• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4647-4658
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• 2023

In this paper, elastic-plastic fracture mechanics analysis is performed to determine the critical crack sizes of the multipurpose canister (MPC) manufactured using austenitic stainless steel under dynamic loading conditions that simulate drop accidents. Firstly, dynamic finite element (FE) analysis is performed using Abaqus v.2018 with the KORAD (Korea Radioactive Waste Agency)-21 model under two drop accident conditions. Through the FE analysis, critical locations and through-thickness stress distributions in the MPC are identified, where the maximum plastic strain occurs during impact loadings. Then, the evaluation using the failure assessment diagram (FAD) is performed by postulating an external surface crack at the critical location to determine the critical crack depth. It is found that, for the drop cases considered in this paper, the principal failure mechanism for the circumferential surface crack is found to be the plastic collapse due to dominant high bending axial stress in the thickness. For axial cracks, the plastic collapse is also the dominant failure mechanism due to high membrane hoop stress, followed by the ductile tearing analysis. When incorporating the strain rate effect on yield strength and fracture toughness, the critical crack depth increases from 10 to 20%.

• 한국기계가공학회지
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• 제15권3호
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• pp.130-134
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• 2016

Due to the need for advanced technologies in the automotive industry, the demand for lighter and safer vehicles has increased. Even though various nonferrous metals, like Aluminum, Magnesium and also Carbon Fiber Reinforced Plastic (CFRP), have been implemented in the automotive industry, a lot of technical research and development is still focused on ferrous metals. In particular, the market volume of High Strength Steel (HSS) parts and Ultra High Strength Steel (UHSS) by hot press forming parts has expanded significantly in all countries' automotive industries. A new tool steel, High Thermal-Conductivity Tool Steel (HTCS), for stamping punches and dies has been developed and introduced by Rovalma Company (Spain), and it is able to support better productivity and quality during hot press forming. The HTCS punches and dies could help to reduce cycle time due to their high thermal conductivity, one of the major factors in hot press forming operation. In this study, test dies were manufactured in order to verify the high thermal conductivity of HTCS material compared to SKD6. In addition, thermal deformation was inspected after the heating and cooling process of hot press forming. After heating and cooling, the test dies were measured by a 3D scanner and compared with the original geometry. The results showed that the thermal deformation and distortion were very small even though the cooling time was reduced by 2 seconds.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.58.1-58.1
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• 2011

WC-Co and other similar cemented carbides have been widely used as hard materials in industrial cutting tools and as mould metals; and a number of techniques have been applied to improve its microstructural characteristics, hardness and ear resistance. Cobalt is used primarily to facilitate liquid phase sintering and acts as a matrix, i.e. a cementing phase between WC grains. A uniform distribution of metal phase in a ceramic is beneficial for improved mechanical properties of the composite. WC-Co, starting from initial powders, is vastly used for a variety of machining, cutting, drilling, and other applications because of its unique combination of high strength, high hardness, high toughness, and moderate modulus of elasticity, especially with fine grained WC and finely distributed cobalt. In this study, that started with two different compositions of initial powders, WC-7.5wt%Co and WC-12wt%Co with initial powder size being 1~3 ${\mu}m$, magnetic pulsed compaction followed by subsequent vacuum sintering were carried out to produce consolidated preforms. Magnetic Pulsed Compaction (MPC), a very short duration (~600 ${\mu}s$), high pressure (~4 Gpa), high-density preform molding method was used with varied pressure between 0.5 and 3.0 Gpa, in order to reach an initial high density that would help improve the sintering behavior. For both compositions and varied MPC pressure, before and after sintering, changes in microstructural behavior and mechanical properties were analyzed. With proper combination of MPC pressure and sintering, samples were obtained with better mechanical properties, densification and microstructural behavior, and considerably improved than other conventional processes.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2007년도 추계 학술논문 발표대회
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• pp.71-74
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• 2007

