中文摘要：

为分析不同材料和尺寸的薄板试样在室温下拉伸破坏后均形成与横截面夹角在20°～25°之间斜断口的原因，首先用统计方法对试样内随机分布微缺陷进行讨论，提出一种在宏观尺度上材料内微缺陷分布局部非均匀简化模型的假设．应用含孔材料损伤本构模型对含有不同方向微缺陷分布局部非均匀薄带区域的16MnNb薄板试样变形至破坏全过程进行数值模拟．结果表明，斜断口形成主要是由于试样内在与横截面夹角小于45°的带形区域内微缺陷分布局部非均匀造成，且与该带形区域在试样中位置无关；由于考虑微缺陷分布局部非均匀，得到试样的斜断口形成过程与试验现象完全一致；同时结合试验断口形貌，对变形过程中颈缩截面内损伤演化和破坏过程进行研究，进一步解释薄板试样的损伤破坏机制．

英文摘要：

It is observed from the experiments that the angle between the fracture section and the cross section of thin plate specimens under the axial tension is always in the range of 20 to 25 degree. To analyze its formation mechanism, the statistic characteristic of the random distribution microdefects in the thin plate specimens was studied firstly. A local non-uniformed distribution model of the microdefects in the thin plate specimens was proposed. Based on this model, Gurson model modified by Tvergaard and Needleman （GTN model） was employed to simulate the deformation and rupture procedure of the plate specimens under the axial tension load. The results show that the local non-uniformed model of the microdefects is reasonable. The slanted fracture section is formed because the small microdefects non-uniformed distribution band region exists in the thin sheet specimens, whose angle with the cross section is beyond 45 degree. The location of the non-uniformed band in the specimens has little influence on the formation of the slanted fracture. The numerical simulation of the rupture procedure for the thin plate specimens based on the model proposed is identical with the fracture phenomenon from the experiments. At the same time, according to the fractography from the scanning electron microscope （SEM）, the damage evolution and fracture process were investigated. On the base of these results, the damage behavior and fracture mechanism of the thin plate specimens were further explained.