板材成形极限的预测研究

PREDICTION FOR THE FORMING LIMIT OF SHEET METALS

将含有变形损伤效应的本构方程引入到Ｍ－Ｋ理论模型，研究了板材变形失稳和成形极限问题。分析了材料参数及屈服函数对板材成形极限的影响，成形极限曲线的右半部分曲线斜率随应变硬化指数（ｎ值）、应变速率敏感指数（ｍ值）、屈服函数形状系数（Ｍ值）的增大而减小，随材料初始几何缺陷参数（ｆ值）的增大而增大。把改进的Ｍ－Ｋ模型应用于有限元模拟程序，分析了材料参数对板材胀形的极限成形高度的影响，模拟结果与实验结果吻合。

お constitutive relation including the effect of deformation damage has been introduced into the modified MK model to analyse the plastic instability and the forming limit of sheet metals. The effects of material parameters and yield function on the forming limit of sheet metals have been exploded. The slope of the righthand side of the forming limit diagram (FLD) is decreased by increased value of the strainhardening (nvalue), strainrate sensitivity (mvalue), the parameter describing the shape of the yield function (Mvalue), whereas the slope increased with higher the inhomogeneity factor (fvalue). The modified MK model is used into the finite element program to simulate the process of hemispherical punch stretching. The influence of material parameters on the limit cup height at failure (H) has been studied. Theoretically calculated results are in agreement with the experimental results.