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크리프-피로 상호작용하의 P29강 용접부의 모재와 열영향부의 균열성장거동에 미치는 유지시간의 영향
임병수(Byeongsoo Lim),김범준(Bumjoon Kim),진명진(Myungjin Jin) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
In this study, the crack growth behavior in P92 steel (9%Cr~2%W) weldment was investigated at 600℃ under the load of trapezoidal wave shape with various hold times. The creep-fatigue crack growth behavior of the HAZ(heat affected zone) and base metal is compared. The relationship between the crack growth behavior and dwell time was studied and it was characterized using the △K and (C₁)_avg prarmeters. Also, the fracture mode was investigated. The relationship between crack growth rate and hold period and crack propagation path were investigated.
임병수(Byeongsoo Lim),류승진(Seungjin Ryu),김대욱(D. Kim) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.5_2
The use of aluminum alloys is an attractive possible option in order to reduce the weight of automobile body structures to achieve the subsequent improvement of fuel economy and driving performance. Aluminum resistance spot welding(Al RSW), similar to current steel automobile body construction, may be considered one of the manufacturing methods for an aluminum body structure. Due to the unreliable durability of weld-bonded joints, applications of Al RSW are limited. A patented post-weld cold working process was used to improve the fatigue strength of Al RSW. The post-weld cold working process includes that special shaped indenters are pressed or driven into the structure in order to induce the compressive residual stresses. The effect of the post-weld cold working process parameters on the fatigue strength of the Al RSW was investigated. Comparisons of the fatigue properties and qualitative results between the as-welded RSW specimens and the post-weld cold worked RSW specimens are discussed.
P92강 용접부의 크리프-피로균열성장거동과 미세 조직적 손상에 미치는 유지시간의 영향
임병수(Byeongsoo Lim),김범준(Bumjoon Kim) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
In this study, the crack growth behavior in P92 steel (9%Cr-2%W) weldment was investigated at 600℃ under the load of trapezoidal wave shape with various hold times. The relationship between the crack growth behavior and hold time was studied and it was characterized using △K and (Ct)avg parameter. Also, the number of micro-voids/cavities at the crack tip and fracture mode was investigated. The relationship between crack growth rate and hold period and crack propagation path were investigated.
초음파를 이용한 구조물 내부의 균열 및 미소 결함 검출
임병수(Byeongsoo Lim),배시연(Siyeon Bae),정찬서(Chanseo Jeong) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The initiation and growth of internal defects usually cause the failure of long term operated structural components at high temperature. Therefore, by investigating the internal defects of material, the integrity of the system can be maintained and the unexpected failure can be prevented. The main purpose of this study is to investigate the possibility of the application of ultrasound to the measurement and estimation of the creep damage. In this study, the phased array ultrasound and backward ultrasound were employed to detect the internal defects caused by creep. The former is suitable for the detection of defects existing deep in structure while the latter is for the defects on the surface or in shallow region. Using the newly developed P92 steel. both creep and NDE ultrasound tests were performed. The results of defect inspection were checked by microstructure examination. Reliable information on the size and position of crack were obtained and successful estimation of the amount of micro-voids and their distribution proved to be obtainable by the ultrasound inspection technique. The width of the creep degraded zone was confirmed by the width of ultrasonic signal, and the severity of degradation was confirmed by ultrasonic amplitude.
임병수(Byeongsoo Lim),진명진(Myungjin Jin),김민혁(Minhyuk Kim) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.5_2
The purpose of this study is to investigate the fatigue crack growth behavior of P23 alloy at high temperature. Fatigue tests were performed using compact tension specimens at 500~600℃, with the load frequency of 20~0.01㎐. The fatigue crack growth behavior was characterized using ΔK parameter. The crack growth rate was found to be greater at lower frequency and higher temperature. From the results of microstructural examination, it was found that in all tests, the crack growth path was transgranular. The crack growth behavior was found to be cyclic dependant with branch cracks at 20㎐ and 1㎐. At 0.01㎐, it was time dependant with a single crack induced by oxidation.
P92강 용접부의 피로균열 성장거동에 미치는 미세조직의 영향
김범준(Bumjoon Kim),임병수(Byeongsoo Lim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8
Fatigue strength and life of weldment at high temperature is very important for high temperature materials used in power plants. In this study, fatigue crack growth tests were performed to examine the effect of microstructure on the crack growth resistance in P92 steel weldment. Microhardness of the weldment was also investigated for better analysis. Residual stresses were removed by heat treatment to focus the study on the microstructural effect. CT specimens were made from the welded plate with notch at different distances from the fusion line. The fatigue crack growth rate was found highest along the fusion line and fusion line+2㎜ line into the heat affected zone.
[재료] STS 316L의 고온 피로균열에 미치는 인장유지시간의 효과
김문진(Moonjin Kim),임병수(Byeongsoo Lim) 한국자동차공학회 1999 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1999 No.11_2
The heat resistant material, in service, may experience static loading cyclic loading, or a combination of two. An experimental study of crack growth behavior of STS 316L austenitic stainless steel under fatigue, and creep-fatigue loading conditions were carried out on compact tension specimens at various tensile hold times. In the crack growth experiments under hold time loading conditions, tensile hold times were ranged from 5 seconds to 100 seconds and its behavior was characterized using the ??K parameter.<br/> The crack growth rates generally increase with increasing hold times. However in this material, the trend of crack growth rates decreases with increasing hold times for short hold time range relatively. It is attributed to a decline in the cyclic crack growth rate as a result of blunting at the crack tip by creep deformation<br/>
[재료] 결정립 크기에 따른 STS 316L강의 크리프 거동에 관한 연구
노연호(Younho Rho),임병수(Byeongsoo Lim) 한국자동차공학회 1999 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1999 No.11_2
The effect of grain size on the creep behavior of low carbon type 316L austenitic stainless steel was investigated. Specimens with grain size of 30. 60 and 125㎛ were prepared through various heat treatments and they were employed in the investigation of the relationship between the grain size and the change of fractional portion of three creep stages.<br/> SEM studies on deformed specimens showed the different roles of grain boundaries in different specimens and the effect of cavities on rupture life of each specimen. The fracture mode of 316L changed from transgranular to intergranular with increasing grain size.<br/>
냉간가공에 의한 자동차 차체용 강 점용접의 피로수명 향상
김민혁(Minhyuk Kim),임병수(Byeongsoo Lim),류승진(Seungjin Ryu),김대욱(D. Kim) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Resistance spot welding (RSW), or spot-welding, is still the most frequently used sheet metal fabrication process for automotive body applications. The optimization of the number, location, and quality of spot welds is a major economic consideration. In order to improve fatigue strength of low carbon steel RSWs, a post-weld cold working processhas been recently introduced. The post-weld cold working process on the spot weld joints generates uniform and consistent large zones of compressive residual stresses using a specially designed indentation device. The compressive residual stress distributions on the RSWs can be modified through the cold working process parameters including cold working pressure and indenter size. The effect of the indenting pressure during the cold working process on the fatigue properties of the low carbon steel spot weldments is investigated. Comparisons of the fatigue strength and fractography between the as-resistance spot-welded specimens and the post-weld cold worked resistance spot-weld specimens are made in this investigation.