히 규명하는 것이 반드시 필요하다 현재 나노 마이크로 수준인 코팅층의 기계적 물성치를 측정하기 위해 가장 널리 사용되는 방법은 나노 인덴테이션이다.(중략)

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• v.10 no.1
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• pp.274-280
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• 2005

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• v.10 no.1
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• pp.29-36
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• 2005