SiO₂ 나노 콜로이드 량이 다른 Si₃N₄의 열처리에 따른 마모 특성

안석환,남기우,Ahn, Seok Hwan,Nam, Ki Woo 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.10

본 연구는 균열 치유 물질로 알려진 $SiO_2$ 나노 콜로이드의 첨가량을 달리한 $Si_3N_4$를 소결하여, 경면 연마한 시험편 표면에 $SiO_2$ 나노 콜로이드를 코팅하여 1273 K, 공기중에서 1시간 균열치유 처리하였다. 그 후, 마모시험편은 1073, 1273 및 1573 K에서 10분간 열처리하여 시험을 실시하였다. $SiO_2$ 나노 콜로이드를 코팅하여 열처리한 표면은 무코팅 표면보다 약간 거칠게 나타났으며, 열처리 온도에 따라 표면의 산화 정도는 조도와 뚜렷한 상관관계는 가지지 않았다. 그리고 마찰계수, 마모손실 및 굽힘강도는 표면 거칠기와 관계가 없었다. SKD11 상대재에 대하여 연삭마모의 거동을 보였으며, 마찰계수와 마모손실은 비례하였다. 또한, 강도가 클수록 마찰계수가 작고, 마모손실도 작았다. $SiO_2$ 나노 콜로이드 량의 증가에 따라서 마찰계수는 증가하다가 일정하게 되었지만, 마모손실은 증가하였다. 또한 열처리 온도가 증가함에 따라서 마찰계수는 약간 증가하는 경향을 나타내었다. This study sintered $Si_3N_4$ with different amounts of $SiO_2$ nano-colloid. The surface of a mirror-polished specimen was coated with $SiO_2$ nano-colloid, and cracks were healed when the specimen was treated at a temperature of 1273 K for 1 h in air. Wear specimen experiments were conducted after heat treatments for 10 min at 1073, 1273, and 1573 K. The heat-treated surface that was coated with the $SiO_2$ nano-colloid was slightly rougher than the noncoated surface. The oxidation state of the surface according to the heat treatment temperature showed no correlation with the surface roughness. Moreover, the friction coefficient, wear loss, and bending strength were not related to the surface roughness. $Si_3N_4$ exhibited an abrasive wear behavior when SKD11 was used as an opponent material. The friction coefficient was proportional to the wear loss, and the bending strength was inversely proportional to the friction coefficient and wear loss. The friction coefficient and wear loss increased with increasing amounts of the $SiO_2$ nanocolloid. In addition, the friction coefficient was slightly increased by increasing the heat treatment temperature.

크기가 다른 Shot에 의하여 Peening한 ZrO₂ 복합 세라믹스의 비커스 압입하중에 따른 와이블 통계 해석

안석환,김대식,남기우,Ahn, Seok Hwan,Kim, Dae Sik,Nam, Ki Woo 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.12

In this study, the effects of shot peening (SP) on the Vickers hardness of $ZrO_2$ were studied. The size of the shot balls were ${\phi}180{\mu}m$ and ${\phi}300{\mu}m$. The Vickers hardness was measured using an indentation load of 98 N and 294 N. The Vickers hardness was evaluated using Weibull statistical analysis. The scale parameters were significantly evident from the indentation load of 98 N and the shot ball of ${\phi}180 {\mu}m$. Generally, the shape parameters were also evident from the small short ball (180sp). Thus, it is shown that the introduction of a compressive residual stress by SP is an effective technique for increasing the mechanical properties of $ZrO_2$. 본 연구는 $ZrO_2$의 비커스 경도에 대한 쇼트 피닝 효과를 연구하였다. 쇼트의 크기는 ${\phi}180{\mu}m$와 ${\phi}300{\mu}m$를 사용하여 피닝하였다. 비커스경도는 압입하중 98 N과 294 N으로 측정하였다. 비커스 경도는 와이블 통계 해석을 수행하여, 볼 크기 및 압압 하중에 따르는 영향을 평가하였다. 척도 파라메터는 98 N 압입 하중 및 ${\phi}180{\mu}m$ 쇼트 볼에서 크게 나타났다. 형상 파라메터도 대체적으로 작은 쇼트 볼(180sp)이 크게 나타났다. 이것으로부터 SP처리에 의한 압축 잔류 응력은 $ZrO_2$의 기계적 성질의 향상에 좋은 방법이다.

