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.

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.

TiO₂/Epoxy 나노복합재의 발열 특성에 관한 연구

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

Recently, various nanoparticles have been used filler in polymer matrices. The particles of nano size are whether high or not cross-link density in polymer affects the thermal and mechanical properties of one. The properties change as a result of chemical reactions between the nanoparticles and the surface of the polymer. There are two models for nanocomposites: "repulsive interaction" and "attractive interaction" between the nanoparticles and matrix. In this study, the variation in the curing mechanism was examined when nano-size TiO₂ was dispersed into an epoxy (Bisphendol A, YD-128) with different curing agents. The results of this study showed that the exothermic temperature and Tg in the case of the nanoparticles used (Jeffamine) (D-180) at room temperature were reduced by an increase in the TiO₂ contents because of the "repulsive interaction" between the nanoparticles and the matrix. The tensile strengths were increased by increasing amounts of TiO₂ until 3 wt% because of a dispersion strengthening effect caused by the nanoparticles, because of the repulsive interaction. However, such tensile properties decreased at 5 wt% of TiO₂ because the TiO₂ was agglomerated in the epoxy. In contrast, in the case of the nanoparticles that used NMA and BDMA, the exothermic temperature and Tg tended to rise with increasing amounts of TiO₂ as a result of the "attractive interaction". This was because the same amounts of TiO₂ were well dispersed in the epoxy. The tensile strength decreased with an increase in the TiO₂ contents. In the general attractive interaction model, however, the cross-link density was higher, and tensile strength tended to increase. Therefore, for the nanoparticles that used NMA, it was difficult to conclude that the result was caused by the "attractive model."

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.

용접열사이클 재현에 의한 SS400강 및 ST5304강의 특성 평가

안석환(SEOK-HWAN AHN),최문오(MOON-OH CHOI),김성광(SUNG-KWANG KIM),손창석(CHANG-SEOK SON),남기우(KI-WOO NAM) 한국해양공학회 2007 韓國海洋工學會誌 Vol.21 No.5

The welding methods have been applied in the most structural products from multi-field of automobile, ship construction and construction, and so on. The structure steel must have enough strength of structure. In this study, SS400 steel and STS304 steel were used to estimate the corrosion characteristics of the weld thermal cycle simulated HAZ. To evaluate the corrosion characteristics, also, the materials with two conditions were used in 3.5% NaCl. The one is to the drawing with diameter of Φ10 and the other is to the residual stress removal treatment. The electrochemical polarization test and immersion test were carried out. from test results, corrosion potential, corrosion current density, weight loss ratio and corrosion rate were measured. In the kinds of SS400 steels, corrosion potential of weld thermal cycle simulated specimens after the heat treatment showed somewhat the direction of noble potential. And in the base metal to be drawing weight loss ratio and corrosion rate occurred higher than the other kinds. In the kinds of STS304 steels, the result of base metal to be drawing was similar to results of SS400 steels, too. Two kinds of 750 ℃ and 1300 ℃ of weld thermal cycle simulation after the heat treatment were rather higher than the other kinds in weight loss ratio and corrosion rate.

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.

원주방향 미관통 표면결함을 가지는 탄소강 배관의 두께관 통전,후의 피로거동 평가

안석환 ( Seok Hwan Ahn ) 한국어업기술학회 2000 수산해양기술연구 Vol.36 No.2

수분환경에서 탄소섬유강화 에폭시수지의 내구성에 대한 나노입자의 영향

안석환(Seok-Hwan Ahn),최영민(Young-Min Choi),문창권(Chang-Kwon Moon) 한국동력기계공학회 2014 동력시스템공학회지 Vol.18 No.2

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.