C-Mn钢裂尖区解理断裂行为的研究

Study of fracture behavior at crack tip within C-Mn steel

对C Mn钢三点弯曲裂纹试样进行了实验和有限元计算,分析了裂尖断裂行为.研究结果表明:在达到某一临界载荷前,裂尖只发生简单的钝化,并且在裂尖前端满足解理断裂三个判据的不同区域是相互分离的.因此形核的裂纹因不能扩展而不能引发解理断裂.随外载荷增加,高于这个临界载荷时,小裂纹在裂尖处形核、扩展,随后被钝化.此时裂尖前端的塑性应变被保留下来,但是三向应力度被释放掉,随后又重新建立,从而使得三个区域相互靠近.在第二个临界载荷下,三个判据都满足的区域相互重叠,解理裂纹形核并扩展.可以在裂纹形核区域和裂纹扩展区域刚要重叠的那一瞬时,决定解理断裂的最小距离.结合解理断裂的三个判据,裂尖断裂行为及由其产生的断裂驱动力参数(εp,σm/σe和σyy)的相应变化为钢的解理断裂在细观上提供了一个完整的物理模型.

The fracture behavior at crack tip within CMn steel is analyzed based on the experiments of 3 PB precracked specimens and FEM calculation and simulation. The results show that before a critical load is reached, the crack tip is blunted only and in its vicinity the three criteria of cleavage fracture are satisfied in different regions separated from each other. The nucleated cracks cannot propagate and the cleavage fracture cannot be triggered. With the applied load increasing higher than this critical load, a short crack is initiated and extended at the precrack tip and then is blunted again. While the plastic strain remains in front of the tip, the stress triaxiality is released and then rebuilt. Under the second critical load, the regions, where the three criteria are satisfied, are overlapped each other and cleavage crack is nucleated and propagates. The minimum distance for cleavage fracture is that on where the overlapping of abovementioned regions begins. Combined with the three criteria previously mentional, the fracture behavior at crack tip and the corresponding changes of driving forces (εp,σm/σe and σyy) provide a complete physical model of cleavage fracture of steels on a local scale.