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곽시영(Si-Young Kwak),김학구(Hak-Ku Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.4
내부결함은 주조제품의 강도 및 피로 수명에 있어 상당한 영향을 미치기 때문에 주조공정에서 주요 관심사 이다. 일반적으로 내부결함은 응력집중을 발생시키며 균열의 시작점일 수 있다. 그러므로 피로 수명과 같은 기계적 거동에 있어 수축공과 같은 결함을 이해하는 것이 중요하다. 본 논문에서는 내부결함을 고려한 인장시편에 대해 피로시험을 수행하고 주조결함을 고려할 때의 피로노치계수를 산정하였다. 실제 내부결함은 산업용 CT 장비를 통해서 확인하였으며 확인된 결함은 형상단수화법에 의해 단순화 하고 응력해석과 피로해석을 수행하였다. 그 결과 우리가 제안한 방법이 기계적 거동에 있어 내부결함의 영향을 조사하고 피로수명 등을 예측함에 있어 유용함을 확인할 수 있었다. Internal defects (Shrinkage, blow hole, etc.) are a m에 or concern in casting process because it significantly influence on strength and fatigue life of casting products. In general, it causes stress concentration and can be a starting point of cracks. Therefore, it is important to understand the effects of shrinkage on mechanical performance such as fatigue life. In this study, we performed fatigue experiment for tensile specimens with internal shrinkage defects. Real shrinkage defect in casting was scanned by industrial CT(Computerized Tomography), and subsequently it’s shape was simplified by ellipsoidal primitives for the structural and fatigue analysis(SSM, Shape Simplification Method). The analysis results were compared with the results by real experimental with internal defects. It turned out that it is possible to consider real shrinkage of casting in stress and fatigue analysis and the proposed method give us a tool to predict fatigue life of casting and to investigate the effects of shrinkage defects on mechanical performance.
내부 결함을 포함하는 알루미늄 합금 주조품의 피로해석을 위한 모델링
곽시영 ( Si Young Kwak ),황호영 ( Ho Young Hwang ),김학구 ( Hak Ku Kim ),이성원 ( Sung Won Lee ) 한국주조공학회 2010 한국주조공학회지 Vol.30 No.5
The structural stress and fatigue behavior of tensile specimen containing internal shrinkage defect were modeled. Real shrinkage defect in casting was scanned by industrial CT (computed tomography), and subsequently its shape was simplified by ellipsoidal primitives for the structural analysis (S.S.M., shape simplification method). The analysis results were compared with the results by real shrinkage shape without any simplification process. It was possible to consider real shrinkage of casting in stress analysis and the method to predict fatigue life of casting with defect was proposed.
주조품의 피로수명 예측을 위한 내부결함 모델링 및 해석적 접근
곽시영,김학구 (사)한국CDE학회 2012 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2012 No.2
In the casting process, It is possible to minimize shrinkage and blowhole by working on modifying casting system, but to remove them completely is impossible. So the parts are exposed to working load. It is traditional to assume completely soundness in initial state of casting part which is excluding shrinkage and blowhole in manufacturing process. So design engineers apply sufficient safety factor because of possibility of unexpected performances of cast products. It would lead to a lot of error during fatigue life analysis. In this paper, we studied on prediction method of fatigue life of cast product containing shrinkage by using CT and SSM and conduct static and fatigue analysis. After analysis, experiments were conducted with specimens that have widespread porosities and predicted fatigue life used by strain-life and lefm method. Subsequently fatigue life from computational simulation and predicted life by theory compared with experiments results. Through this study, we can predict fatigue life of casting product by SSM(shape simplication method)
내부 결함을 고려한 주조 제품의 피로수명 예측을 위한 결함 형상단순화 해석모델
곽시영(Si-Young Kwak),김학구(Hak-Ku Kim) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.10
내부결함은 주조제품의 강도 및 피로 수명에 있어 상당한 영향을 미치기 때문에 주조공정에서 주요 관심사 이다. 일반적으로 내부결함은 응력집중을 발생시키며 균열의 시작점이 되므로 피로 수명과 같은 기계적 거동에 있어 수축공과 같은 결함을 이해하는 것이 중요하다. 본 논문에서는 내부결함을 고려한 인장시편에 대해 피로시험을 수행하고 주조결함을 고려할 때의 특정하중피로노치 계수를 산정하였다. 실제 내부결함은 산업용 CT 장비를 통해서 확인하였으며 확인된 결함은 형상단순화법에 의해 타원체로 단순화 하고 응력해석과 피로해석을 수행하였다. 그 결과 우리가 제안한 방법이 기계적 거동에 있어 내부결함의 영향을 조사하고 피로수명 등을 예측함에 있어 유용함을 확인할 수 있었다. Internal defects are a major concern in the casting process because they have a significant influence on the strength and fatigue life of casting products. In general, they cause stress concentration and can be a starting point of cracks. Therefore, it is important to understand the effects of internal defects on mechanical properties such as fatigue life. In this study, fatigue experiments on tensile specimens with internal defects were performed. The internal defects in the casting product were scanned by an industrial CT scanner, and its shape was simplified by ellipsoidal primitives for the structural and fatigue analysis. The analysis results were compared with experimental results for casting products with internal defects. It was demonstrated that it is possible to consider internal defects of casting products in stress and fatigue analysis. The proposed method provides a tool for the prediction of the fatigue life of casting products and the investigation of the effects of internal defects on mechanical performance.
이청산,곽학구,박경재,장환,Lee, Cheong-San,Kwak, Hak-Koo,Park, Kyung-Jae,Jang, Hwan 한국동물위생학회 1998 韓國家畜衛生學會誌 Vol.21 No.1
This study was carried out to investigate the prevalence of antibody against Toxoplasma gondii in the dog by Latex agglutination test and Indirect fluorescent antibody test. Two month-old dogs were infected intraperitoneally with T gondii to observe histopathological and immunohisto-chemical changes. Results obtained through this experiment were summarized as follows ; 1. Among the serum samples of 163 heads of the dog, 10 samples(6.1%) were positive. 2. In the sex, 6 heads (7.1%) out of 84 female dogs and 4 heads(5.1%) out of 79 male dogs were positive. However, there were no significant differences between the male and female. 3. Overall proportion of agreement between indirect fluorescent antibody and Latex agglutination test in 163 sera of dogs was 97.5%. 4. When 2 month-old dogs were infected intraperitoneally with T gondii, main clinical signs were intermittent fever, dyspnea, diarrhea. In general, the infected dogs recovered closely on the 11th day of post-inoculation. 5. At necropsy, petechial and ecchymotic hemorrages and swelling in small intestine, lung, spleen, liver and kidney were observed. 6. In histopathological observation, interstitial pneumonia, hyperemia and hemorrhages in lung were observed. Focal necrosis of hepatocytes, the neutrophil and basophil in the renal tubular epithelium were observed. 7. By immunohistochemical staining using Vectorstain ABC kit, the positive cells were recognized in the lung and the liver. 8. By indirect fluorescent antibody test, the Toxoplasma antibodies in the infected dogs were detected on the 15th day of postinoculation.