数字图像相关法在薄板成形极限测定中的应用

Digital image correlation in determination of forming limit diagrams for sheet metal

成形极限曲线可展现板料在塑性失稳前所能达到的最大变形程度,是板料成形分析中的重要判据。为获得准确的试验成形极限曲线,该文通过刚性半球凸模胀形试验、采用数字散斑图像相关方法对AA6061铝板的成形极限曲线进行测定,得出了成形极限试验测定和极限应变提取的方法;通过对AA6061铝板进行盒形件拉深试验,建立拉深过程的有限元模型,比较了数值模拟和试验测定的极限拉深深度。比较结果表明,数字图像相关方法能够有效获取变形过程中的全场应变信息、搜索临界破裂状态,且能采用曲线拟合方式计算极限应变,避免了人为误差,提高了测量精度。拉深试验表明,所测成形极限曲线对拉深极限具有较高的预测精度。

Forming limit curve is used to describe the formability of metallic sheet before plastic instability ,which is an important material property .Rigid hemisphere punch bulging test for AA6061 aluminum alloy was performed with a three dimensional digit‐al speckle correlation strain measuring system ,a method of performing forming limit experiment and processing limit strain is giv‐en .Also ,the experiments and numerical simulation of box part deep drawing for AA6061 were performed ,then the limit drawing heights of them were compared .The results show that ：the digital speckle correlation is able to capture the whole strain field . The suggested method could better search the critical fracture condition ,and the curve fitting method is used to capture the limit strain ,which improves the measuring accuracy without artificial selection of critical point .The verification of deep drawing test shows that the obtained forming limit curves can give a higher prediction accuracy for drawing fracture .