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고속분기기 노스가동크로싱의 성능 및 유지보수 효율화를 위한 개량 방안에 관한 연구
윤병현(Byung-Hyun Yoon),황광하(Kwang-Ha Hwang),나호필(Ho-Pil Na),박광련(Kwang-Ryun Park),김만철(Man-Cheol Kim) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.10
고속철도에서 차량의 방향을 전환시키는 고속분기기는 궤도용품 중에서 가장 중요한 핵심 기술로 분류된다. 고속분기기는 F18.5번 이상이 해당되며 국내에는 F18.5, F26, F46이 주로 사용되고 있다. 수량은 고속1단계(서울~대구)에 91틀, 고속2단계(대구~부산) 37틀, 호남고속(오송~광주) 48틀이 사용되어 총 176여틀이 현장에 적용되어 있다. 2004년 개통한 고속1단계 자갈도상용의 경우 사용기간이 10여년이 경과함에따라 부품별 교체 주기가 도래하고 있고 이에따른 유지보수력이 증가하고 있는 실정이다. 노스가동크로싱은 약 90여가지의 부품으로 조합된 가장 복잡한 구조로써 이의 유지보수에는 많은 시간과 전문기술 인력이 필요한 실정이다. 이에 성능을 향상시키면서 유지보수가 간편한 노스가동 크로싱 구조의 개발에 관한 연구를 수행하였다. A study on the performance improvement of the high speed turnout’s movable nose crossing and maintenance efficiency. the high speed turnout that converts the direction of the rolling stock is classified as the most important core technology out of all railway products. F18.5 and above are applied to the high speed turnout, and F26 and F46 are mainly used domestically. For quantity, 100 sets are applied to high speed line phase 1(Seoul~Daegu), 45 sets are each applied to phase 2(Daegu~Busan) and Ho-nam high speed line (OSong~GwangJu), which means that a total of approximately 190 sets are being applied on site. In case of the ballast track of high speed line phase 1 which opened in 2004, the exchange period for each component has arrived as its use of term has passed 10 years and accordingly, the maintenance for it is on the increase. the movable nose crossing has a very complex structure as it is combined with approximately 90 components, so a lot of time and manpower would be required. Therefore, we performed a study on the improvement of the movable nose crossing structure for simple maintenance by enhancing its performance.
Local compression에 의한 CTOD 시편내의 용접잔류응력 재분포
주성민,윤병현,장웅성,방한서,방희선,노찬승,Joo, Sung-Min,Yoon, Byung-Hyun,Chang, Woong-Seong,Bang, Han-Sur,Bang, Hee-Seon,Ro, Chan-Seung 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.6
When conducting CTOD test, especially in thick welded steel plate, fatigue pre-cracking occasionally failed to satisfy the requirements of standards thus making the test result invalid. Internally accumulated residual stress of test piece has been thought as one of the main reasons. The propagation of fatigue crack, started from the tip of machined notch, which might have propagated irregularly due to residual stress field. To overcome this kind of difficulty three methods to modify the residual stress are suggested in standard i.e. local compression, reverse bending and stepwise high-R ratio method. In this paper not only multi pass welding but also local pre-compressing process of thick steel plate has been simulated using finite element method for clarifying variation of internal welding residual stress. The simulated results show that welding residual stress is compressive in the middle section of the model and it is predominantly increased after machining the specimen. Comparing as-welded state all component of the welding residual stress changing to compressive in the tip of machine notch whereas residual stress of the outer area remain as tensile condition relatively. Analysis results also show that this irregular residual stress distribution is improved to be more uniformly by applying local compression.
800 MPa급 고강도강 용접금속의 미세조직 특성 비교 연구
이재희,김상훈,윤병현,김환태,길상철,이창희,Lee, Jae-Hee,Kim, Sang-Hoon,Yoon, Byung-Hyun,Kim, Hwan-Tae,Kil, Sang-Cheol,Lee, Chang-Hee 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.1
Microstructural characteristics of two high strength (600 MPa & 800 MPa) weld metals produced by flux-cored arc welding process (FCAW) were evaluated. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at relatively high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 85% acicular ferrite and 15% low temperature forming phases (bainite, martensite). The prior austenite grain size of 800 MPa grade weld metal was decreased by solute drag force. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by a transmission electron microscopy (TEM). In both 600 MPa and 800MPa grade weld metals, the inclusions were mainly consisted of Ti-oxide and Mn-oxide, and the average size of inclusions was $0.7{\mu}m$. The 800 MPa grade weld metal exhibited higher tensile strength and similar toughness compared with the 600 MPa grade weld metal. This result is mainly due to a higher fraction of low temperature products and a lower fraction of grain boundary ferrite in the 800 MPa grade weld metal.
합금강관의 Energy Resistance Welding 용접조건에 따른 미세조직 거동 및 기계적 특성 연구
이경민,이동언,김성웅,윤병현,강희재,강남현,조경목,Lee, Kyung-Min,Lee, Dong-Eon,Kim, Sung-Woong,Yoon, Byung-Hyun,Kang, Hee-Jae,Kang, Nam-Hyun,Cho, Kyung-Mox 한국재료학회 2011 한국재료학회지 Vol.21 No.1
Energy resistance welding (ERW) is a pipe-producing process that has high productivity and low manufacturing cost. However, the high heat input of ERW degrades the mechanical property of the pipe. This study investigates the effect of heat input and alloying elements on microstructure and mechanical properties of ERW pipes. As the heat input increased, the ferrite amount increased. The ferrite amount in the weld centerline was larger than t at in the weld boundary. Medium carbon steels (S45C and K55) having 0.3~0.4wt.% carbon yielded a significant difference of ferrite amount in the weld centerline and weld boundary. High alloyed steels (DP780 and K55) having 1.5~1.6wt.% Mn showed a ferrite rich zone in the weld centerline. These phenomena are probably due to decarburization and demanganisation in the weld centerline. As the ferrite fraction increased, the hardness decreased a little for the S45C steels. In addition, DP780 steels and K55 steels showed that the hardness drops when those steels have a ferrite rich zone. But we demonstrated the good tensile property of the DP780 steels and K55 steels in which Mn is included.