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        • SCOPUSKCI등재

          초기 연신율법을 이용한 크리프 수명예측 평가

          공유식,임만배,이상필,윤한기,오세규,Kong, Yu-Sik,Lim, Man-Bae,Lee, Sang-Pill,Yoon, Han-Ki,Oh, Sae-Kyoo 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.6

          The high temperature creep behavior of heat machine systems such as aircraft engines, boilers and turbines in power plants and nuclear reactor components have been considered as an important and needful fact. There are considerable research results available for the design of high temperature tube materials in power plants. However, few studies on the Initial Strain Method (ISM) capable of securing repair, maintenance, cost loss and life loss have been made. In this method, 3 long time prediction Of high temperature creep characteristics can be dramatically induced through a short time experiment. The purpose of present study is to investigate the high temperature creep lift of Udimet 720, SCM 440-STD61 and 1Cr-0.5Mo steel using the ISM. The creep test was performed at 40$0^{\circ}C$ to $700^{\circ}C$ under a pure loading. In the prediction of creep life for each materials, the equation of ISM was superior of Larson-Miller Parameter(LMP). Especially, the long time prediction of creep life was identified to improve the reliability.

        • 자동차 캠축용 마찰용접재의 회전굽힘피로 특성

          공유식(Yu-Sik Kong),김선진(Seon-Jin Kim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

          A study on dissimilar friction welded joints were performed using 20 mm diameter solid bar in forging steel(SF 45) to carbon steel(SM 45C) for automobile cam shaft applications. The optimal friction welding parameters were selected to ensure reliable quality welds on the basis of visual examination, tensile test, hardness measurement, rotary bending fatigue test(RBFT) and microstructural investigation. So, this paper deals with optimizing the welding conditions and analyzing various RBFT properties about heat-treated BM, as-welded and PWHT. The results of the mechanical tests are described when the optimal welding condition is n=2,000 rpm, P1=70 MPa, P2=140 MPa, t1=7 sec, t2=5 sec. Fatigue limit of BM(SF45) and PWHT for the RBFT were investigated 180, 250 MPa, respectively.

        • KCI등재

          해양차량 경량화용 마그네슘합금의 마찰용접 및 AE 특성

          공유식(Yu-Sik Kong),이진경(Jin-Kyung Lee),강대민(Dae-Min Kang) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.6

          In this paper, friction welded joints were constrncted to investigate the mechnnical praperties of welded 15-㎜ diameter solid bars of Mg alloy (AZ31B). The main friction welding parameters were selected to endure reliable quality welds on the basis of visual examination, tensile tests, impact energy test, Vickers hardness surveys of the bonds in the area and heat affected zone (HAZ), and macrostructure investigations. The study reached the following conclusions. The tensile strength of the friction welded nmterials (271 ㎫) was increased to about 100 % of the AZ31B base metal (274 ㎫) under the condition of a heating time of 1 s. The metal loss increased lineally with an increase in the heating time. The following aptimal friction welding conditions were determined: rotating speed (n) = 2000 rpm, heating pressure (HP) = 35 ㎫, upsetting pressure (UP) = 70 ㎫, heating time (HT) = 1 s, and upsetting time (UT) = 5 s, for a metal loss (Mo) of 10.2 ㎜. The hardness distribution of the base metal (BM) showed HV55. All of the BM parts showed levels of hardness that were approximately similar to friction welded materials. The weld interface of the friction welded parts was strongly mixed, which showed a well-combined structure of macro-particles without particle growth or any defects. In addition, an acoustic emission (AE) technique was applied to derive the aptimum condition for friction welding the Mg alloy nondestructively. The AE count and energy parameters were useful for evaluating the relationship between the tensile strength and AE parameters based on the friction welding conditions.

        • KCI등재

          컴프레서 체결용 볼트의 적정 토크 설정에 관한 연구

          공유식(Yu Sik Kong),김태완(Tae Wan Kim) 한국트라이볼로지학회 2013 한국윤활학회지(윤활학회지) Vol.29 No.5

          When a threaded fastener is tightened, the torque-tension relationship is highly sensitive to two friction components: thread friction and head friction. In this study, we carried out friction experiments and analyses to determine the optimum clamping torque setting for bolt joints. First, we measured the coefficients of thread friction and head friction under the same running conditions of the bolt clamping process for lubricated and nonlubricated bolts. We also measured axial tension through bolt clamping tests using lubricated and non-lubricated bolts attached to a strain gauge. Finally, we compared the experiment and theoretical results.

