크롬 프리 친환경 유/무기 하이브리드 코팅액에 의한 냉연강판의 내식특성

남기우(Ki Woo Nam),김정량(Jung Ryang Kim),최창민(Chang Min Choi) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.2

In the past, a very popular method for reducing the corrosion on zinc involved the use of chemical conversion layer coatings based on Cr<SUP>+6</SUP>. However, there is an important problem with using chromium salts as a result of restrictive environmental protection legislation. This study investigated the optimum condition for galvanized steel using an organic/inorganic solution with a Ti composition. In the case of a fixed heat treatment time, the corrosion resistance values of LR-0727(1) and LR-0727(2) were improved as the heat treatment temperature increased, and the optimum minimum temperature decreased with the heat treatment time. At the optimum heat treatment condition of two coating solutions, the heat treatment time of the LR-0727(1) solution was shorter than LR-0727(2) for the same heat treatment temperature. LR-0727(1) coated specimens did not show desquamation, and all of the specimens showed a good adhesive property. In contrast, in the case of the LR-0727(2) coated specimens, desquamation arose. Therefore, the adhesive property of LR-0727(1) was superior to that of LR-0727(2). The pencil hardness had a 3H average for all of the coating solutions and heat treatment conditions. In the case of a corrosion resistance test with boiling water, the coated specimens of LR-0727(1) were discolored, but LR-0727(2) was not. Finally, LR-0727(1) was more moisture proof than LR-0727(2).

인장 굽힘피로를 받는 부재의 피로수명과 균열관통

남기우(Ki-Woo Nam) 한국해양공학회 1994 韓國海洋工學會誌 Vol.8 No.1

The leak-before-break(LBB) design on the large structures such as ship's hull, tank structure, pressure vessels etc. is one of the most important subjects for the evaluation and the assurance of safety. In these structures, various loads are acting. In some structural members, therefore, out-of-plane stress due to bending often may become with in-plane stress due to stretching. In the present report, the characteristics of fatigue life and penetration behaviour from a surface cracked plate under combined tension and bending have been studied experimentally and analytically by using eccentricity. Estimation of fatigue crack growth was done with the Newman-Raju formula before penetration, and with the stress intensity factor after penetration proposed by the author. Calculated aspect ratio showed the good agreement with the experimental result. It was also found that particular crack growth behaviour and crack shape after penetration can be satisfactorily evaluated using the K solution proposed.

레이저 피닝한 STS304의 특이한 피로 특성 평가

남기우(Ki-Woo Nam),팽재은(Jae-Eun Paeng),구경희(Kyoung-Hee Gu),손대진(Dai-Jin Son) 한국동력기계공학회 2021 동력시스템공학회지 Vol.25 No.3

균열 길이와 코팅방법에 따른 Si₃N₄의 균열 치유 특성

남기우(Ki Woo Nam),문창권(Chang Kwon Moon),박상현(Sang Hyun Park),은경기(Kyung Ki Eun),김종순(Jong Soon Kim) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.11

