基于连续介质损伤力学预测7075铝合金热冲压成形极限图

Prediction of FLD for AA7075 under hot stamping based on continuum damage mechanics

针对应用试验方法获得的7075-T6铝合金板材热冲压成形极限图(FLD)的局限性,开展了基于连续介质损伤力学预测7075铝合金热成形FLD的方法研究。提出应用一组单轴黏塑性损伤本构方程并优化材料常数,建立了平面应力损伤本构方程,通过分析7075铝合金在不同温度时成形极限曲线(FLC)的特点,得出不同应力状态对损伤的影响,预测7075-T6铝合金板材在四组温度和三组应变率下的FLC。研究结果表明,基于单轴损伤本构方程进行数值分析得到的应力-应变曲线与试验曲线基本吻合。应用平面应力黏塑性损伤本构方程能够预测铝合金板材热冲压过程中不同温度和应变率的FLD,为铝合金板材热冲压过程提供失效判断依据。

In view of the limitation of the Forming Limit Diagram （FLD）, which is used to evaluate the formability of AA7075 under hot stamping conditions, the continuum damage mechanics was introduced into the prediction of the FLD. A set of uniaxial damage constitutive equations was presented and the material constants were optimized. Based on the analysis of the features of Forming Limit Curves （FLCs） for AA7075 at different temperatures, a plane-stress damage equation was proposed to take account of the damage of material at different stress-strain state. Then the FLCs were predicted on the condition of four sets of temperatures and three sets of strain rates. The results indicate that the stress-strain curves of the numerical analysis of uniaxial damage constitutive equation and the experimental curves are basically consistent. Using the plane-stress unified viscoplastie damage constitutive equations can predict the FLD at different temperature and strain rate in the hot stamping process and provide the failure criteria.