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。
The work done in the formation of plastic zone at the crack tip has been evaluated with a simplified dislocation model and then the critical crack extension force may be calculated. Under various types of deformation, the magnitudes of work done in the plastic zone formation are different due to their different stress distributions at the crack tip. In view of the abovementioned approaches and of consideration of the correlation between K_(Ⅰc) and K_(Ⅱc) for a small scale yielding material, it has come to the conclusion: IK_(Ⅱc)>K_(Ⅰc), which is consistent in the experimental results. The ratio K_(Ⅱc)/K_(Ⅰc) and the temperature dependence of the mechanical properties of materials have been also discussed.
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