탄소섬유를 이용한 Polyethylene배관의 전기융착 기술

안석환(Seok-Hwan Ahn),하유성(Yoo-Sung Ha),문창권(Chang-Kwon Moon) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.5

Fuel gas is an important energy source that is being increasingly used because of the convenience and clean energy provided. Natural gas is supplied to consumers safely through an underground gas pipe network made of a polyethylene material. In electrofusion, which is one of the joining methods used, copper wire is used as the heating wire. However, it takes a long time for fusion to occur because the electrical resistance of copper is low. In this study, therefore, electrofusion was conducted by replacing the copper heating wire with carbon fiber to reduce the fusion time and improve the production when joining large pipes. Fusion and tensile tests were performed after the electrofusion joint was made in the polyethylene pipe using carbon fiber. The results showed that the fusion time was shorter and the temperature inside the pipe was higher with and increase in the current value. The ultimate tensile strength of specimens was higher than that of virgin polyethylene pipe, except for polyethylene pipes joined using a current of 0.8 A. The best fusion current value was 0.9 or 1.0 A because of the short fusion time and lack of transformation inside the pipe. Thus, it was shown that carbon fiber can be used to replace the copper heating wire.

감육배관의 손상모드에 따른 음향방출 특성

안석환(SEOK-HWAN AHN),남기우(KI-WOO NAM),김선진(SEON-JIN KIM),김진환(JIN-HWAN KIM),김현수(HYUN-SOO KIM),박인덕(IN-DUCK PARK) 한국해양공학회 2002 韓國海洋工學會誌 Vol.16 No.5

Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. Acoustic emission(AE) has been widely used in various fields because of its extreme sensitivity, dynamic detection ability and location of growing defects. In this study, we investigated failure modes of locally wall thinned pipes and AE signals by bending test. From test results, we could be divided four types of failure modes of ovalization, crack initiation after ovalization, local buckling and crack initiation after local buckling. And fracture behaviors such as elastic region, yielding region, plastic deformation region and crack progress region could be evaluated by AE counts, accumulative counts and time-frequency analysis during bending test. The result of the frequency range is expected to be basic data that can inspect plants in real-time.

저속충격에 의한 복합재료 적층판의 손상

안석환(SEOK-HWAN AHN),김진욱(JIN-WOOK KIM),도재윤(JAE-YOON DO),김현수(HYUN-SOO KIM),남기우(KI-WOO NAM) 한국해양공학회 2005 韓國海洋工學會誌 Vol.19 No.1

The study investigated the nondestructive characteristics of damage, caused by low-velocity impact, on symmetric cross-ply laminates, composed of [0o/90o]16s, 24s, 32s, 48s. The thickness of the laminates was 2, 3, 4 and 6 ㎜, respectively. The impact machine used, Model 8250 Dynatup Instron, was a drop-weight type that employed gravity. The impact velocities used in this experiment were 0.75, 0.90, 1.05, 1.20 and 1.35 m/sec, respectively. Both the load and the deformation increased when the impact velocity was increased. Further, when the load increased with the laminate thickness in the same impact velocity, the deformation still decreased. The extensional velocity was quick, as the laminate thickness increased in the same impact velocity and the impact velocity increased in the same laminate thickness. In the ultrasonic scans, the damaged area represented a dimmed zone. This is due to the fact that the wave, after the partial reflection by the deflects, does not have enough energy to touch the opposite side or to come back from it. The damaged laminate areas differed, according to the laminate thickness and the impact velocity. The extensional velocities are lower in the 0o direction and higher in the 900 direction, when the size of the defect increases. However, it was difficult to draw any conclusion for the extensional velocities in the 45o direction.

크기가 다른 Shot에 의하여 Peening한 ZrO₂ 복합 세라믹스의 비커스 압입하중에 따른 와이블 통계 해석

안석환(Seok Hwan Ahn),김대식(Dae Sik Kim),남기우(Ki Woo Nam) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.12

본 연구는 ZrO₂의 비커스 경도에 대한 쇼트 피닝 효과를 연구하였다. 쇼트의 크기는 φ180 ㎛와 φ300 ㎛를 사용하여 피닝하였다. 비커스경도는 압입하중 98 N과 294 N으로 측정하였다. 비커스 경도는 와이블 통계 해석을 수행하여, 볼 크기 및 압압 하중에 따르는 영향을 평가하였다. 척도 파라메터는 98 N압입 하중 및 φ180 ㎛ 쇼트 볼에서 크게 나타났다. 형상 파라메터도 대체적으로 작은 쇼트 볼(180sp)이 크게 나타났다. 이것으로부터 SP처리에 의한 압축 잔류 응력은 ZrO₂의 기계적 성질의 향상에 좋은 방법이다. In this study, the effects of shot peening (SP) on the Vickers hardness of ZrO₂ were studied. The size of the shot balls were φ180 ㎛ and φ300 ㎛. The Vickers hardness was measured using an indentation load of 98 N and 294 N. The Vickers hardness was evaluated using Weibull statistical analysis. The scale parameters were significantly evident from the indentation load of 98 N and the shot ball of φ180 ㎛. Generally, the shape parameters were also evident from the small short ball (180sp) . Thus, it is shown that the introduction of a compressive residual stress by SP is an effective technique for increasing the mechanical properties of ZrO₂.

