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유효응력 (有效應力) 과 전위 구조로 해석한 70Cu-30Ni 합금의 Creep 변형 기구
홍준화,남수우 대한금속재료학회(대한금속학회) 1980 대한금속·재료학회지 Vol.18 No.5
온도범위 0.44∼0.64T_m과 응력범위 15∼336㎫의 실험조건하에서 70Cu-30Ni 고용체 합금의 creep 변형기구를 규명하는 연구로서 변형기구의 정확한 원인을 확인하기 위하여 유효응력을 측정하여 다음과 같은 온도에 무관한 creep 변형 속도방정식을 얻었다. ε˙_s=1.84×10^(-4)(σ^*/σ_(0.05))^(2.6) 여기서 σ^*와 σ_(0.05)는 각각 유효응력과 0.05연신하의 항복응력을 뜻한다. 실험을 통하여 얻어진 자료를 분석한 결과 상기의 합금이 실험조건하에서의 변형기구는 jog을 포함하는 나사전위의 jog 부분의 비보존적 운동에 의해서 지배받는 것으로 결론 지어진다. The steady state creep deformation mechanism of 70Cu-30Ni solid solution alloy was investigated for the temperature range of 0.44∼0.64T_m. For the better understanding of the mechanism the effective stress was measured and the creep rate was expressed with the effective stress as ε˙_s=1.84×10^(-4)(σ^*/σ_(0.05))^(2.6) where σ^* and σ_(0.05) are the effective stress and 0.05 strain offset proof stress, respectively. The observed experimental results indicate that the creep deformation mechanism of the given alloy under the stress range of 15∼336㎫ is controlled by the non-conservative motion of the jogged screw dislocations.
Mn-Mo-Ni 저합금강의 취성균열 전파에 미치는 입계 결정방위차의 영향
홍준화,오용준,김민철 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.5
The effect of orientation relationship between two adjacent grains on the brittle crack propagation was systematically investigated in the viewpoint of misorientation at the boundaries using Electron Back-Scatter Diffraction(EBSD) technique. Crystallographic orientation around the path of secondary crack under the fracture surface has been observed with fractured 3 point band specimen at -100℃. Use of EBSD technique allows the crystallographic cracking plane of the material to be inferred. For every crack observed, the trace of the plane was perpendicular to a $lt;001$gt; direction of the cracked packet. The concept of the geometric compatibility factor has been introduced in order to explain and predict the crack propagation between two adjacent grains. This factor can be calculated from the measuring the two angles from {001} pole figure. A possible cracking plane predicted from calculation of a geometric compatibility factor was coincident with those found in observation.
원자력발전소 주요부품 구조재료의 파괴 저항성 및 건전성
홍준화 대한기계학회 1995 大韓機械學會誌 Vol.35 No.6
원자로 압력용기 및 주 배관등 원자력발전소 주요부품 구조재료에서의 파괴저항성 및 건전성 문제를 일부 시험결과 및 평가결과와 함께 살펴보았다. 원자력환경하에서는 중성자 조사에 의한 조사취화 및 고온에서의 장기간 유지에 따른 열취ㅘ로 재료 고유의 파괴저항치가 가동에 따라 매우 감소하고, 이에 따라 부품의 건전성 및 수명이 매우 위협받고 있음을 확인하였다. 현재 가동중인 원자로 10기, 건설중인 8기, 합계 18기로 세계 9위의 원자력발전국이 되며, 대북 경수로 지원과 세계시장 진출을 계획하고 있는 우리나라에서는, 보다 안전한 원자력발전소가 건설되기 위해서, 재료의 균질성 및 파괴인성 개선연구, 조사특성 연구 등을 통해 파괴저항성이 우수한 국산소재를 제작\ulcorner공급하도록 하여야 한다. 또한, 수명기간 동안 고도의 건전성을 유지하면서 운전하고, 나아가 수명연장 운전을 위해서는, 용기 등 주요 부품의 상태(파괴인성치, 결함, 작용 응력)를 정확히 진단, 예측, 평가하여야 하고, 이들이 건전성에 미치는 영향평가와 건전성평가기술 확립을 통한 수명예측기술을 확보하여야 한다(이들은 대부분 파괴역학 시험 침 해석기술에 바 탕을 두고 있다). 국내 산\ulcorner학\ulcorner연 관련자들의 특별한 관심을 촉구하는 바이다.
GDF15 Is a Novel Biomarker for Impaired Fasting Glucose
홍준화,정효균,박혜윤,정경혜,이주희,정진규,김군순,김현진,구본정,송민호 대한당뇨병학회 2014 Diabetes and Metabolism Journal Vol.38 No.6
Background: Growth differentiation factor-15 (GDF15) is a protein that belongs to the transforming growth factor β superfamily. An elevated serum level of GDF15 was found to be associated with type 2 diabetes mellitus (T2DM). T2DM is an inflammatory disease that progresses from normal glucose tolerance (NGT) to impaired fasting glucose (IFG). Hence, we aimed to validate the relationship between GDF15 and IFG. Methods: The participants were divided into the following three groups: NGT (n=137), IFG (n=29), and T2DM (n=75). The controls and T2DM outpatients visited the hospital for routine health check-ups. We used fasting blood glucose to detect IFG in nondiabetic patients. We checked the body mass index (BMI), C-reactive protein level, metabolic parameters, and fasting serum GDF15 level. Results: Age, BMI, triglyceride, insulin, glucose, homeostatic model assessment-insulin resistance (HOMA-IR), and GDF15 levels were elevated in the IFG and T2DM groups compared to the NGT group. In the correlation analysis between metabolic parameters and GDF15, age and HOMA-IR had a significant positive correlation with GDF15 levels. GDF15 significantly discriminated between IFG and NGT, independent of age, BMI, and HOMA-IR. The serum levels of GDF15 were more elevated in men than in women. As a biomarker for IFG based on the receiver operating characteristic curve analysis, the cutoff value of GDF15 was 510 pg/mL in males and 400 pg/mL in females. Conclusion: GDF15 had a positive correlation with IR independent of age and BMI, and the serum level of GDF15 was increased in the IFG and T2DM groups. GDF15 may be a novel biomarker for detecting IFG in nondiabetic patients.
Type 316L 스테인리스가의 입계 석출 및 예민화에 미치는 질소의 영향
홍준화,류우석,오용준 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.8
Nitrogen effect on sensitization behavior of type 316L stainless steel was investigated in view of thermal precipitation. The investigated alloys had a variation in carbon and nitrogen contents. The sensitization resistance was improved with decreasing of carbon content and increasing of nitrogen content. From a microstructural observation on the sensitized alloys, it was found that the addition of nitrogen up to 0.15% increased sensitization resistance through suppressing the initiation and growth of M_(23)C_6 type carbide. M_6C type carbide was only formed at the alloy with medium nitrogen content. Besides carbides, Mo-rich precipitates such as intermetallic η and χ phases, and five-fold symmetry phase were observed at the grain boundary. These phases were more popular in the medium nitrogen alloy than in low nitrogen alloy at the same aging condition. From a TEM-EDS(energy despersive spectroscope) analysis, it was found that these Mo-rich phases had not a significant deterimental effect on the sensitization resistance.