先進高強度鋼板材料模型與成形工法之研究

Material Models and Forming Processes of Advanced High Strength Steels

蘇柏銓(Po-Chuan Su)

指導教授 ： 陳復國

國立臺灣大學/工學院/機械工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.10512

摘要

當今世界汽車工業在鋼板開發方面有著顯著的趨勢：汽車工業在安全性與經濟耗油性已取得巨大進步。這些進步與汽車工業對於各種先進高強度鋼板的成功研製密不可分。通常對於相同等級車型之汽車，在保證其使用安全性的前提下，降低重量大多會透過採用重量輕而強度高的鋼板製造零件和結構件來實現，而多年來國際車廠與鋼廠投入大量之研究使得採用輕量化、高強度的鋼板更切實可行。
但是隨著鋼板強度的提高，其沖壓成形所面臨之破裂、回彈等成形缺陷相較於傳統低強度鋼更為嚴重。針對高強度鋼板之成形問題，目前國際間產學研各界已紛紛投入高強度鋼之材料模型研究，包括考慮包辛格效應(Bauschinger effect)之加工硬化準則以及考慮雙軸向受力行為之降伏準則，期望藉由瞭解材料的塑性變形特性，提升對於高強度鋼板沖壓成形特性分析與回彈預測之能力。
本論文首先針對目前常用之Hill48、Hill90、Barlat89、Barlat91和Yld2000-2d等降伏準則進行探討，並執行建立降伏準則所需之實驗，包括：單軸拉伸實驗、雙軸拉伸實驗和塑性應變指數實驗。其中雙軸拉伸實驗係使用本實驗室設計之雙軸拉伸夾治具機構進行，根據實驗數據探討適合描述高強度鋼板在塑性應變變形行為之降伏準則，並建立有限元素分析所需之各降伏準則材料模型參數。由文獻可知，包辛格效應對於提升回彈預測準確性有很大的幫助，因此本論文亦建立可以描述包辛格效應之Yoshida-Uemori材料模型，以及該材料模型所需之參數。
材料模型對於有限元素回彈模擬分析之準確性有所影響，而成形工法亦對於回彈有明確的影響。因此本論文探討不同成形工法對於隧型樑造型工件沖壓成形所產生回彈之影響，亦探討隧型樑造型參數對於回彈之影響性。最後，本論文探討最適合該工法之造型參數並建立各工法對於不同回彈種類之經驗公式，以提供日後開發之參考。
本論文同時針對590R強度之汽車結構件沖壓成形進行有限元素法分析以及實際部品開發驗證。在完成上述所建立之材料模型與工法探討後，本論文結合考慮包辛格效應之Yoshida-Uemori材料模型搭配不同降伏準則，應用於業界汽車載具沖壓成形模擬分析，比較模擬與實驗之厚度與回彈結果，其結果顯示Yld2000-2d降伏準則結合Yoshida-Uemori材料模型與實際結果最為相近。

關鍵字

先進高強度鋼板 ； 材料模型 ； 包辛格效應 ； 降伏準則 ； 雙軸拉伸試驗 ； 成形工法 ； 有限元素法分析

並列摘要

In order to cope with the energy crisis problem and the rising importance of collision regulations, reducing weight and increasing strength of an automotive structure are the goals for the major car manufacturers at present and therefore advanced high strength steel has been widely used in automotive structures in this situation.
Although the advanced high strength steel has high strength and low cost characteristics, the formability is much poorer than that of traditional low strength steels. The defects of crack, wrinkle and springback are much easier to present in the forming of advanced high strength steel sheets. To overcome these problems, recent studies began to develop material models to understand the forming characteristics of advanced high strength steel sheets and to improve the accuracy of the finite element simulations.
In order to evaluate the published material models and establish the material constants used in these models, the applicability of yield criteria, such as Hill48, Hill90, Barlat89, Barlat91 and Yld2000-2d for describing the plastic deformation of the advanced high strength steel was investigated first in this thesis. The yield loci, yield stress and r-value directionalities predicted with the use of Hill48, Hill90, Barlat89, Barlat91 and Yld2000-2d, respectively, for the advanced high strength steels were constructed. The finite element simulations for the V-bending and U-hat forming process with the advanced high strength steel sheets were performed to compute the springbacks and side-wall curls. The predicted profiles were compared to experimental data and it was shown that the finite element simulation using the Yld2000-2d yield criterion led to the best agreement between the simulation results and experimental data. Also according to the literature survey conducted in this thesis, it reveals that the Yoshida-Uemori model is suitable to describe the Bauschinger’s effect and its model would improve the springback prediction.
The forming process is also a key factor that affects the presence of springback. Therefore, the stamping of a U-channel part with different forming processes was examined by the finite element simulations and the springback occurred in each process was recorded and compared with. After quantifying of the springback, we could use the numerical software to generate an empirical equation and it would be a very useful reference for the tooling design for stamping of the advanced high strength steel sheets.
With the determined material constants used in the material models, the forming of a B-pillar with advanced high strength steel sheet was investigated in this thesis by the finite element simulations. The comparison of the simulation results and experimental data in terms of deformed sheet thickness and springback indicates that the use of Yld2000-2d yield criterion in conjunction with the Yoshida-Uemori model is very effective in the springback prediction of advanced high strength steel stamping.

並列關鍵字

advanced high strength steel ； material model ； Bauschinger effect ； yield criterion ； biaxial stretching tests ； forming process ； finite element analysis

參考文獻

[5] 劉士維, “先進高強度鋼板沖壓成形之回彈分析”, 國立台灣大學機械工程研究所碩士論文, 2008.

[18] 蔡恒光, “先進高強度鋼板反覆拉壓與雙軸拉伸變形特性之研究”, 國立台灣大學機械工程研究所博士論文, 2012.

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