不同强化模型下的板料成形极限

FORMING LIMIT OF SHEET METALS BASED ON DIFFERENT HARDENING MODELS

介绍HiIl48屈服准则下基于不同强化模型的屈服方程。推导出能够用来确定随动强化模型和混合强化模型中参数的方程。采用单向拉伸曲线上所取得的数据,对所得方程进行拟合,得到参数值,并使用所得参数值得出三种强化模型下的单向拉伸曲线。结果表明采用上述方法能够准确地确定强化模型中的参数。给出随动强化模型和混合强化模型下成形极限的计算方法。基于三种强化模型,针对分散性失稳准则、Hill集中性失稳准则、凹槽失稳准则和平面应变漂移失稳准则,得到简单加载路径下的成形极限图和成形极限应力图。从这些图中可以看出,强化模型对成形极限图和成形极限应力图影响明显。因此应当确定板料在成形过程中的强化规律,选择合适的强化模型进行成形极限预测。

Yield functions based on different hardening models are introduced according to Hill48 yield criterion. A function, which can be used to identify the parameters of kinematic hardening model and mixed hardening model, is derived. The values of parameters are obtained by fitting the function with data of uniaxial tension curve and uniaxial tension curves based on three hardening models are obtained with these parameters. The results show that the above approach can accurately determine the diameters of hardening models. The approach to calculate the forming limit based on kinematic hardening model and mixed hardening model is advanced. Forming limit diagrams and forming limit stress diagrams are obtained under simple loading path based on three hardening models according to diffuse instability theory, Hill localized instability theory, groove instability and plane strain floating instability theory. From the diagrams, it can be found that hardening model can influence forming limit diagrams and forming limit stress dia- grams obviously. Therefore, hardening rule in sheet metal forming process should he identified in order to select proper hardening model to predict the forming limit.