With the changes of times the building materials tend to extend the demand for application under the special environment. Since high-ductile mortar is developed, the building materials show excellent performance like toughness, compression, tensile, and bending, etc. in the general concrete from the existing brittle point. And, recently they are widely used as repairing and reinforcing materials both at home and abroad because they are recognized as excellence like durability and fire-resistance. However, it is in a situation of creating problems in durability because it frequently happened deterioration of buildings that have already repaired and reinforced at a time when it requires reconstruction of recently deteriorated construction structure recently. Therefore, in this study improved with a more repair Material development and reinforcement of the second high-ductile mortar products for a variety of basic materials were presented want, research plans used include traditional repair materials and the newly developed PCM (polymer cement mortar) structural reinforcement type indicated that comparison. PCM analysis in order to present a rate depending on the types fiber 0, 1.2 and 2.0(%) at three levels and mixture water according to ratios of weight to Plain in the 2.0 and 1.85(kg) at two levels is set, the results were as follows. 1) This study has shown that PCM had excellent strain hardening behavior at the same time that the bending stress increased according to the fiber contents. 2) This study has shown that it had the durability performance due to the high substance transmission according to the fiber contents.

• 대한금속재료학회지
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• 제49권8호
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• pp.614-618
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• 2011

Nanopowders of MgO, $Al_2O_3$ and $SiO_2$ were made by high energy ball milling. The rapid sintering of nanostructured $MgAl_2O_4-Mg_2SiO_4$ composites was investigated by a high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. Highly dense nanostructured $MgAl_2O_4-Mg_2SiO_4$ composites were produced with simultaneous application of 80MPa pressure and induced output current of total power capacity (15 kW) within 2min. The sintering behavior, gain size and mechanical properties of $MgAl_2O_4-Mg_2SiO_4$ composites were investigated.

• 산업융합연구
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• 제22권1호
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• pp.105-115
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• 2024

본 연구는 학생 태권도 겨루기 선수들의 정신력이 태권도 겨루기 경기력에 미치는 영향을 분석하고자 실시하였다. 연구 대상은 대한태권도협회에 태권도 겨루기 선수로 등록이 되어 있는 중학교, 고등학교, 대학교 343명을 대상으로 편의표집 방법을 사용하였으며, 전문가 회의를 통해 Loehr가 제작한 Mental Toughness Test 검사도구를 사용하였다. 자료분석은 일반적 특성에 따른 정신력의 하위요인별 수준을 분석하기 위하여 t-test, 일원배치분산을 실시하였고, 집단 간 다중비교를 위하여 Schéffe test를 통해 사후검증을 실시하였다. 정신력의 하위요인별 수준과 경기력을 분석하기 위하여 상관분석 및 다중회귀분석을 실시하였다. 연구결과 태권도 겨루기 학생 선수들의 일반적 특성인 성별과 연령에 따른 정신력 차이에서 정신력 관련 하위요인 중 자신감, 각성 수준 조절, 시각화 및 심상조절, 동기 수준, 긍정적 에너지, 태도 조절은 성별과 연령에서 유의한 차이가 나타났고, 인지된 경기력에서는 연령과 운동 경력에서 유의한 차이가 나타나 결과적으로 태권도 겨루기 학생 선수들의 경우 심리적 훈련 이외에 연령과 다양한 경험이 정신력과 관련 하위요소에 긍정적인 영향을 미치는 것으로 나타났다. 따라서 태권도 겨루기 학생 선수들 중 특히 중학교 고등학교 시기에는 다양한 시합의 경험과 훈련 시 심리적을 동반하여 시합에서의 결과적인 자신 평가에 대한 두려움을 이겨낼 수 있도록 지도와 훈련이 제공되어야 하겠다.

