雙軸拉伸試驗夾治具機構與試片形狀之優化設計

車體輕量化是國際間各大汽車廠努力之目標。為兼顧生產成本以及達成車輛輕量化之目標，汽車結構件使用先進高強度鋼板已成為國際車廠的共同趨勢。但因鋼板強度之提升，沖壓成形更加困難，且側壁外開、側壁捲曲等缺陷亦更加嚴重。對於高強度鋼板之沖壓成形問題，國際間產學研各界已紛紛投入高強度鋼板之材料模型研究，其中包含考慮材料包辛格效應之加工硬化準則及考慮雙軸向受力行為之降伏準則，藉由瞭解材料之塑性變形特性，提升高強度鋼板沖壓成形特性分析與回彈預測之能力。加工硬化準則方面，本實驗室已完成建立先進高強度鋼板之Yoshida-Uemori材料模型參數。因此本研究的重點為建立適用於先進高強度鋼板雙軸受力下之降伏準則。首先，改良雙軸夾治具機構之設計，使其可用於建立目前汽車結構件冷沖壓強度最高之1180級鋼的降伏準則。此雙軸夾治具的另一個特色是可用於單軸單動式材料試驗機，適合產業界的需求。而在雙軸試片方面，由於目前並無雙軸拉伸試片形狀與尺寸之規範。因此，本研究針對文獻中使用之雙軸試片配合本研究開發之雙軸夾治具機構之作動方式進行優化，並設計出最符合本研究之十字形溝槽試片。完成雙軸夾治具機構之改良與雙軸試片設計後，根據實驗數據建立有限元素分析所需之各降伏準則材料模型參數。最後，結合考慮包辛格效應之Yoshida-Uemori材料模型與文獻中常見之降伏準則，進行基礎載具沖壓成形模擬分析與實驗，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

先進高強度鋼板；材料模型；降伏準則；雙軸拉伸試驗；雙軸拉伸試片；有限元素法分析

並列摘要

Because design for lightweight automobiles becomes a major goal for vehicle manufacturers, the use of advanced high strength steels in automobile structural parts manufacture becomes a trend. In order to improving CAE simulation accuracy of stamping processes, recent researches focus on the development of advanced high strength steel material models, taking Bauschinger effect and yield criteria under biaxial stress into consideration. With better understanding of material behaviors during plastic deformation, accurate springback prediction can be achieved. The Yoshida-Uemori model, which considers the Bauschinger effect, for advanced high strength steels was established in our lab. This research aims at exploration of the biaxial tensile test for advanced high strength steels. Thus, a complete material model for advanced high strength steels can be established. In this study, the apparatus for biaxial tensile test is improved. With the design of low friction in this apparatus, it is able to perform the biaxial tensile test of 1180Y steels. As for the specimen for the biaxial tensile test, standards for specimen shape and dimension are not available. Therefore, the specimen geometry is also designed in this research. After the improved biaxial tensile test apparatus is established, the biaxial tensile tests for advanced high strength steels, including grades of 590Y, 780Y, 980Y and 1180Y, are carried out. The parameters for different yield criteria are obtained based on experimental results. Combining the Yoshida-Uemori model and various yield criteria, CAE simulations for V-bending and U-hat stamping are carried out. The comparison of CAE simulations and experimental results shows that the combination of Yld2000-2d yield criterion with Yoshida-Uemori model is most appropriate in springback prediction of stamping advanced high strength steels.