钢板拉伸颈缩致断裂的应变局部化过程

Strain localization process of steel plate in tensile from necking to fracture

利用MTS810实验机和Zwick HTM5020高速拉伸实验机对钢板进行不同应变率加载下的拉伸实验。利用数字图像相关性方法 (Digital Image Correlation,DIC)对拉伸过程中试件表面的应变场进行分析,得到标距段和颈缩区两个区域沿拉伸方向的平均应变历史曲线,其结果显示两曲线的分离时刻即为非局部化颈缩起始点;该分离时刻点与准静态下的Considere判据和动态下的Batra理论得到的颈缩点一致。DIC分析云图形象的显示了试样拉伸过程中从颈缩开始致断裂的应变局部化演化过程。提取云图中典型位置的应变分布曲线,获得不同时刻相同位置的真应变大小。此外,试样的局部断裂应变随应变率的增加而增大。

The tensile tests with different strain rates of steel sheet were carried out on MTS810 and Zwick HTM5020 mechanical simulator.Digital image correlation(DIC)was used to analyze the strain field on the surface of the specimen during the stretching processes,and the average strain history curves along the tensile direction of gauge section and necking area were obtained.The results show that the separation moment of the two curves is the onset of non-localized necking.The separation moment point is consistent with the onset non-localized necking obtained via Considere criterion in quasi-static tension and the Batra theory in dynamic tension.The strain maps got from DIC show the evolutionary processes of the localization of strain from necking to fracture in the tensile process of specimens.The strain distribution curves in typical position were extracted from strain maps to obtain the true strain of neck area in the same position and different moments.Moreover,the localized fracture strain of specimens increases with the increase of strain rate.