微观裂纹尺寸ι_0的确定及其对门槛应力强度因子的影响

The Influence of Microcracks on the Threshold Stress Intensity Factor

本文首先给出名义小裂纹尺寸的定义，并详细地分析过渡区域内门槛应力强度因子的变化．本文假定当外加应力达到疲劳极限时，裂尖处塑性区尺寸大小等于某一材料常数，并认为这一材料常数是晶粒尺寸大小，从而建立起晶粒尺寸、疲劳极限、屈服极限、微观裂纹尺寸四者之间的关系。然后通过名义小裂纹的定义推导出晶粒尺寸、屈服极限、门槛应力强度因子三者之间的关系。最后，用导出的公式计算晶粒尺寸并与实验结果对比，结果表明所导出的公式可靠，可用于工程计算。

In this paper, the nominal crack length was defined, and the variation of the threshold stress intensity factor in the transition zone was analysed in detail. Based on the assumption that the plastic zone at crack tip is equal to the grain size when external stresses approach fatigue limit, the relationship among grain size, microcrack length, fatigue limit,yield strength and threshold stress intensity factor was derived. The results given by the formulae in this paper have been compared with experimental data.