中文摘要：

从瞬时裂纹长度及应力强度因子服从对数正态分布的假设出发，基于Paris裂纹扩展速率公式讨论当实验数据较少时，常幅载荷下结构元件临界裂纹长度和瞬时裂纹长度的分布特性，给出一个计算瞬时裂纹长度分布参数的方法，建立常幅载荷下结构元件断裂可靠性分析的裂纹长度模型，阐述元件断裂可靠性的分析方法。对2024-T351材料的CT（compact tension）试件试验数据分析表明，文中给出的模型是合理的，预测结果和试验结果吻合良好。

英文摘要：

The fracture toughness and the instantaneous length of fatigue crack are random variables and assumed to follow logarithmic normal distribution approximately. To the situation where few experimental data are available, a reliability model of structural components under constant amplitude loading is presented, which is based on the distribution of instantaneous crack length. The model proposed the steps for computing parameters of the Paris-Erdogan＇ s crack propagation equation and established the expectation and variance of the crack length at a given time. Consequently, a crack length-based reliability model was set up. Experimental data of CT（compact tension） test pieces made of 2024-T351 Aluminum alloy were employed to demonstrate the suitability of the model. The predicted results showed a good agreement with the experimental data.