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구병춘(B. C. Goo),전우수(W. S. Jeon) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
A WEB-based code has a far-reaching influence. Nearly everywhere in the world, one may browse on the INTERNET and use WEB-based codes. In this context, we have been developing a WEB-based code for fatigue life prediction of metals and welded joints. The developed code could be served on the INTERNET domestically and internationally for engineers, students, and researchers. The C and C++ program languages were used. It is very easy to use the code because it is operated on graphical user interface (GUI). It seems to contribute a little to fatigue research, industrial development, and education, etc. It could also help fatigue-related people predict fatigue life prediction.
구병춘(B. C. Goo) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Weight reduction of vehicle components is one of the important concerns. Carbon/carbon-SiC composites have been studied as candidates for light brake discs. A preform was produced by hot pressing a mixture of resin and carbon-fibers. After pyrolyzing the preform, liquid Si infiltration was performed to obtain a C/C-SiC brake disc. For this test product, thermal analysis by finite element method was carried out, and thermal characteristics were analyzed. It was found that the thermal stress was under the tensile strength of the material and depended on the parameters used for the finite element model.
구병춘(B. C. Goo),이찬우(C. W. Lee),권태수(T. S Kwon) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4
용접구조물은 대부분 용접 토우에서 균열이 발생하여 성장하고 어느 크기에 도달하여 구조물이 작용하중을 더는 지탱하지 못하게 되면 파손에 이르게 된다. 용접부의 용접금속과 모재의 열영향부가 만나는 부위는 용접열에 의해 미세조직이 변하고 용접 비드의 표면에 요철이 생겨 응력집중이 발생하기 쉽고, 표면층에는 용접으로 인장 잔류응력이 작용하므로 피로강도 측면에서 매우 취약하다. 용접부의 피로강도를 향상하기 위해 용접 토우 주위를 고주파 가진 액추에이터를 진동시켜 충격 핀이 용접 토우 부위를 타격하면 소성변형이 발생하여 인장 잔류응력이 압축 잔류응력으로 변한다. 그리고 피닝은 조직을 미세하게 하고, 거친 표면을 매끄럽게 하여 응력집중을 완화해 피로강도를 향상한다. 본 연구에서는 독자적으로 초음파 피닝 장비를 개발하고, SM490A 강판으로 용접시편을 제작하고 개발 장비로 용접 토우에 피닝을 하여 피닝이 용접부의 피로수명에 미치는 영향을 평가하였다. Most cracks in the weld structure occur and grow on the weld toe, reaching a certain size, resulting in breakage if the structure no longer supports the working load. The area where weld metal and parent metal meet each other is very weak in terms of fatigue strength due to microstructural change and tensile residual stress. To improve the fatigue strength of the weld joint, ultrasonic impact peening is widely used. Peening makes the microstructure fine, smoothes the rough surface, and relieves stress concentration. In this study, we developed ultrasonic peening equipment, manufactured welded specimens with SM490A steel plate, and investigated the effect of ultrasonic impact peening on the fatigue lifetime of the welded specimens.
집중 유도 전위차법을 이용한 철도차량 차축 결함 탐상의 유한요소 해석
구병춘(B. C. Goo),임충환(C. H. Lim),권석진 (S. J. Kwon) 한국정밀공학회 2005 한국정밀공학회 학술발표대회 논문집 Vol.2005 No.10월
The NDT(Non-Destructive Testing) is valid for the defect detection of rolling stocks because it can be used to detect defects in invisible places. For example, in case of wheelsets fatigue cracks are initiated in the wheel seat that suffers from fretting fatigue damage. But the conventional ICFPD method can not be applied to detect such cracks in press-fit area of the axle by some technical problems. In this study, we introduced a new ICFPD (Induced Current Focusing Potential Drop) method that can be applied in press-fit area of the axle. And we performed the finite element analysis of the new ICFPD method using measured electromagnetic properties of the wheel and axle. It seems that our approach is very useful for the detection of defects in invisible places.
철도차량용 CV 흑연 주철 제동디스크 개발 및 피로특성 평가
구병춘(B. C. Goo),임충환(C. H. Lim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Thermal fatigue in brake discs may cause serious accidents, deterioration of brake performance and increase of maintenance costs due to frequent exchange of friction materials. One of the methods to improve resistance to thermal shock is to use compacted vermicular graphite. In this study, three candidate materials with different components were chosen and cast into specimens. Main components of the cast irons are Fe, C, Si, Mn, Ni, Cr, and Cu. Mechanical properties, chemical compositions, crystallographic structures and graphite types of the cast specimens were analyzed. Then fatigue tests were carried out by a rotary bending fatigue tester. S-N curves of the developed compacted vermicular cast irons were compared with that of a conventional disc material. In addition, thermal fatigue tests were performed. The thermal and mechanical fatigue test results were compared. It is found the developed materials have a higher fatigue strength than the disc material in service.
구병춘(B. C. Goo),정현승(H. S. Jung) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
Aluminum alloy composites with SiC particles are useful for weight reduction of mechanical components. But they are expensive and it is difficult to make complex components. If we found out a reliable method to join aluminum alloys and Al/SiC composites, we could make complex mechanical parts at a low price. In this study A356 aluminum alloy and A356/SiC 20 vol.% composite were chosen as dissimilar materials. To join two different materials by casting, first, A356 blocks were cast and cylindrical holes with conical end were drilled in the blocks. A mold with a cylindrical hole was placed on an A356 cast block. Molten A356/SiC at about 750℃ was poured into the mold. Before pouring molten A356/SiC, A356 blocks were heated and kept at 550℃. Using the specimens tensile strength tests were carried out. As tensile forces increased, some composite bars were pulled out from the A395 blocks and others fractured near the border. Tensile strengths depended on the surface conditions of the cast-bonded joints.
SM490A와 SS400의 대기부식 및 피로강도의 실험적 연구
구병춘(B. C. Goo) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
For structural design and diagnosis, quantitative relationship between corrosive degradation and variation of mechanical properties such as tensile strength and fatigue strength is needed. But it is difficult to find data associated with corrosive degradation of structural structures. In this study, first of all we established the atmospheric corrosion test procedure. And using specimens of SM490A and SS400 on the atmospheric corrosion test bed, we carried out tensile and fatigue tests at regular intervals. And we studied the effect of post-weld heat treatment on the tensile and fatigue behaviour. It is found fatigue strength decreases as the atmospheric corrosion period increases.