裂纹深度对裂尖应力分布及韧性的影响

The Effect of Precrack-Depth on the Stress Distribution Ahead of the Crack Tip and Fracture Toughness

对C-Mn钢不同裂纹深度试样的有限元分析及力学实验的结果表明,在未出现延性裂纹的下转变区(-100℃),临界COD值δ_c随裂深度的增加而降低,在相同裂尖张开值时,浅裂纹裂端的三轴应力度明显低于深裂纹,表现为δ_c明显依赖于三轴应力度。解理的临界阶段为第二相尺寸的微裂纹向周围基体扩展的应力控制过程,为使裂端主应力提升至相同水平(δ_f),浅裂纹需要更大的裂尖张开值,这是浅裂纹试样具有较高韧性的内在原因。

The fracture toughness test and finite element analysis have been carried out on the precracked bending specimens with various crack depth in C-Mn steel and the following conclusion could be drawn. In the lower transition region (about -100℃) without the extension of ductile crack, the critical value of COD decreases with the increase of precrach depth. At the same value of COD, the triaxiality of stress ahead of a shallow crack is remarkably lower than that of the deep one, i. e, the critical COD having a relationship with the triaxality of stress. The critical process of cleavage is whether the principal stress is large enough to propagate a second phase particle-aized microcrack into the surrounding matrix. To raise the principal stress ahead shallow crack needs a large crack opening displacement compared with the deep one, therehy the shallow crack specimen having a higher fracture toughness