剪切修正GTN模型在小冲杆试验中的应用研究

小冲杆试验作为一种非标准的微试样测试技术，能有效地获取薄板结构的材料参数。而选用合适的损伤模型对准确表征材料变形到断裂的整个过程有着重要影响。基于NAHSHON提出的含剪切修正项的Gurson-Tvergaard-Needleman(GTN)模型，通过有限元软件ABAQUS及用户自定义子程序VUMAT考察不同应力三轴度对断裂失效的影响。采用有限元模拟和拉伸试验获得冷轧硅钢材料的无损伤弹塑性力学参数以及GTN损伤演化模型中的形核参数和临界断裂参数，通过纯剪切试验和数值模拟的对比确定出材料中微孔洞的剪切变形对材料损伤演化的贡献。运用剪切修正的GTN模型对小冲杆试验进行模拟，结果表明，由于修正GTN模型考虑了微孔洞剪切畸变的对材料损伤影响，模拟结果比原GTN模型更接近于试验数据，可更好地应用于小冲杆试验的研究。

Study on the Application of Shear Modified GTN Model to Small Punch Test

As an important non-standard test technology, the testing result of small punch test(SPT) is largely influenced by the experiment condition. In the research of SPT, an appropriate mechanical constitutive model of material is much needed. The shear modified GTN model proposed by NAHSHON is implemented into ABAQUS via user defined material subroutine VUMAT to study the material fracture behavior at various stress triaxialities. The undamaged elastic-plastic mechanical properties of the cold rolled silicon steel are obtained by the tensile test. The damage evolution parameters of void nucleation are determined by experiment data of tensile test combined with a large number of simulations. The shear modified parameter that characterizes the contribution of void distortion to damage evolution is identified by the comparison of the results of pure shear test simulations and the experiment data. The shear modified GTN model is used to simulate the small punch test. The results show that, as the void distortion is taken into account in damage evolution, the prediction results of the shear modified GTN model is much more consistent with experiment data than the original GTN model. It comes to the conclusion that the shear modified GTN model can reveal the failure mechanism of material better in intrinsic, and is a better choice to apply in the study of small punch test.