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成形极限图是一种用来描述使板材不发生局部颈缩所需最大主应变的重要图形。它是一种预测板材变形过程中变形极限的方便、有效的工具。本研究中,在400°C和不同样品宽度的条件,通过Nakazima实验得到了Ti-6Al-4V合金的成形极限图。此外,为了使用成形极限图对材料参数进行理论预测,提出了不同的各向异性屈服准则(Barlat 1989,Barlat 1996,Hill 1993)和不同的硬化模型(Hollomon幂定律、Johnson-Cook(JC)模型、改进的Zerilli-Armstrong(m-ZA)和Arrhenius(m-Arr)模型)。结合所提出的屈服准则和本构模型,通过Marciniak和Kuczynski(M-K)理论确定了Ti-6Al-4V合金的成形极限图。结果表明:屈服模型对材料成形极限图的影响大于本构模型的影响。然而,材料的厚度缺陷系数(f_0)与其硬化模型密切相关。Hill(1993)屈服准则最适合于成形极限图右边区域的预测,而Barlat(1989)屈服准最适合于成形极限图左边区域的预测。由于所得到的混合理论成形极限图兼具Barlat(1989)和Hill(1993)屈服模型和m-Arr硬化模型的优点,因此,它与实验得到的成形极限图吻合很好。
Forming limit map is an important figure used to describe the maximum principal strain required to make a plate without local necking. It is a convenient and effective tool for predicting the deformation limit in sheet metal deformation. In this study, the forming limits of Ti-6Al-4V alloy were obtained by Nakazima test at 400 ° C and different sample widths. In addition, different anisotropic yield criteria (Barlat 1989, Barlat 1996, Hill 1993) and different hardening models (Hollomon’s Law of Power, Johnson-Cook (JC) model , Improved Zerilli-Armstrong (m-ZA) and Arrhenius (m-Arr) models). Combined with the proposed yield criterion and constitutive model, the forming limit of Ti-6Al-4V alloy was determined by Marciniak and Kuczynski (M-K) theory. The results show that the influence of yield model on the material forming limit graph is larger than that of the constitutive model. However, the material’s thickness defect coefficient (f_0) is closely related to its hardening model. The Hill (1993) yield criterion is best suited for the prediction of the right-hand side of the limit-of-forming plot, whereas Barlat (1989) yielding is best suited for the prediction of the left-hand side of the limit-of-forming plot. Since the resulting mixed theoretical formations have both the advantages of the Barlat (1989) and Hill (1993) yield models and the m-Arr hardening model, it fits well with the experimental forming limit plots.