        • KCI등재

          굴삭기용 호스 니플의 마찰용접과 음향방출기법의 적용

          공유식(Yu-Sik Kong),이진경(Jin-Kyung Lee) 한국비파괴검사학회 2013 한국비파괴검사학회지 Vol.33 No.5

          마찰용접은 축 대칭 단면금속을 용접하는 매우 유용한 결합 과정이다. 본 논문에서는 굴삭기용 호스니플의 관대관 마찰용접을 시행하여 수송산업 등에 적용 가능성을 제안하고 마찰용접 변수의 기계적 특성을 분석하여 최적화 조건을 결정하고자 하였다. 회전속도, 마찰가열압력 및 가열시간 등 주요 변수를 선정하고 각 매개변수의 세 가지 수준에서 실험을 수행하였다. 한편, 최적의 마찰용접조건을 비파괴적으로 도출하기 위하여 음향방출기법이 적용되었으며 카운터, 이벤트 및 파형과 주파수 스팩트럼 등의 AE 파라미터들을 이용하여 마찰용접시 발생하는 신호를 분석하고자 하였다. 인장시험 결과 최적의 용접 변수는 회전속도 1300 rpm, 마찰가열압력 15 MPa, 마찰가열시간 10초로 나타났으며, 이벤트는 마찰용접된 시험편의 인장강도를 추정하는데 유용한 파라미터가 되었다. Friction welding is a very useful joining process to weld metals which have axially symmetric cross section. In this paper, the feasibility of industry application was determined by analyzing the mechanical properties of weld region for a specimen of tube-to-tube shape for excavator hose nipple with friction welding, and optimized welding variables were suggested. In order to accomplish this object, friction heating pressure and friction heating time were selected as the major process variables and the experiment was performed in three levels of each parameter. An acoustic emission(AE) technique was applied to evaluate the optimal friction welding conditions nondestructively. AE parameters of accumulative count and event were analyzed in terms of generating trend of AE signals across the full range of friction weld. The typical waveform and frequency spectrum of AE signals which is generated by friction weld were discussed. From this study the optimal welding variables could be suggested as rotating speed of 1300 rpm, friction heating pressure of 15 MPa, and friction heating time of 10 sec. AE event was a useful parameter to estimate the tensile strength of tube-to tube specimen with friction weld.

        • KCI등재

          수송차량 안전벨트용 모터축재의 마찰용접 최적화(1)

          공유식(Yu-Sik Kong),안석환(Seok-Hwan Ahn) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.1

          Dissimilar friction welds were produced using 15-mm diameter solid bars of chrome molybdenum steel (KS SCM440) and carbon steel (KS SM20C) to investigate their mechanical properties. The main friction welding parameters were selected to ensure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond area and HAZ, and macro-structure investigations. The specimens were tested as-welded and post-weld heat treated (PWHT). The tensile strength of the friction welded steel bars was increased to 100% of the SM20C base metal under the condition of a heating time of more than four seconds. Optimal welding conditions were n = 2,000 (rpm), HP = 60 (MPa), UP = 100 (MPa), HT = 5 (s),and UT = 5 (s), when the total upset length was 7.8 (mm). The hardness distribution peak of the friction welded joints could be eliminated using PWHT. The two different kinds of materials were strongly mixed to show a well-combined structure of macro-particles, with no molten material, particle growth, or defects.

        • KCI등재

          SF45와 SM45C의 마찰용접 최적화에 따른 회전굽힘피로 특성

          공유식(Yu Sik Kong),박영환(Young Whan Park) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.3

