제동 디스크용 주철의 물성 및 열피로 특성평가

구병춘,임충환,Goo, Byeong-Choon,Lim, Choong-Hwan 대한기계학회 2012 대한기계학회논문집 Vol.36 No.8

철도차량의 제동 디스크에 사용될 수 있는 주물재료 4 종에 대해 인장강도, 압축강도, 경도, 비열, 비중, 열전도도 등 여러 특성값을 측정하였다. Ni, Cr, Mo 의 조성비에 따라 인장강도, 압축강도, 경도 등을 조절할 수 있었다. 이들 재료에 대해 열피로 시험을 수행할 수 있는 장치를 사용하여 원통형 시편에 대해 열크랙의 발생과 길이를 측정하여 재료의 내열성을 평가하였다. 그리고 열피로 시험과정을 유한요소법으로 해석하고 Manson-Coffin 식과 주변형률을 이용하여 열피로수명을 평가하여 시험결과와 비교, 검토하였다. 해석에 의한 예측수명은 관찰영역의 균열의 총 길이가 $40{\mu}m{\sim}1mm$ 사이에 있을 때의 수명에 해당함을 알 수 있다. We measured the mechanical and thermal properties of four types of cast irons used for manufacturing the brake discs of railway vehicles. It was found that these properties could be controlled by varying the composition of Ni, Cr, and Mo. Thermal fatigue tests were carried out by using a thermal fatigue tester in which thermal cycles could be controlled. Thermal crack initiation and propagation were measured on cylindrical specimens. Finally, we simulated the thermal fatigue test procedure by finite element analysis and calculated the thermal fatigue lifetimes by Manson-Coffin's equation and the maximum principal strain. The estimated thermal fatigue lifetimes corresponded to the measured lifetimes when the total crack length was $40{\mu}m{\sim}1mm$.

Al6061-T6 판재의 마찰교반용접 3D 유한요소 해석

구병춘,정현승,Goo, Byeong-Choon,Jung, Hyun-Seung 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.4

Friction stir welding (FSW) is a solid state joining method patented in 1991 by The Welding Institute (TWI). It is widely used for joining light metals such as Al and Mg alloys. Foreign railway vehicle manufacturing companies have been applying FSW to car body welding, but domestic companies are in the beginning of feasibility study. Therefore, lots of experimental and analytical study is needed. In this study, three-dimensional finite element modeling of the friction stir welding of two Al6061-T6 plates was carried out. And temperature field and residual stresses were obtained and compared to experimental results in the literature. It is found the analytic thermal field is in a good agreement with the experimental results, but there are some differences between numerical and experimental residual stresses.

계장화 압입시험에 의한 용접부의 물성 측정 및 피로수명 예측

구병춘,이동형,권동일,최열,Goo, Byeong-Choon,Lee, Dong-Hyung,Kwon, Dong-Il,Choi, Yeol 한국철도학회 2004 한국철도학회논문집 Vol.7 No.2

When material properties depend much on positions in a material or it is difficult to make test specimens from a material or component, an instrumented indentation test described in ISO 14577-1, 14577-2 or KS B 0950 can be used to measure material properties and damage. In this study, first of all, the principals of the instrumented indentation test, KS B 0950 are introduced and yield strengths, tensile strengths and work hardening exponents of base materials, heat affected zones and weld materials are measured. In addition, the influence of post-weld heat treatment on the material properties is investigated. Finally the fatigue lift of butt welded specimens are evaluated by the local strain approach. To calculate local strains and stresses, elasto-plastic finite element analysis is conducted using the measured properties.

용접부의 피로강도 시험평가 및 해외규격과의 비교연구

구병춘,김재훈,Goo, Byeong-Choon,Kim, Jai-Hoon 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.1

A lot of fatigue tests on a material, JIS SM490A, with yielding strength of about 350 MPa and tensile strength of about 520 MPa were carried out. Various butt-welded specimens such as reinforcement removed, as-welded and weld toe ground, several types of fillet-welded specimens and full-size box type components were used. After having obtained S-N curves for the above- mentioned specimens, fatigue strengths were compared to those of foreign design codes, AWS, BS 7608 and ENV. It was found the fatigue strengths at low cycles are not in a good agreement with the foreign codes, but the fatigue limits are in a good agreement.

