GTN损伤模型对C-Mn钢缺口拉伸试样延性断裂的预测

PREDICTION OF DUCTILE FRACTURE IN TENSILE SPECIMENS WITH NOTCHES FOR A C-Mn STEEL BY USING GTN DAMAGE MODEL

用GTN(Gurson,Tvergaard,Needleman)损伤模型对不同缺口根半径的C-Mn钢缺口圆棒拉伸试样的延性断裂进行有限元模拟预测。结果表明,当缺口根半径R≤2 mm时,GTN模型对缺口拉伸时的最大载荷Pm、起裂载荷Pi、断裂载荷Pf和断裂功E的预测值与实验值较为接近。而当R>2 mm后,预测值与实验值的偏差变大。其原因在于GTN模型是基于微孔洞长大和聚合的延性断裂机理而建立,对于根半径较小,促使孔洞长大的三向应力度较高的缺口试样较为适用。GTN模型预测的三个特征载荷,尤其是表征韧性的断裂功E的值总体上高于实验测定值,并且其预测的延性起裂位置在R≥1 mm时也与实验观察不一致。其原因是GTN模型未考虑实际材料组织中具体的夹杂物/孔洞的尺寸、形态、分布和方位对损伤演化和断裂过程的影响。

The ductile fracture in tensile specimens with various notch root radiuses for a C-Mn steel has been predicted by using GTN （Gurson, Tvergaard, Needleman） damage model. The results show that, in the case of notch radius R ≤2 mm, the prediction values of the maximum load Pm, fracture initiation load Pi, fracture load Pf and fracture work E are close to the experimental values. But in the case of R 〉 2 mm, the difference between the prediction and experimental values becomes large. The reason for this is that GTN model is based on the ductile failure mechanism of void growth and coalescence, and it is suitable for the specimens with small notch radius that has high stress triaxiality for void growth. The values of GTN model prediction for the three characteristic loads, especially for the fracture work E characterizing toughness are generally higher than the experimental values. And also the prediction for the fracture initiation locations is not consistent with the experimental observation in the case of R ≥ 1 mm. The reasons for these are that the effects of the size, morphology, distribution and orientation of the inclusions/voids on the damage evolution and fracture process have not been considered in the GTN model.