          본 연구는 수송기계 축 등에 이용되는 캠 형상 부분만을 기존의 단조품인 SF45와 축 부분은 일반기계구조용 탄소강재인 SM45C를 직경 20 mm를 이용하여 이종 마찰용접을 수행하였다. 최적조건을 규명하기 위해 인장시험 등 용접품질과의 상관관계를 고찰하였고, 또한 최적조건에서 마찰용접 후 열처리를 시행하여 용접재(As-welded)와 후열처리재(PWHT)에 대한 회전굽힘 피로시험을 시행하였다. 결과적으로 두 이종재가 강한 혼합으로 계면에서도 개재물 및 산화막이 플래시로 토출되어 양호한 접합상태임을 확인하였다. 더욱이 모재(SF45)와 후열처리재의 피로한도 각각 180 MPa, 250 MPa로 나타났다. 이는 후열처리재가 SF45 모재에 비해 약 40 %의 피로수명이 향상되었음을 확인하였다. A study on dissimilar friction-welded joints was performed for cam shaft applications using solid bar samples, 20mm in diameter, of forging steel(SF45) and carbon steel(SM45C). The main parameters of friction welding such as tensile tests, Vickers hardness surveys of the bond of area, the heat affected zone (HAZ), and the observation of microstructure were investigated to ensure a good quality of friction welding through visual observations. The specimens were tested as-welded and post weld heat treatment(PWHT). This paper deals with optimizing the welding conditions and analyzing various rotary bending fatigue test(RBFT) properties about heat-treated base metal(BM), as-welded and PWHT. Consequently, two materials for friction welding are strongly mixed with a well-combined structure of micro-particles without any molten material, particle growth, or any defect. Moreover, the fatigue limit of BM(SF45) and PWHT for the RBFT were observed as 180MPa and 250MPa, respectively. It was confirmed that the PWHT causes approximately 40% improvement in the fatigue limit when compared to the BM(SF45).

        • KCI등재

          상어 표피 모사 리블렛 구조의 젖음성 평가

          공유식(Yu Sik Kong),김태완(Tae Wan Kim) 한국트라이볼로지학회 2013 한국윤활학회지(윤활학회지) Vol.29 No.5

          Shark skin has functionalities such as self-cleaning and antifouling; it also exhibits excellent drag reduction owing to a hierarchical structure of microgrooves and nanometer-long chain mucus drag reduction interfaces around the shark body. In this study, the wettability of a shark skin surface and its replicas are evaluated. First, a shark skin template is taken from a real shark. Then, shark skin replicas are produced directly from a shark skin template, using a micromolding technique. The quantitative replication precision of the shark skin replicas is evaluated by comparing the geometry of the shark skin template to the replica using 2D surface profiles. Contact angles at the solid-air-water interfaces are evaluated for the shark skin template and its replicas under two conditions: with and without hydrophobic coating. The results show that the microriblets on shark skin improve the hydrophobic feature and play a critical role in self-cleaning.

        • KCI등재

          자동차 후진기어용 축재(SM 45C-SF 45)의 이종마찰용접 특성

          공유식(Yu-Sik Kong),윤성필(Seong-Pil Yoon),김선진(Seon-Jin Kim) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.1

          자동차 후진기어용 축재는 단조재로서 그 형상은 복잡하고 열처리 및 가공공정이 어려울 뿐 아니라, 제품수명 저하 등의 문제점으로 인한 경제적 손실이 크다. 따라서 종전의 일체형 단조품을 캠 형상 부분만을 기존의 단조품(SF 45)으로 사용하고, 나머지 축 부분은 일반 기계구조용 탄소강재(SM 45C)로 대체를 위한 이종마찰용접을 적용하였다. 마찰용접 변수인 회전수, 마찰압력, 업셋압력, 가열시간, 업셋시간 등의 상호작용에 의한 용접품질과의 상관관계를 고찰하였으며, 최적조건에서 마찰용접을 한 후 용접재(as-welded)와 고주파 열처리를 시행한 후열처리재(PWHT)의 접합부 특성을 비교 고찰하였다. 이는 종전의 일체형 단조품에 비해 단조비용 절감, 피로수명향상, 기계가공에 따른 공정수 및 재료절감 등의 경제적 파급효과가 클 것으로 기대된다. Friction welding is a common practice to join axially symmetrical parts for automobile industry applications. The shaft for automobile reverse idle gear is generally produced by forging steel, SF 45. This method is not so good because of high cost of material and production. In this study, in order to investigate the possibility of application of SM 45C to SF 45 dissimilar friction welding, the dissimilar friction welded joints were performed using 20 mm diameter solid bar in forging steel(SF 45) to carbon steel(SM 45C). The optimal friction welding parameters were selected to ensure reliable quality welds on the basis of visual examination, tensile test, micro-Virkers hardness surveys of the bond of area and optical microstructure investigations for welded joint parts. Finally, post weld heat treatment(PWHT) of the high-frequency induction hardening was performed for the friction welded specimens under the optimal welding conditions. And then, the mechanical properties were compared for as-welded and PWHT in SM 45C to SF 45.

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