• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.5
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• pp.513-521
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• 2012

The aim of this study was to determine the brittle fracture behavior of reactor pressure vessel steel by considering the temperature dependence of a damage model. A multi-island genetic algorithm was linked to a Weibull stress model, which is the model typically used for brittle fracture evaluation, to improve the calibration procedure. The improved calibration procedure and fracture toughness test data for SA508 carbon steel at the temperatures $-60^{\circ}C$, $-80^{\circ}C$, and $-100^{\circ}C$ were used to decide the damage parameters required for the brittle fracture evaluation. The model was found to show temperature dependence, similar to the case of NUREG/CR-6930. Finally, on the basis of the quantification of the difference between 2- and 3-parameter Weibull stress models, an engineering equation that can help obtain more realistic fracture behavior by using the simpler 2-parameter Weibull stress model was proposed.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.104-104
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• 2003

다양한 구조를 갖는 polysilsesquioxane은 열적, 전기적, 기계적 성질이 우수하여 차세대 고집적 반도체용 저 유전율 층간 절연막 재료로 부각되고 있으며, 유/무기 하이브리드 재료로 많은 연구 대상이 되고 있다. 그러나 PMSSQ(polymethylsilsesquioxane)는 취성으로 인한 반도체 제조의 CMP 공정에서 미세 크렉 발생의 위험이 있으므로 막의 인성 강화가 요구되고 있다. 이를 위하여 PMSSQ의 취성을 보완하기 위한 목적으로 선형 분자인 dimethylsiloxane을 10-20mo1% 도입하고자 하였다. 이때 도입된 dimethylsiloxane기가 PMSSQ에 균일하게 분포하지 않으면 실리콘 기판에 코팅 후 약 43$0^{\circ}C$의 열처리 공정 중에 열분해 되는 위험이 있다. 이에 따라 본 연구에서는 dimethylsiloxane기의 열분해에 의한 문제를 최소화하기 위하여 출발 물질인 MTMS(methyltrimethoxysilane)와 DMDMS(dimethyldimethoxysilane)과의 가수분해 속도차이를 고려한 단계(step) 반응법과 MTMS 와 DMDES(dimethyldiethoxysilane)를 사용한 리간드 교환법(ligand exchange)으로 dimethylsiloxane이 PMSSQ에 도입된 공중합체를 합성하였다. 각 합성 방법에 따라 합성된 공중합 PMSSQ의 특성을 TGA, TG-IR, $^1$H-NMR, $^{29}$ Si-NMR과 in-situ IR을 통하여 분석하였다. 또한 dimethylsiloxane 도입 양 및 상기 제조 방법에 따라 합성한 공중합체를 Si 기판위에 코팅하여 43$0^{\circ}C$에서 열처리한 후 코팅막의 강도, 두께 및 굴절율 변화를 ellipsometry 와 nanoindenter로 분석하였다.

• Korean Journal of Materials Research
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• v.1 no.3
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• pp.145-150
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• 1991

Crystallization and embrittlement of $Fe_{78}B_{13}Si_{9}$ amorphous alloy was investigated by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. The crystallization comprizes two exothermic processes. In the first crystallization stage, $\alpha$-(Fe, Si) dendrites are formed from the amorphous state, and in the second crystallization, $Fe_2B$ compounds are formed. An abrupt decrease of the fracture strain of the ribbon started from amorphous started annealed at about $340^{\circ}C$

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.250-258
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• 2000

The reinforcing effects of ductile short-fiber reinforced brittle matrix composites are studied by, measuring flexural strength, fracture toughness and impact energy as functions of fiber volume fraction and length. The parameters of fracture mechanics, K and J are applied to assess fracture toughness and bridging stress. It is found that fracture toughness is greatly, influenced by the bridging stress ill which fiber pull-out is occur. For the reinforcing effects as functions of fiber volume fraction($V_f$ = 1, 2, 3 %) and length(L = 3, 6. 10cm), the flexural strength is maximum at $V_f$ = 1% and both fracture toughness.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1101-1104
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• 2001

The special purposed materials, such as ceramics and stainless steel, are widely used in the various industrial area. They have properties of the higher strength of material, the wear-resistance, and the corrosion proof. But ceramics is a difficult-to-grind material which possesses the higher level of a strength and a brittleness. In this study, the theoretical investigation of a grinding force and of a surface roughness was conducted. The evaluations of grinding characteristics on the hardened-brittle and difficult-to-grind materials were experimentally carried out.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.724-728
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• 1996

The instrumented Charpy impact test is generally used to evaluate the dynamic fracture toughness for varying engineering materials. However, the test is known to be difficult to evaluate the dynamic fracture toughness for very brittle materials because of the small crack initiation load. To evaluate the dynamic fracture toughness of verybrittle materials, it is necessary to develop a load sensitive instrumented tup. In this study, a polymer tup, which has small Young's modulus, is used for the instrumented Charpyimpact test and a proper testing method is developed. The results show that the developed method can measure rapidly changing loads from the moment of contact between the tup and the specimen to dynamic crack initation of the very brittle materials.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.6
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• pp.724-730
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• 2006

Fracture behavior of brittle solids is closely related to microcracking. A meso-scale analysis method using the natural element method is proposed for the analysis of brittle microcracking solids. The microcracking is assumed to occur along Voronoi edges in the Voronoi diagram generated using the nodal points as the generators. The mechanical effect of microcracks is considered by controlling the material constants in the neighborhood of the microcracks. The meso-analysis method is applied to the simulation of the microcracking behaviors of brittle solids subjected to tensile macrostress. The method is also applied to the analysis of the propagation of a macrocrack accompanied by the coalescence with microcracks formed near the macrocrack-tip.

• Tribology and Lubricants
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• v.8 no.2
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• pp.35-43
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• 1992

취성재료의 마멸천이기구를 규명하기 위해 반무한탄성체상에 표면균열이 존재할 때 그 위를 헤르쯔 접촉하중이 이동할 경우를 해석모델로 하여 선형파괴역할을 도입하여 해석하였다. 해석방법으로는 표면균열을 인상전위의 연속분포로 치환하여 Erdogan-Gupta의 방법으로 균열끝면의 응력확대계수를 구하여, 취성재료의 균열전파조건인 Erdogan-Sih Criterion을 사용하여 그 전파특성을 해석하였다. 본 논문에서는 마멸율이 적은 마멸에서 마멸율이 큰 마멸로 전이할 때 급격한 표면손상과 마찰계수의 급격한 증가를 동반하므로 이에 대한 해석에 중점을 두었다. 해석결과는 접촉하중과 마찰계수의 증가는 표면균열의 전파를 야기시켜 대규모 마멸입자를 생성시키게 됨을 보여주었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.271-271
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• 2003

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.3
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• pp.309-316
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• 2015

A state-based peridynamic model is able to describe a general constitutive model from the standard continuum theory. The response of a material at a point is dependent on the deformation of all bonds connected to the point within the nonlocal horizon region. Therefore, the state-based peridynamic model permits both the volume and shear changes of the material which is promising to reproduce the complicated dynamic brittle fracture phenomena, such as crack branching, secondary cracks, cascade cracks, crack coalescence, etc. In this paper, the two-dimensional state-based peridynamic model for a linear elastic plane stress solid is employed. The damage model incorporates the energy release rate and the peridynamic energy potential. For brittle glass materials, the impact of the crack-parallel compressive stress waves on the crack branching pattern is investigated. The peridynamic solution for this problem captures the main features, observed experimentally, of dynamic crack propagation and branching. Cascade cracks under strong tensile loading and secondary cracks are also well reproduced with the state-based peridynamic simulations.