A new ductile fracture criterion for the formability prediction of steel sheets and its application to finite element analysis강판의 성형성 예측을 위한 새로운 연성 파괴 조건 및 유한 요소 해석에의 응용

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Sheet metal forming, one of the most important metal working operations, concerns with the shaping of thin metal sheets (normally less than 6 mm or ¼ in.) by applying force to punches and drawing sheets into dies. There processes are accomplished basically by stretching, bending, deep drawing, embossing, bulging, flanging, rolling, and spinning. There are three important issues in sheet metal forming processes: failure, wrinkling and excessive springback. Failure is the focus of this study. Two failure mechanisms are dominant for metals forming: necking and ductile fracture. Necking failure occurs in tension of conventional carbon steels while ductile fracture is observed for advanced high strength steel sheets not only in tension but also in compression and pure shear such as upsetting tests. Necking is widely accepted as the main failure model from the uniaxial tension to the balanced biaxial tension for sheet metals. Failure due to necking is normally expressed by forming limit diagrams (FLDs). In the last decades, many experiments are carried out to construct FLDs of sheet metal alloys such as steel, aluminum and magnesium. Many theoretical models are proposed to predict FLDs such as the Hill’s localized necking model, the Swift’s diffuse necking model, the popular Marciniak and Kuczynski model (M-K model), the vertex theory and the modified maximum force criterion (MMFC). The analytical models above are mainly applied to predict formability of sheet metals based on necking or thickness reduction. Consequently, failure cannot be estimated by these models in low or negative stress triaxiality where there is no or negligible thickness reduction. Metals and alloys usually fail as ductile fracture induced by nucleation, growth and coalescence of microscopic voids. Therefore, ductile fracture occurs in a wide stress state from compressive upsetting to the balanced biaxial tension. A ductile fracture criterion is proposed to model fracture behavior of sheet meta...
Advisors
Huh, Hoonresearcher허훈
Description
한국과학기술원 : 기계공학전공,
Publisher
한국과학기술원
Issue Date
2012
Identifier
511296/325007  / 020075242
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 기계공학전공, 2012.8, [ xx, 198 p. ]

Keywords

Fracture locus; Fracture forming limit diagrams; Ductile fracture; Stress triaxiality; Lode parameter; Ductile fracture; Fracture forming limit diagrams; Fracture locus; Stress triaxiality; Lode parameter; Metal forming; Metal forming

URI
http://hdl.handle.net/10203/181651
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=511296&flag=dissertation
Appears in Collection
ME-Theses_Ph.D.(박사논문)
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