飞机机翼缘条紧固孔细节原始疲劳质量评估方法

为了对飞机机翼缘条紧固孔细节原始疲劳质量进行评估，本文首先对飞机机翼缘条结构中常用的BXXX铝合金紧固孔试件分别开展了高、中、低3种应力水平下的疲劳试验，通过断口判读和反推得到3组关于裂纹长度a和疲劳寿命t的（a?t）数据，在此基础上应用当量初始缺陷尺寸（EIFS）控制方程对每个试件的EIFS值进行计算并初步评估，验证了在不同应力水平下紧固孔结构细节的EIFS无显著性差异；得到了紧固孔结构细节的裂纹萌生时间（TTCI）分布，在指定应力水平下对紧固孔结构细节95%置信水平下的经济寿命进行预测，并与设计寿命进行对比，提出了一种不同超越概率P下的结构细节当量初始缺陷尺寸模型，基于给定5%的裂纹超越概率，对结构细节的通用EIFS分布进行评估。通过以上对飞机机翼缘条紧固孔细节原始疲劳质量的三重评估，得到综合评估结果:飞机机翼缘条紧固孔细节原始疲劳质量满足要求。 

Evaluation method of initial fatigue quality of aircraft wing flange fastener holes

On analyzing the details of kinetic links of parts and structures of aircrafts, one can find few bad links. But fastener hole is the weakest link where abnormal stress is produced and initiation of crack occurs. The initial fatigue quality of aircraft wing flange fastener is the key parameter, which affects the durability of aircraft structure. The initial fatigue quality of structural details is usually characterized by the equivalent initial defect size (EIFS) and the time to crack initiation (TTCI). To evaluate the initial fatigue quality of aircraft wing flange fastener hole details, this paper first carried out fatigue tests at high-, medium- and low-stress levels on the BXXX aluminum alloy fastener hole specimens generally used in aircraft wing flange structures, and obtained three groups of (a?t) datasets about crack length a and fatigue life t through fracture interpretation and back stepping. On this basis, the EIFS governing equation was used to evaluate the EIFS value of each specimen, and it is found out that there is no significant difference in equivalent initial flaw size under different stress levels; TTCI distribution of structural details is obtained, and the economic life of specified stress level under 95% confidence level of fastener hole structural details was predicted, and compared with the design life; a structural detail equivalent to initial flaw size model under different exceedance probability P was proposed. Based on the given 5% crack exceedance probability, the general EIFS distribution of structural details was evaluated. The comprehensive evaluation results were obtained through the above triple evaluation of the initial fatigue quality of the fastener hole details: the general EIFS distribution and the EIFS value of each test piece are less than the allowable value, and the economic life is greater than the allowable value, so the original fatigue quality of the details of the fastening holes of the aircraft flange meets the stringent requirements.