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Please use this identifier to cite or link to this item:
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/35420
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| Title: | 金屬板材方杯拉伸裂紋成長之預測 |
| Other Titles: | Prediction of crack propagation in the square-cup stretching process of sheet metal |
| Authors: | 劉得仁;Liu, De-ren |
| Contributors: | 淡江大學機械與機電工程學系碩士班
李經倫;Li, Ching-lun |
| Keywords: | 方杯拉伸;顯性動態有限元素;裂紋成長;Square-Cup Stretching;Dynamic Explicit Finite Element;Crack Propagation |
| Date: | 2006 |
| Issue Date: | 2010-01-11 06:31:01 (UTC+8) |
| Abstract: | 本文採用顯性動態有限元素法，結合材料彈塑性理論，發展出一套三維增量型之有限元素分析程式，進行金屬板材方杯拉伸成形製程及破裂之分析，並探討方杯拉伸成形歷程及裂紋成長歷程、工件厚度變化、成形極限圖(Forming Limit Diagram, FLD)，及沖頭負荷與衝程關係，並設計一組方形沖模來進行方杯拉伸成形實驗，以驗證程式的可信度。
經由數值模擬與實驗結果比較得知，在方杯拉伸過程中，當沖頭衝程達到13.25mm時，工件沿輥軋方向夾45度角之角隅處已發生破裂，由於此處受到最大的雙軸向拉伸應力，因此最大等效應力、等效應變及厚度最小值，均集中於此區域，並最先達到臨界破裂之應變能密度值140MPa，裂紋將從此處開始發生，而拉伸成形之最大沖頭負荷則隨著沖模平行邊入模圓弧角半徑，與沖頭底邊圓弧角半徑之遞增而遞減。方杯拉伸成形中，當沖頭衝程達13.05mm時，由其主應變值及次應變值所繪製出之成形極限圖可知，工件已達到頸縮不穩定之範圍，而方杯拉伸在沖頭衝程達13.25mm時，由其成形極限圖中之應變分佈可知，工件已達到破裂之範圍。數值模擬之結果皆可合理的模擬實驗結果，故本顯性動態有限元素分析程式，可合理預測方杯拉伸成形極限。
The objective of this study was to analyze the square cup stretching process by using the dynamic explicit finite element analytical program, which was based on the Updated Lagrangian Formulation and elasto-plastic theory. Simulation results included the deformation and crack propagation history, the variation of the work piece thickness, the Forming Limit Diagram (FLD), and the relationship between punch load and punch stroke. A set of tools was designed for the square-cup stretching experiment to verify the reliability of the program.
According to the experiment and simulation results, when the punch stroke attained 13.25mm, the contact regions between workpiece and punch corners has fractured, because it absorbed the maximum biaxial stretching stress, so the minimum thickness, the maximum effective stress and maximum effective strain were all concentrated on here, and it’s strain energy density also first reached the limit fracture value 140MPa, then the crack propagation started. Moreover, the maximum punch load decreased as the die arc radius or punch profile radius became larger. According to the forming limit diagram, we found that when the punch stroke attained 13.05mm, the workpiece may start necking, and the workpiece started to fracture when punch stroke attained 13.25mm. The simulation results good agreement with experiment results, so the dynamic explicit finite element program can simulate the square-cup stretching process reasonably. |
| Appears in Collections: | [機械與機電工程學系暨研究所] 學位論文
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