在低应力强度因子范围下，许多材料都表现出疲劳小裂纹扩展速率高于长疲劳裂纹扩展速率，这对于准确预报材料寿命具有很大影响。文章在统一疲劳寿命预报模型基础上，提出疲劳小裂纹扩展速率预报公式。该预报公式不但考虑了疲劳小裂纹尖端的弹塑性行为，还考虑了疲劳小裂纹阶段控制裂纹扩展的是疲劳极限，而不是控制大裂纹扩展的应力强度因子门槛值，小裂纹扩展门槛值是裂纹长度的函数。利用该预报公式计算常幅载荷下切口试件和无切口试样的疲劳小裂纹扩展速率，并对试样进行寿命预报，预报结果与试验结果吻合较好。%The observation that the short fatigue cracks grow faster than long fatigue cracks at the same nominal driving force and even grow at stress intensity factor range below the threshold value for long cracks in many materials. The anomalous behaviors of short cracks have a great influence on the accurate fatigue life prediction of marine structure. Based on the unified fatigue life prediction model developed in the authors group, a modified model of short fatigue crack propagation is pro-posed in this paper. The elastic-plastic behavior of short fatigue cracks in the vicinity of crack tips is considered in the modified model. The modified model includes that the rate of crack propagation for very short cracks is determined by the range of cyclic stress rather than the range of the intensity factor controlling the long cracks propagation. The threshold stress intensity factor range of short fa-tigue cracks is a function of crack length. The proposed model is used to calculate short cracks prop-agation rate and the corresponding fatigue life for notched specimens under constant amplitude load-ing. And the model is validated by comparing model prediction results with the experimental data.
展开▼
