本文从裂纹顶端位错运动的简化模型估计形成塑性区所消耗的功;从而计算临界裂纹扩展力。由于Ⅰ型加载和Ⅱ型加载的应力状态有所不同,裂纹顶端塑性功耗也会不一样。基于上述思想,考虑了小范围屈服的K_(Ⅰc)和K_(Ⅱc)的关系,得出K(Ⅱc)>K(Ⅰc)的结论,符合实验结果;并就K(Ⅱc)/K(Ⅰc)的比值与材料性能和温度的关系作了讨论。 In this paper, a simplified model of dislocation motion at the tip of the crack is used to estimate the work done to form the plastic zone. The critical crack propagation force is then calculated. Due to the different stress states of Type I and Type II loads, the plastic power consumption at the crack tip will be different. Based on the above thought, the conclusion of K (Ⅱc)> K (Ⅰc) is obtained considering the relationship between K_ (Ⅰc) and K_ (Ⅱc) ) Ratio and the relationship between material properties and temperature are discussed.