본 연구에서는 장균열을 가지는 Si₃N₄ 세라믹스의 균열 길이와 코팅 방법에 따르는 균열 치유 특성을 규명하였다. 약 100 ~ 500 ㎛의 균열 길이는 24.5 ~ 98 N의 하중을 사용하여 비커스 압자를 이용하여 만들었다. 24.5 N의 하중으로 만든 단균열의 경우, SiO₂ 나노 콜로이드 코팅된 균열재는 모재보다 약 140 % 증가한 가장 높은 굽힘 강도를 보였지만, 장균열은 모재보다 낮은 굽힘 강도를 나타내었다. 그러나 대부분의 장균열 시험편의 굽힘 강도는 균열재보다 약간 증가하였다. 이러한 결과에 따라서, 복수 압입에 의한 Si₃N₄ 세라믹스의 균열 치유 특성을 코팅방법에 따라 연구하였다. 장균열 시험편의 가장 효과적인 코팅 방법은 정수압코팅방법이었다. In this study, we analyzed the crack-healing characteristics of specimens; different crack lengths and coating methods of Si₃N₄ ceramic structures with long cracks were analyzed. Cracks with lengths of about 100-500 μm were obtained using a Vickers indenter for a load of 24.5-98 N. In the case of a crack obtained by applying a load of 24.5 N, the crack-healed specimen with SiO₂ nanocolloid coating exhibited the highest bending strength, which was higher than that of a smooth specimen by 140%, but the bending strength of a crack-healed specimen that had a SiO₂ nanocolloid coating and originally had multiple cracks was lower than that of a smooth specimen. However, when compared to the cracked specimens, the bending strength of most specimens with multiple cracks increased slightly. On the basis of these results, the crack-healing characteristics of Si₃N₄ ceramic structures with multiple indentations were studied for different coating methods. The most effective coating method for long-crack specimens was hydrostatic pressure coating.

고강도 사이알론의 균열치유와 고온강도 특성

남기우(Ki Woo Nam),박상현(Sang Hyun Park),박승원(Seung Won Park),문석재(Suk Jae Moon) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.9

Sialon was produced by hot-pressing the mixtures of Si₃N₄, AlN and Y₂O₃ powders. All fracture tests were performed on a three-point loading system with a 30 ㎜ bending span. Fracture toughness and Vickers hardness of smooth specimen were average 7.05 ㎫ m<SUP>0.5</SUP> and Hv = 1580, respectively. Density of three kinds of specimens, smooth specimen, smooth and healed specimen, smooth with SiO₂ colloidal coating and healed specimen, had beyond 99 % of theoretical density. Bending strength of smooth healed specimens had high strength more than 1 ㎬. Crack healed specimens recovered as strength as smooth specimen. That is, cracked specimen with SiO₂ colloidal coating on cracked part recovered strength by heat treatment, completely. Crack healing of Si₃N₄ composite ceramics had contributed glassy SiO₂ to strength recovery. Limiting high temperature for bending strength of heat treated smooth specimen for bending strength was about 1273 K.

〈학술논문 or 기술논문〉 균열 길이에 따른 Si3N4의 균열치유 특성

남기우(Ki Woo Nam),박상현(Sang Hyun Park),이희방(Hee Bang Lee) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

This study analyzed the crack-healing characteristic of Si₃N₄ composite ceramics according to the crack lengths. Cracks of about 100 - 300 ㎛ lengths were obtained from a Vickers indenter using the load of 24.5 98 N. In case of crack using a load of 24.5 N, the crack-healed specimen with SiO₂ nano colloidal coating exhibited the highest bending strength, which is increased about 140 % than that of smooth specimen. But, the multi-crack-healed specimens with SiO₂ nano colloidal coating were lower than that of smooth specimen. However, the bending strength of most multi-crack specimens slightly increased than that of the cracked specimens.

센터필라 적용을 위한 이종 접합강의 충격 특성 해석에 관한 연구

남기우(Ki Woo Nam),박상현(Sang Hyun Park),유정수(Jung Su Yoo),이상문(Sang Mun Lee) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.8