SiO₂ 나노 콜로이드 량이 다른 Si₃N₄의 열처리에 따른 마모 특성

안석환(Seok Hwan Ahn),남기우(Ki Woo Nam) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.10

본 연구는 균열 치유 물질로 알려진 SiO₂ 나노 콜로이드의 첨가량을 달리한 Si₃N₄를 소결하여, 경면 연마한 시험편 표면에 SiO₂ 나노 콜로이드를 코팅하여 1273 K, 공기중에서 1시간 균열치유 처리하였다. 그 후, 마모시험편은 1073, 1273 및 1573 K에서 10분간 열처리하여 시험을 실시하였다. SiO₂ 나노 콜로이드를 코팅하여 열처리한 표면은 무코팅 표면보다 약간 거칠게 나타났으며, 열처리 온도에 따라 표면의 산화 정도는 조도와 뚜렷한 상관관계는 가지지 않았다. 그리고 마찰계수, 마모손실 및 굽힘강도는 표면 거칠기와 관계가 없었다. SKD11 상대재에 대하여 연삭마모의 거동을 보였으며, 마찰계수와 마모손실은 비례하였다. 또한, 강도가 클수록 마찰계수가 작고, 마모손실도 작았다. SiO₂ 나노 콜로이드 량의 증가에 따라서 마찰계수는 증가하다가 일정하게 되었지만, 마모손실은 증가하였다. 또한 열처리 온도가 증가함에 따라서 마찰계수는 약간 증가하는 경향을 나타내었다. This study sintered Si₃N₄ with different amounts of SiO₂ nano-colloid. The surface of a mirror-polished specimen was coated with SiO₂ nano-colloid, and cracks were healed when the specimen was treated at a temperature of 1273 K for 1 h in air . Wear specimen experiments were conducted after heat treatments for 10 min at 1073, 1273, and 1573 K. The heat-treated surface that was coated with the SiO₂ nano-colloid was slightly rougher than the noncoated surface. The oxidation state of the surface according to the heat treatment temperature showed no correlation with the surface roughness. Moreover, the friction coefficient, wear loss, and bending strength were not related to the surface roughness. Si₃N₄ exhibited an abrasive wear behavior when SKD11 was used as an opponent material. The friction coefficient was proportional to the wear loss, and the bending strength was inversely proportional to the friction coefficient and wear loss. The friction coefficient and wear loss increased with increasing amounts of the SiO₂ nanocolloid. In addition, the friction coefficient was slightly increased by increasing the heat treatment temperature.

SiC<SUB>f</SUB>/SiC 복합재료의 굽힘 강도 특성 및 균열 치유 효과

안석환(Seok-Hwan Ahn),도재윤(Jae-Yoon Do),문창권(Chang-Kwon Moon),남기우(Ki-Woo Nam) 한국동력기계공학회 2013 동력시스템공학회지 Vol.17 No.4

용접열사이클 재현에 의한 SS400강 및 STS304강의 특성 평가

안석환(SEOK-HWAN AHN),정정환(JEONG-HWAN JEONG),남기우(KI-WOO NAM) 한국해양공학회 2005 韓國海洋工學會誌 Vol.19 No.6

The welding methods have been applied to the most structural products used in the automobile, ship construction, and construction. The structure steel must have sufficient strength of structure; however, the mechanical properties of the welded part changes when it is welded. Therefore, the stability or life of the structure may be affected by the changed mechanical properties. The mechanical properties of the welded part must be examined in order to ensure the safety of structure. In this research, the SS400 steel and the STS304 steel were used to estimate the mechanical properties of the HAZ by weld thermal cycle simulation. In this study, the materials were used to examine the weld thermal cycle simulation characteristic, under two conditions: the drawing with diameter of Φ10 and the residual stress removal treatment. To examine the mechanical properties by the weld thermal cycle simulation, the tensile test was carried out in room temperature. The crosshead speed was 1㎜/min.

FRP 선체구조용 접착제의 접착강도 평가

안석환(Seok-Hwan Ahn),최한규(Han-Kyu Choi),남기우(Ki-Woo Nam) 한국해양공학회 2010 韓國海洋工學會誌 Vol.24 No.1

Recently, the applied frequency of composite materials was increased from the viewpoint of lightweight, high strength and low cost when a leisure boat and a fishing boatwere built. However, studies on the mechanical properties of composite material with ship are rare. Specially, a leisure boat and fishing boat with FRP had been built by hand lay-up method. However, the vacuum infusion method is rising recently for ship building. The manufactured these FRP plates were combined by using the adhesive. Therefore, in this study Cleavage peel strength, Shear strength and fatigue limit of adhesive bonds by tensileloading were estimated. From test results, the strengths of FRP specimens made by the vacuum infusion method are higher than that of the hand lay-up method.