材料期刊网

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(f0)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 diagram (FLD) is an important performance index to describe the maximum limit of principal strains that can be sustained by sheet metals till to the onset of localized necking. It offers a convenient and useful tool to predict the forming limit in the sheet metal forming processes. In the present study, FLD has been determined experimentally for Ti?6Al?4V alloy at 400 °C by conducting a Nakazima test with specimens of different widths. Additionally, for theoretical FLD prediction, various anisotropic yield criteria (Barlat 1989, Barlat 1996, Hill 1993) and different hardening models viz., Hollomon power law (HPL), Johnson?Cook (JC), modified Zerilli–Armstrong (m-ZA), modified Arrhenius (m-Arr) models have been developed. Theoretical FLDs have been determined using Marciniak and Kuczynski (M?K) theory incorporating the developed yield criteria and constitutive models. It has been observed that the effect of yield model is more pronounced than the effect of constitutive model for theoretical FLDs prediction. However, the value of thickness imperfection factor (f0) is solely dependent on hardening model. Hill (1993) yield criterion is best suited for FLD prediction in the right hand side region. Moreover, Barlat (1989) yield criterion is best suited for FLD prediction in left hand side region. Therefore, the proposed hybrid FLD in combination with Barlat (1989) and Hill (1993) yield models with m-Arr hardening model is in the best agreement with experimental FLD.