본 연구에서는 레이저 TWB로 용접된 이종재료의 동적 특성에 대한 해석이 수행되었다. 해석프로그램은 Hyper works 10.0으로 Solver는 LS-DYNA v.971, 모델링 요소는 2D-Shell, 요소 수는 35,641개, 노드 수는 36,561개이다. 충격속도는 10 ㎞/h이다. 상ㆍ하부의 용접선 높이에 따르는 영향을 연구하기 위하여, 하부의 길이를 300 ㎜와 400 ㎜로 하였다. 얻어진 결론은 다음과 같다. 길이 300 ㎜인 하부 재료 SPFC980의 변형은 가장 작고, 충돌 흡수 에너지는 가장 크다. 하부 냉연강 기준으로 TWB의 위치가 짧을수록 성능이 우수하게 나타났다. 즉, 상대적으로 상부 고강도강인 SABC1470 재료가 차지하는 비율에 따라 성능이 좌우되었다. 하부 재료 SPFH590은 큰 변형이 나타났고, 충돌성능은 SPFC980보다 현저히 떨어졌다. 따라서 충돌 성능 해석 결과에서 하부 재료 SPFC980인 길이 300 ㎜가 가장 우수한 것으로 나타났다. This study was carried out to analyze the dynamic characteristics of laser tailor-welded blanks (TWBs) made of dissimilar materials. The analysis was performed using Hyper Works 10.0 with Solver LS-DYNA v.971. 2D-Shell was used as the modeling element, and the number of elements and nodes was 35,641 and 36,561, respectively. The impact speed was 10 ㎞/h. To analyze the impact characteristics according to the height of the weld line for the upper and lower parts of the center pillar, the length of the lower part was set as 300 and 400 ㎜. When the lower part was made of SPFC980 steel with a length of 300 ㎜, the deformation was the smallest and the absorbed energy of the impact force was the largest. On based the lower part of center pillar, the position of TWB shows the shorter and the better value. In other words, the performance depended on the proportion of the upper part made of high-strength SABC1470 steel. A lower part made of SPFH590 steel showed large deformation. In contrast, a lower part made of SPFC980 steel showed significantly lesser deformation. Therefore, the impact performance of a lower part made of SPFC980 steel with a length of 300 ㎜ showed the best analysis result.

압연 온도와 압연량이 다른 STS202의 탄성파 특성

남기우(Ki-Woo Nam),전현(Hyun Jeon),이기식(Ki-Sik Lee),탁영준(Young-Joon Tak) 한국동력기계공학회 2021 동력시스템공학회지 Vol.25 No.3

Fe-27Mn-4Co-2Al 합금의 감쇠능에 미치는 Si의 영향

남기우(Ki-Woo Nam),김범수(Beum-Su Kim),최병철(Byoung-Chul Choi) 한국동력기계공학회 2021 동력시스템공학회지 Vol.25 No.2

873∼1173 K에서 열처리된 강화흑연강(Compacted Graphite Iron, CGI)의 음향방출 특성

남기우(Ki-Woo Nam),안병건(Byung-Kun Ahn),이수철(Soo-Chul Lee) 한국비파괴검사학회 2013 한국비파괴검사학회지 Vol.33 No.5

CGI는 주철보다 큰 강도 또는 작은 무게가 요구되는 응용에서 인기를 얻고 있다. 최근, 강화흑연강은 디젤 엔진 블록, 터보 하우징 및 배기 매니폴드에 사용된다. 이 논문은 873~1173 K에서 1~24 시간 동안 열화된 CGI340의 기계적 성질의 변화에 따른 음향방출 특성을 평가하였다. 연필심 파괴시험 결과에서, 탁월주파수 및 모재의 속도는 각각 97 kHz와 5,490 m/s이었다. 인장시험에서 모재는 상대적으로 높은 탁월주파수를 얻었다. 그러나 열처리된 재료, 열처리 시간이 길고, 열처리 온도가 높을수록, 낮은 주파수의 영역에서 얻어졌다. 이러한 현상은 장기간의 사용에 의해 나타난다. CGI is gaining popularity in applications that require either greater strength, or lower weight than cast iron. Recently, compacted graphite iron has been used for diesel engine blocks, turbo housings and exhaust manifolds. This paper were assessed acoustic emission characteristics according to the mechanical properties change of degraded CGI340 during 1-24 hours at 873~1173 K. In results of pencil lead fracture test, the dominant frequency and the velocity of base metal were 97 kHz and 5490 m/sec, respectively. The base metal in a tensile test was obtained relatively high dominant frequency. However, the heat treated materials, the longer the heat treatment time, the higher the heat treatment temperature, were obtained in the area of lower frequencies. This phenomenon appears by long-term use.