Cracks caused by cold bending during shipyard construction were found to be longer in mild steel than in high tensile steel. Because mild steel has better elongation, the cause of such cracking was difficult to ascertain. Bending tests of large number of steel pieces to confirm the effects of multiple parameters, nonlinear finite-element analysis to check strain distribution, and fractography to determine the nature of the fracture indicated that ductile fracture initiated where the strain value was highest, as is generally expected. In the bending tests, the fractures were reproducibly longer in alloys with better ductility. One of the reasons for this phenomenon was that the surface was more hardened by plasma-arc cutting in mild steel because of its high carbon content according to hardness tests on the cutting surfaces. We therefore proposed a new equation to estimate crack length, taking into account three factors: strain, elongation and surface hardness. We showed that the relationship between crack length and the values by the equation explains the results of the bending tests. Additionally, we suggested the possibility that inclusions within an alloy affect the crack length. Cold forming is a general procedure used in shipyards. If inspections fail to find a crack, it may propagate to fatal damage after delivery. This study is therefore useful in preventing the initiation of cracks.
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ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering
June 17–22, 2018
Madrid, Spain
Conference Sponsors:
- Ocean, Offshore and Arctic Engineering Division
ISBN:
978-0-7918-5123-4
PROCEEDINGS PAPER
Dominant Factors Influencing Ductile Fracture on Cutting Surface During Cold Forming
Kazunari Takahashi,
Kazunari Takahashi
Namura Shipbuilding Co., Ltd., Imari, Japan
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Shuichi Yamatoki,
Shuichi Yamatoki
Namura Shipbuilding Co., Ltd., Imari, Japan
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Tetsuya Namegawa,
Tetsuya Namegawa
Nippon Steel & Sumitomo Metal, Futtsu, Japan
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Masahiko Kinoshita,
Masahiko Kinoshita
Nippon Steel & Sumitomo Metal, Oita, Japan
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Masaaki Fujioka
Masaaki Fujioka
Nippon Steel & Sumitomo Metal, Futtsu, Japan
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Kazunari Takahashi
Namura Shipbuilding Co., Ltd., Imari, Japan
Shuichi Yamatoki
Namura Shipbuilding Co., Ltd., Imari, Japan
Tetsuya Namegawa
Nippon Steel & Sumitomo Metal, Futtsu, Japan
Masahiko Kinoshita
Nippon Steel & Sumitomo Metal, Oita, Japan
Masaaki Fujioka
Nippon Steel & Sumitomo Metal, Futtsu, Japan
Paper No:
OMAE2018-77177, V004T03A026; 9 pages
Published Online:
September 25, 2018
Citation
Takahashi, K, Yamatoki, S, Namegawa, T, Kinoshita, M, & Fujioka, M. "Dominant Factors Influencing Ductile Fracture on Cutting Surface During Cold Forming." Proceedings of the ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. Volume 4: Materials Technology. Madrid, Spain. June 17–22, 2018. V004T03A026. ASME. https://doi.org/10.1115/OMAE2018-77177
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