• Composites Research
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• 제27권4호
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• pp.123-129
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• 2014

세라믹 기지 복합재료는 세라믹 기지에 고 용융 온도, 낮은 밀도, 고 탄성과 강도를 가진 탄화물, 질화물, 보론화물, 산화물 등의 강화재료를 끼워 넣어 파괴 인성을 높인 것이다. 이들 소재는 우주 비행체의 열 차폐 시스템, 또 고온의 가스 터빈의 연소실, 터빈 블레이드, 고정자(Stator) 베인 등의 부품에 사용되며, 버너와 화염 유지기(Flame holder), 고온 가스 덕트에는 산화 CMC가 사용되고 있고, 극심한 열 충격이 일어나는 브레이크 디스크나 시스템의 부품, 그리고 슬라이드 베어링 부품에도 활용되고 있다. 이러한 CMC에 대한 연구 개발은 미국의 우주 비행체 활용 목적을 비롯하여, 미국, 일본, 유럽에서의 초고속항공기와 가스 터빈용, 그리고 핵 융합용 등의 목적으로 국방과 에너지 산업과 같은 전략적 분야의 활용을 목표로 개발되고 있다.

• 한국강구조학회 논문집
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• 제18권3호
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• pp.395-403
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• 2006

최근 건설되는 강교량은 지간의 장대화 및 교량으로서의 기능은 물론이고 외적 조형미, 유지관리, 공사기간과 수명주기 비용 등을고려한 구조적 단순함을 요한다. 이러한 요구를 충족시키기 위해 극후판이나 TMCP 강과 같은 고성능 강의 사용이 요구된다. TMCP (Thermo-Mechanical Control Proces)법에 의해 제조되는 TMCP 강은 탄소당량이 적고, 조직이 미세하며, 강도 및 인성이 좋다. 최근에는 인장강도 60MPa급의 고강도 TMCP 강인 SM570-TMC 강이 개발되어 토목구조물에 일부 적용되고 있으며, 점차 그 영역을 확장하려는 추세에 있다. 하지만 이러한 고강도 TMCP 강을 강구조물에 적용하기 위해서는 그 재료적 특성뿐만 아니라 용접 시 발생하는 접합부의 역학적 특징을 명확히 할 필요가 있다. 따라서 본 연구에서는 고온인장실험을 통해서 SM570-TMC 강의 고온시의 기 계적 특성을 조사하였고, 이를 잔류응력 특징을 명확히 하였다.

• 한국분말재료학회지
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• 제19권2호
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• pp.117-121
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• 2012

Tool steels serve a large range of applications including hot and cold workings of metals and injection mouldings of plastics or light alloys. The high speed steels (HSS) are specifically used as cutting tools and wear parts because it has high strength, wear resistance and hardness along with appreciable toughness and fatigue resistance. From the view of HSS microstructure, it can be described as metallic matrix composites formed by a ferrous with a dispersion of hard and wear resistant carbides. The experimental specimens were manufactured using the PIM with T42 powders (50~80 vol.%) and polymer (20~50 vol.%). The green parts were debinded in n-hexane solution at $60^{\circ}C$ for 8 hours and thermal debinded at an $N_2-H_2$ mixed gas atmosphere for 8 hours. Specimens were sintered in high vacuum ($10^{-5}$ Torr) and various temperatures.

• International Journal of Safety
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• 제6권2호
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• pp.1-7
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• 2007

In this study mechanical strength of A53B carbon steel was analyzed using several types of test specimens directly machined from oil recycling pipe experienced a failure due to hydrogen attack in chemical plants. High temperature hydrogen attack (HTHA) is the damage process of grain boundary facets due to a chemical reaction of carbides with hydrogen, thus forming cavities with high pressure methane gas. Driven by the methane gas pressure, the cavities grow on grain boundaries forming intergranular micro cracks. Microscopic optical examination, tensile test, Charpy impact test, hardness measurement, and small punch (SP) test were performed. Carbon content of the hydrogen attacked specimens was dramatically reduced compared with that of standard specification of A53B. Traces of decarburization and micro-cracks were observed by optical and scanning electron microscopy. Charpy impact energy in hydrogen attacked part of the pipe exhibited very low values due to the decarburization and micro fissure formation by HTHA, on the other hand, data tested from the sound part of the pipe showed high and scattered impact energy. Maximum reaction forces and ductility in SP test were decreased at hydrogen attacked part of the pipe compared with sound part of the pipe. Finite element analyses for SP test were performed to estimate tensile properties for untested part of the pipe in tensile test. And fracture toughness was calculated using an equivalent strain concept with SP test and finite element analysis results.