考慮兩種破壞準則下碳鋼棒材冷抽成形破壞條件的數值模擬分析

許維驛(WEI-YI HSU)

指導教授 ： 敖仲寧

國立中正大學/工學院/機械工程學系/碩士(2016年)

摘要

冷抽加工技術適用於碳鋼及各類金屬成形，近年來冷抽加工技術更應用在管材、棒材及非對稱型材冷抽。冷抽成形製程處於常溫或再結晶溫度以下，於金屬材料前端施以拉力，使欲加工之型材通過模具，並得到與模具定徑區相同之截面形狀。冷抽加工最關鍵之技術在於模具設計，模具設計不佳會使工件通過模眼時，因裁減量過大導致成形後品質不佳與發生表面或內部破壞的情形，因此如何適當的設計模眼形狀極為重要。
本研究使用有限元素法探討人字紋缺陷(Chevron crack)及表面缺陷(Surface crack)發生之原因，利用數值模擬軟體SIMUFACT與MSC.Marc分析中碳鋼圓棒材冷抽加工過程。配合Lemaitre破壞準則模擬出破壞可能發生的區域以及Oyane破壞準則真實模擬出工件上可能的缺陷形式，並討論兩種破壞準則在不同冷抽參數下對人字紋缺陷及表面缺陷的敏感程度。藉由改變冷抽製程參數比較兩種破壞準則的結果並討論冷抽製程參數對破壞形式的影響，並討論週期性人字紋缺陷之發生條件。利用破壞參數的臨界值，選擇合適的製程參數以確保在冷抽過程中工件皆不致在表面或中心產生缺陷。
於模擬方面使用SIMUFACT數值模擬軟體作為建立數值模型與分析之工具，並使用MSC.Marc討論不同元素尺寸對人字紋缺陷及表面缺陷呈現的影響。

關鍵字

冷抽 ； 中碳鋼圓棒 ； 有限元素法 ； 人字紋缺陷 ； 表面缺陷 ； Lemaitre破壞準則 ； Oyane破壞準則

並列摘要

Cold draw process technology is widely applied in metal forming, especially in pipe, bar and wire manufacturing. During cold draw, metallic materials are drawn through a die at room temperature or temperature below recrystallization temperature to obtain a uniform cross-section profile. Die design, including reduction of area, die angle and friction coefficient, and number of cold pass are critical factors which influence the formability and quality of the end products and the possible defects of fracture occurred during drawing.
In this research, possible conditions for the formation of the chevron crack (or central bursting) and/or surface crack of circular bars during cold draw process are simulated and predicted by using finite element software, SIMUFACT and MSC.MARC. The effect of die angle, friction coefficient and reduction of area on the deformation and the formability is to be evaluated by considering two developed damage models, Oyane damage criterion and Lemaitre damage criterion. The parameter windows and the instance of crack initiation of these two criteria will be compared. In addition, the stress development and distribution, and the damage value distribution are investigated during cold draw simulation process. The process conditions to find central bursting and/or surface cracks are predicted under various process conditions and material properties.

並列關鍵字

Cold draw ； circular bars ； central bursting, ； surface crack ； finite element ； Oyane damage criterion ； Lemaitre damage criterion

參考文獻

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[5] M. Oyane, Criteria for ductile fracture and their applications, Journal of Mechanical Working Technology, Vol.4 (1980), pp.65-81

[6] J. Lemaitre and J.P. Sermage, One damage law for different mechanisms, Computational Mechanics, Vol.20 (1997), pp.84-88

[9] Moriya Oyane, Criteria of Ductile Fracture Strain, Japan Society of Mechanical Engineers, Vol.15 (1972), pp. 1507–1513

[10] H.C. Kim, Y. Choi, and B.M. Kim, Three-dimensional rigid-plastic element analysis of non-steady-state shaped drawing process, International Journal of Machine Tools & Manufacture, Vol.39 (1999), pp.1135-1155.