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경량 차체용 고장력 강판의 Spot 용접과 피로설계에 관한 연구
허정범(Jeongbeom Heo),배동호(Dongho Bae),윤치상(Chisang Yoon),권순용(Soonyong Kwon) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
The recent tendency in the automobile industries is toward light weighting vehicle body to improve the<br/> problems by environmental pollution as well as improving fuel cost. The effective way to reduce the weight<br/> of vehicle body seems to be application of new materials for body structure and such trend is remarkable.<br/> Among the various materials for vehicle body, stainless steel sheet (for example, 301L and 304L), TRIP steel<br/> and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material<br/> and to establish the long life design criteria of body structure, it is important and require condition to assess<br/> spot weldability of them and fatigue strength of spot welded lap joints which were fabricated under optimized<br/> spot welding condition. And, recently, a new issue in the design of the spot welded structure is to predict<br/> economically fatigue design criterion without additional fatigue tests. In general, for fatigue design of the<br/> spot-welded thin sheet structure, additional fatigue tests according to the welding condition, material, joint<br/> type, and fatigue loading condition are generally required. This indicates that much cost and time for it should<br/> be consumed. Therefore, in this paper, the maximum stresses at nugget edge of spot weld were calculated<br/> through nonlinear finite element analysis first. And next, obtained the f N P . . relation through the actual<br/> fatigue tests on spot welded lap joints of similar and dissimilar high strength steel sheets. And then, the<br/> relation was rearranged in the Δ f N P . . σ- N f relation. From this Δ σ - N f relation, developed the<br/> fatigue design technology for spot welded lap joints of them welded using the optimized welding conditions.
양우열(WooYul Yang),이승열(Seung Yeol Lee),금영탁(YoungTag keum),황진영(JinYoung Hwang),윤치상(ChiSang Yoon),신철수(ChirlSoo Shin),조원석(WonSuk Cho) 한국자동차공학회 2002 한국자동차공학회 Symposium Vol.2002 No.11
In order to develope springback reduction technology for high-strength steel sheets, 3 studies have been conducted: dome stretching tests, stepped s-rail forming and springback measurement, and optimally shaped initial blank design. First, to find out the formability of TRIP60, dome stretching test was performed. Next, the stepped s-rail die, which was designed to form a channel type panel with large twist and wall curl, was manufactured and used to know the effect of controlling forming variables, such as blank holding force and flange amount on the springback. Furthermore, new measurement technology of the springback was introduced to define wall curl and twist in geometrically complex panels. Finally, the optimally shaped initial blank was employed to verify one of the best ways to reduce the springback in chanel type, high strength sheet panels.
차체경량화를 위한 고강도 강판의 점 용접성과 피로강도 평가
배동호(Dongho Bae),손일선(Ilseon Sohn),정원석(Wonseok Jung),허정범(Jeongbeom Heo),권순용(Soonyong Kwon),윤치상(Chisang Yoon) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The recent tendency in the automobile industries is toward light weighting vehicle body to improve the problems by environmental pollution as well as improving fuel cost. The effective way to reduce the weight of vehicle body seems to be application of new materials for body structure, and such trend is remarkable. Among the various materials for vehicle body, stainless steel sheets and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material and to establish the long life fatigue design criteria of body structure, it is necessary to assess spot weldability and fatigue strength of spot welded lap joints fabricated under optimized spot welding condition. In this paper, spot weldability of the stainless steel sheets, STS301L and STS304L, and the cold rolled steel sheets, SPCC and SPCD. Fatigue strength of lap joints spot -welded between similar and dissimilar materials were also assessed.
임지호(Jiho Lim),김석봉(Seokbong Kim),김진성(Jinsung Kim),허훈(Hoon Huh),권순용(Sunyong Kwon),윤치상(Chisang Yoon),박성호(Sungho Park) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
While the formability is important and indispensable for success in very complicated sheet metal forming, it seems that few studies has been carried out about the formability of sheet metal at the high strain rate. The present experimental results report that the elongation is dependent on the crosshead speed in tensile tests. In this paper, the tensile elongation has been obtained from various steel sheets for an auto-body at the intermediate strain rate. The strain rate in the experiment is ranged from 0.003/sec to 200/sec. The experimental result demonstrates that the tensile elongation does not decrease as the strain rate increases. This tendency has varieties depending on the microstructure and forming history of sheet metal. Some high strength steels have the tendency that the tensile elongation increases as the strain rate increases, while others not. This phenomenon is very important not only in sheet metal forming but also in the crash worthiness evaluation to predict the fracture and tearing of sheet metal members.