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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 crack and crack tip behavior of C Mn steel with three-point bending crack was analyzed and the fracture behavior was analyzed. The results show that only a simple passivation of crack tip occurs before a certain critical load is reached, The front end meet the three criteria of cleavage fracture in different regions are separated from each other, so the nucleation of the crack can not be extended because it can not lead to cleavage fracture with the increase in external load, higher than the critical load, the small crack at the crack tip Nucleation, expansion, followed by passivation. At this point plastic tip of the tip is retained, but the three-dimensional stress is released, and then re-established so that the three regions close to each other in the second critical load , The regions where the three criteria are satisfied overlap with each other to cleave the nucleation and propagation of the crack, and the minimum distance of cleavage fracture can be determined at the moment when the crack nucleation region and the crack propagation region just overlap each other. The three criteria of fracture, the crack tip behavior and the corresponding changes of the fracture driving force parameters (εp, σm / σe and σyy), provide a complete physical model for the cleavage fracture of the steel.