延性材料断裂准则与平面应变断裂韧度

延性材料的临界断裂规律对结构完整性评价和金属塑性成形分析具有重要意义，但相关的弹塑性断裂强度研究长期存在瓶颈。本文针对30Cr2Ni4MoV低压转子钢和3Cr13不锈钢，完成了不同应力三轴度的4类试样拉伸破坏试验，基于FAT （Finite-element-analysis Aided Testing）方法，通过有限元迭代分析实现试样的载荷-位移关系逼近，进而获得材料直至断裂的全程等效应力-应变关系，并以此通过有限元正向分析获取4种试样的临界断裂阈值和临界应力三轴度，提出了基于临界断裂单元的应力三轴度与第一主应力阈值之间的对数型断裂强度准则。结果表明，2种材料、4类试样的FAT阈值分析结果与断裂强度准则符合良好。最后，基于断裂强度准则提出了依据I型裂纹尖端的应力分布预测材料平面应变启裂断裂韧度的新方法，并获得了30Cr2Ni4MoV低压转子钢和3Cr13不锈钢的平面应变启裂断裂韧度，结合临界断裂准则和裂纹静态扩展机理，提出了I型裂纹的材料J阻力曲线的理论预测方法，并给出了30Cr材料的预测结果。

Fracture criterion and plane-strain fracture toughness of ductile materials

Research on fracture criterion has great significance in structural integrity evaluation and metal forming analysis However, research on elastic-plastic fracture strength has long been a bottleneck. In this paper, the Finite-element-analysis Aided Testing (FAT) method was used to obtain the accurate full-range effective constitutive relation up to failure of the 30Cr2Ni4MoV rotor steel and 3Cr13 stainless steel. Four typical structure failure tests of the specimens with different stress triaxiality were carried out, and their fracture thresholds and critical stress triaxiality were obtained using finite element analysis according to the full-range constitutive relations. The results show that there exists logarithmic law between the maximum stress triaxiality and the first principal stress thresholds as those representative volume elements with the triaxiality of the specimens reach their critical breaking state. According to the first principle stress envelope of crack tip and the logarithmic fracture criteria, the Ⅰ-type crack fracture toughness of 30Cr2Ni4MoV and 3Cr13 steel was predicted. A new method is proposed to predict the J-resistance curve of the material with the I-type crack fracture based on the mechanism of crack static growth. As an example, the J-resistance curve of 30Cr steel was predicted and discussed.