• Composites Research
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• v.18 no.3
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• pp.21-30
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• 2005

Vacuum hot pressing has been used for the development of titanium metal matrix composites using foil-fiber-foil method. Heterogeneous microstructures prior to and following consolidation have been quantified, and the relations to densification behavior investigated. As shown by the results, dramatic variations of the microstructures including equiaxed $\alpha$, transformed $\beta$ and $ Widmanst\ddot{a}tten$ $\alpha$ are obtained during the process according to the fiber distributions. The dependence of microstructures on the consolidation then has been explained in terms of the change in mechanisms such as grain growth and recrystallization that occur with changing levels of inhomogeneity of deformation. Further, micro-mechanics based constitutive model enabling the evolution of density over time together with the evolutions of microstructure to be predicted has been developed. The mode developed is then implemented into finite element scheme so that practical process simulation has been carried out.

• Journal of Welding and Joining
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• v.14 no.2
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• pp.79-89
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• 1996

일정진폭하중과 과대하중비 2.5의 단일 인장과대하중에 의한 4140강 용접부 의 피로균열성장거동을 실온과 -45.deg.C의 저온에서 피로시험과 파면관찰을 통하여 고찰하였다. 이때, 용접부 미시조직의 영향을 평가하기 위해 모재(parent metal), 열영향부(as-welded HAZ), 열처리된 열영향부(PWHT HAZ)로 나누어 응력비 0과 0.5로 CT시험편을 이용하여 피로시험을 실시하였다. 피로균열성장거동은 재료의 미시조직과 온도변화보다는 응력비에 크게 영향을 받았으며, 단일 과대하중에 의한 피로균열성장 지연효과가 모든 재료에서 상당히 크게 나타났다. 전자현미경에 의한 피로파면 관찰 결과, 실온에서는 연성의 스트라이에이숀과 -45.deg.C에서는 의벽개파면과 같은 피로 균열성장거동을 나타내고 있다.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.5
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• pp.80-86
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• 2005

High velocity oxy-fuel thermally sprayed coating of the WC-Co cermet material is a well-established process for modifying the surface properties of the structural components exposed to the corrosive and wear attacks. The hard WC phase in the coating resists to the wear while the soft metallic Co increases the adhesive and cohesive bonding properties. The coating properties deposited by the HVOF process are greatly dependent on the feedstock materials and processing parameters. The effects of the feedstock material and process coating parameters including the in-flight particle parameters and resultant coating microstructures were observed in this paper.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.316-325
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• 1986

Characteristics of fatigue crack propagation in martensite-ferrite duel phase steels have been investigated. In low .DELTA.K region, fatigue crack propagation resistance increases with increasing volume fraction of martensite, but the difference of crack propagation resistance resulted from the volume fraction decreases with increasing .DELTA.K. Also, threshold stress intensity factor range .DELTA.K$_{th}$ increases with increasing volume fraction of martensite, But fatigue crack propagation rates of dual-phase steels in terms of .DELTA.K$_{eff}$ are independent to volume fraction of martensite. These phenomena can be explained by the roughness induced crack closure due to crack deflection.n.n.

• Journal of the KSME
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• v.20 no.4
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• pp.288-295
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• 1980

본고에서는 복합조직을 가진 강의 파괴기동 및 인성에 미치는 미시 crack의 형성거동의 문제에 대하여, 재료개발이라고 하는 흡금학상의 분야에 있어서 미시조지학적관점으로부터 검토하였다. 이와 같이 문제를 한정시켜도 강도, 연성 및 인성치의 평가에 대하여 통일적인 견해를 얻는 것이 대단히 어려우며, 이것은 서언에서 설명한 것과 같이 각상간의 역학적간섭효과를 충분히 검토한 후에 이해되어지리라 생각한다. 마지막으로, 이들 강의 최근의 진보 및 비노파괴기동에 대한 상 세한 상술은 다음 기회로 미루었으며, 그리고 원교의 불충분한 점이 있다고 생각되나 복합조직을 가진 강의 파괴거동 및 인성에 대하여 관심을 가지고 있는 분들에게 조금이라도 도움이 된다면 다행으로 생각하는 바이다.

