先進高強度鋼板材料特性對回彈影響之研究

Effects of Material Characteristics of Advanced High Strength Steel Sheets on Springback

彭彥安(Yan-An Peng)

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(2014年)

https://doi.org/10.6342/NTU.2014.10156

摘要

由於環保意識高漲與消費者對於汽車燃油效率提升之要求，國際間各大車廠均朝向汽車輕量化與強度化發展。因此為了兼顧輕量化與強度化之目標，高強度且低成本特性的高強度鋼板逐漸被廣泛地應用於汽車工業上。
高強度鋼板之成形特性與一般低強度鋼如270級軟鋼有著明顯之差異，其於沖壓成形過程中更容易產生破裂與回彈等缺陷，為了解決高強度鋼板成形之問題，目前各大車廠與板金模具廠均採用有限元素分析輔助模具設計，以達成降低生產成本並有效解決成形缺陷之目標。
針對沖壓成形之有限元素分析，於過去研究文獻中，雖已針對模擬參數進行最佳化之收斂性測試，但對於提升回彈預測之準確度仍有改善空間。因此，本研究將探討考慮包辛格效應(Bauschinger effect)之加工硬化準則、考慮雙軸向受力行為之降伏準則以及高強度鋼與沖壓模具間之摩擦係數，透過探討材料之塑性變形行為，提升對高強度鋼板沖壓成形特性分析與回彈預測之能力。
本研究首先針對目前常用之Hill48、Hill90、Barlat89與Barlat91等降伏準則進行探討，除此之外，也將針對近年來廣受採用考慮多相微觀金屬結構與雙軸受力變形行為之Yld2000-2d降伏準則進行探討，並利用本實驗室設計之實驗夾治具進行雙軸拉伸實驗與夾治具機構摩擦力實驗，根據實驗數據探討適合描述高強度鋼板在雙軸受力下之塑性變形行為的降伏準則，並建立有限元素分析所需之各降伏準則材料模型參數。本研究同時針對Yoshida-Uemori材料模型進行探討，並且由不同分析模擬中發現該材料模型除了考慮包辛格效應對於回彈
預測影響之外，其材料模型中於沖壓成形之卸載(unloading)過程中對於板材楊氏係數之修正，亦會對回彈預測之準確度有所影響，因此本研究將探討於Yoshida-Uemori材料模型中適用於高強度鋼之卸載回歸路徑，以此提升沖壓成形過程中對於回彈預測之準確性。
除了材料模型對於有限元素回彈模擬分析有所影響之外，於沖壓成形過程中板材與模具間之摩擦係數亦對模擬結果有所影響。因此本研究將針對高強度鋼與不同材質之模具進行摩擦係數之實際量測，並透過摩擦試驗過程添加不同之潤滑劑，以此探討其對於成形過程中摩擦係數之穩定性影響。
在完成上述所建立之材料模型與各鋼種之摩擦係數後，本研究即結合考慮包辛格效應之Yoshida-Uemori材料模型搭配不同降伏準則與精確之摩擦係數進行基礎載具與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，可有效提升先進高強度鋼板於沖壓成形模擬之回彈預測準確性。

關鍵字

高強度鋼板 ； 材料模型 ； 包辛格效應 ； Yld2000-2d降伏準則摩擦試驗 ； 雙軸拉伸試驗 ； 有限元素法分

並列摘要

As elevating environmental consciousness and consumer’s demands in enhancing vehicle fuel efficiency, various automobile companies dedicate in developing automobiles with light weight and strength characteristics. Therefore, in order to achieve the goals of light-weight and strength simultaneously, advanced high strength steels (AHSS), with high strength and low cost properties, are widely applied to automobile industry gradually.
The forming characteristics of AHSS substantially differ from than that of low strength steels, for example, 270 mild steels. For instance, defects such as springback are easily occurred during AHSS stamping process. To resolve this issue in AHSS forming, automobile industry and metal mold factories modify module design with finite element analysis, which reduces the cost of production as well as resolves the forming characteristics effectively.
For finite element analysis in stamping , there are numerous studies which investigate and examine the optimum simulation parameters in simulation parameter process , but the accuracy of springback prediction can still be improved. Therefore, this study investigates Bauschinger effect on work hardening criteria, the biaxial stress yield criteria , and the coefficient of friction between the behavior of AHSS and stamping modules.Through exploring plastic deformation, the accuracy of prediction in AHSS stamping forming characteristics analysis and springback can be optimized.
In this study, the yield criteria of Hill48, Hill90, Barlat89, and Barlat91, which are commonly used, will be discussed. In addition, the yield criteria of Yld2000-2d, widely adopted in these years, will also be further discussed in the perspective of micro-term, multi-phase microstructures and biaxial stretching behavior. With using the designed fixtures by our group , the biaxial tensile tests and fixture friction experiments are conducted. Through analyzing the experiment data, we investigate the yield criteria of AHSS with deformation behavior under biaxial stress, and establish the required parameters in diverse materials model for finite element analysis. In this study, the Yoshida-Uemori material model is also discussed. With different simulation models, we find that Bauschinger effect affects the springback prediction. Furthermore, this material model discusses correction of Young’s modulus on stamping unloading process, this also impacts on the precision of springback prediction. Therefore, this study will investigate the unloading regression path of AHSS through Yoshida-Uemori model, hence enhance the accuracy of springback prediction under stamping process.
The materials simulation models may influence finite element analysis for springback. Moreover, the coefficient of friction resulted from the plate and mold during stamping process either has impact on simulation result. Therefore, in this study, we will measure the actual value of coefficient of friction for AHSS and other different materials molds, and add different lubricants through the test of friction. With these, we can further investigate the stability of the forming process for coefficient of
friction.
After completing the material models mentioned above, we will employ Yoshida-Uemori materials model with Bauschinger effect matching with diverse yield criteria and precise coefficients of friction, in order to conduct the stamping simulation analysis of the basic vehicles and the commercial automobile vehicles. By comparing with the thickness and springback of the simulation and experimental results, it shows that Yld2000-2d yield criteria with Yoshida-Uemori models can effectively enhance accuracy of the AHSS in stamping simulation of springback prediction.

並列關鍵字

high strength steel sheet ； material model ； Bauschinger effect ； Yld2000-2d yield criteria ； finite element analysis

參考文獻

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