철도차량 구조물의 확률론적 피로수명 평가 연구

구병춘(Byeongchoon Goo),서정원(Jungwon Seo),정홍채(Heungchai Jung) 한국자동차공학회 2002 한국자동차공학회 Symposium Vol.2002 No.11

In case of the fatigue life evaluation of rolling stock structures, mainly deterministic fatigue life evaluation has been carried out. But most of the parameters influencing on the fatigue life have a probabilistic distribution such as normal, log-normal, Weibull, etc. Therefore, to take probabilistic factors into fatigue life evaluation, probabilistic methods are being applied to the fatigue life evaluation of rolling stock. In this paper, probabilistic S-N analysis and methods using limit state functions are introduced. And some results of fatigue life evaluation obtained with these methods for rolling stock structures are shown.

잔류응력이 SM490A의 기계적 거동에 미치는 영향

구병춘(Byeongchoon Goo),양승용(Sungyong Yang) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Residual stresses play an important role in the mechanical behaviour of steels. To examine the effect of residual stresses on tensile behaviour, residual stresses in the specimens were generated by welding. Experimental stress-strain curves of the specimens with/without residual stresses were obtained and compared to simulated curves obtained by the finite element analysis. The two results are in a good agreement. Finally, to study the relaxation of the residual stresses during fatigue crack propagation, we carried out fatigue crack propagation analysis by the finite element analysis.

경도를 이용한 피로수명 평가에 관한 연구

구병춘(Byeongchoon Goo),양승용(Seungyong Yang) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.5_2

To evaluate the fatigue lifetime of structures, it is necessary to identify the value of parameters through tests or literature. it is difficult for field engineers to get the necessary data through tests from the viewpoint of time and cost. In this study, we surveyed literature and proposed a procedure to identify the fatigue parameters for fatigue life evaluation by local strain approach and then we evaluated the fatigue lifetime for several kinds of welded joints. The simulated results are in a good agreement with experimental results.

열화상 이미지와 유한요소법에 의한 제동 디스크/패드의 접촉압력 해석

구병춘(Byeong-Choon Goo),이찬우(Chan-Woo Lee),김민수(Min-Soo Kim) 한국철도학회 2018 한국철도학회 학술발표대회논문집 Vol.2018 No.10

계장화 압입시험에 의한 용접부의 물성 측정 및 피로수명 예측

구병춘(Byeong-Choon Goo),이동형(Dong-Hyung Lee),권동일(Dong-Il Kwon),최열(Yeol Choi) 한국철도학회 2004 철도저널 Vol.7 No.2

When material properties depend much on positions in a material or it is difficult to make test specimens from a material or component, an instrumented indentation test described in ISO 14577-1, 14577-2 or KS B 0950 can be used to measure material properties and damage. In this study, first of all, the principals of the instrumented indentation test, KS B 0950 are introduced and yield strengths, tensile strengths and work hardening exponents of base materials, heat affected zones and weld materials are measured. In addition, the influence of post-weld heat treatment on the material properties is investigated. Finally the fatigue life of butt welded specimens are evaluated by the local strain approach. To calculate local strains and stresses, elasto-plastic finite element analysis is conducted using the measured properties.

파괴역학을 이용한 차륜과 레일의 마모에 관한 연구

구병춘(Goo Byeong-Choon) 한국철도학회 1998 한국철도학회 학술발표대회논문집 Vol.- No.-

A two dimensional elasto-plastic finite element program taking into account contact between crack surfaces is developed in order to analyze subsurface cracking in rolling contact. But the friction between upper and lower surface of the crack is not considered. Under the assumptions of small deformation and small displacement, the incremental theory of plasticity is used to describe plastic deformation. J-integral is computed as the applied Hertzian load slides over the surface with friction. J-integral is correlated with wear rate of the rail. The propagation rate of the right tip of the subsurface crack is fast by 45% than that of the left side.