• Journal of the KSME
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• v.21 no.1
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• pp.44-55
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• 1981

근년 산업의 발달에 따른 재료의 다양성때문에 구조물의 안전성 확보및 신뢰성 향상을 위하여 사용재료의 파괴방지에의 연구의 중요성이 종래에 비해서 한층 더 높아지고 있으며, 현재까지 행하여지고 있는 이들 연구를 대별하면 다음의 3가지 분야로 나눌 수 있다. 즉 제 1 은 순수형 태에서의 파괴의 본질을 결정구조나 전위론등에 기초를 두고 물성론적 입장에서 논하려고 하는 분야, 제 2 는 재료가 가진 야금학적 인자(화학성분, 미시조직인자 등)가 파괴에 미치는 영향을 미시조직학적 관점으로부터 취급하는 분야, 제 3 은 재료를 보다 거시적으로 보아서 균일한 탄 소성체로서 취급하고, 주로 역학적 관점에서 규명하는 파괴역학분야이다. 특히 20수년간 비약적인 진보를 가져온 파괴역학의 수법은 구조물의 불안정파괴에 대한 안전확보라는 견지에서 커다란 성과를 가져왔다. 파괴역학에 있어서의 흥미대상은 예나 지금이나 파괴인성(Fracture Toughness )의 문제에 향해져 있다. 본강좌에서는 파괴역학및 파괴인성의 기본적 개념에 대하여 설명함과 동시에 파괴인성의 평가법에 대해서 기술한다.

• Journal of Ocean Engineering and Technology
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• v.20 no.5 s.72
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• pp.77-81
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• 2006

In this study, monolithic liquid phase sintered SiC (LPS-SiC) was made by the hot pressing method with nano-SiC powder, whose particle size is 30 nm and less on the average. Alumina ($Al_{2}O_{3}$), yttria ($Y_{2}O_{3}$), and silica ($S_{i}O_{2}$) were used for sintering additives. To investigate the effects of $S_{i}O_{2}$, the $Al_{2}O_{3}/Y_{2}O_{3}$ composition was fixed and the ratio of $S_{i}O_{2}$ was changed, with seven different ratios tested. And to investigate the effects of the sintering temperature, the sintering temperature was changed, with $1760^{\circ}C,\;1780_{\circ}C$, and $1800_{\circ}C$ being used with a $S_{i}O_{2}$ ratio of 3 wt%. The materials were sintered for 1 hour at $1760^{\circ}C,\;1780^{\circ}C$ and $1800^{\circ}C$ under a pressure of 20 MPa. The effects on sintering from the sintering system used, as well as from the composition of the sintering additives, were investigated by density measurements. Mechanical properties, such as flexural strength, were investigated to ensure the optimum conditions for a matrix of SiCf/SiC composites. Sintered densityand the flexural strength of fabricated LPS-SiC increased with an increase in sintering temperature. Particularly, the relative density of a sintered body at $1800^{\circ}C$ with a non-content of $S_{i}O_{2}$, a specimen of AYSO-1800, was 95%. Also, flexural strength was about 750MPa.

• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.89-100
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• 2007

In the companion paper, we provided the novel elastic-plastic constitutive model based on the micromechanics theory. Herein, the elastic and elastic-plastic deformation of granular soils is meticulously analyzed. To guarantee high accuracy of the microscopic parameter, the systematic procedure to evaluate the parameters is provided. The analysis of the elastic response during the isotropic and triaxial compression shows that the stress-level dependency of cross-anisotropic elastic moduli is induced by the power relationship of the contact force in the normal contact stiffness, while the evolution of fabric anisotropy is more pronounced during triaxial compression. The micromechanical analysis indicates that the plastic strains are likely to occur at very small strains. The plastic deformation of tangential contacts has an important role in the reduction of soil stiffness during axial loading.

• Korean Journal of Social Welfare
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• v.65 no.2
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• pp.255-285
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• 2013

The aim of this study is to demonstrate how Self-Sufficiency Promotion Centers (SSP Centers) run by social movement groups have struggled to defend their voluntary identities in conflict with SSP Centers operated by professional social welfare centers. Since political democratization, social movement groups have been increasing invited to run frontline public welfare agencies in South Korea, and Self-Sufficiency Program is one of the representative policies in which social movement groups have actively partaked. But many critical scholars have warned that such institutionalization of social movements into social welfare system is likely to dampen their voluntary nature and force them to render their hegemonic power to professional social welfare institutions. In contrast to the critical viewpoint, however, this study unveils how social movement-based SSP Centers have strived to tackle the professionalization pressure by deploying various survival strategies at the micro level. Through a historical discourse analysis on the frontline conflicts between social movement-based and social welfare-based SSP Centers, this study contends that social movement groups in Self-Sufficiency Program can still maintain their traditional spirit despite the obvious professionalization phenomenon.

• Journal of the korean Society of Automotive Engineers
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• v.9 no.3
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• pp.76-84
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• 1987

A study has been made to clarify the microstructural effect on static tensile properties of the dual phase steel, in which the martensitic phase encapsulated islands of ferritic phase. The main results are as follows: Yield strength is associated with the degree of plastic constraint factor and tensile strength increases with increasing of strain hardening exponent. Also, the variation of ductility is dependent upon the amount of micro-brittle facets.