飞机结构疲劳寿命分散系数研究

ON FATIGUE LIFE SCATTER FACTOR FOR THE AIRCRAFT STRUCTURE

飞机结构疲劳寿命分散系数是飞机疲劳寿命评定工作中的一个重要可靠性指标。目前,我国飞机定寿工作中采用全机疲劳试验总试验小时除以疲劳寿命分散系数得出机群安全寿命的结论。通常,在不考虑机群服役环境差异而导致的环境分散系数时,所选取的疲劳寿命分散系数主要考虑两部分,一是机群使用载荷差异导致的载荷分散系数,二是结构材料与制造质量差异导致的结构分散系数。介绍分析了服从对数正态分布与威布尔分布时飞机结构疲劳寿命分散系数的表达形式;对于同型飞机结构疲劳寿命在不同载荷谱下服从对数正态分布的情况,推导了疲劳寿命分散系数可用载荷分散系数与结构分散系数乘积表示的条件;对于同型飞机结构疲劳寿命在不同载荷谱下不服从同一分布的情况,通过等损伤原理可以将服役飞机实际飞行小时数折算到同一试验载荷谱条件下的当量飞行小时数,计算同一试验载荷谱下的结构分散系数,以此作为疲劳寿命分散系数求得的飞机结构安全寿命可作为单机寿命管理的基准寿命值。

The fatigue life scatter factor is an important reliability index of the assessment of aircraft fatigue life. At present, the safe-life of a fleet is gotten by using the total test hours and the fatigue scatter factor. Usually, the environment scatter factor caused by the different service environments is not considered, and the fatigue scatter factor mainly includes two parts, one is the load scatter factor caused by the load spectrum difference of fleets ; the other is the structure scatter factor caused by the difference of material and manufacturing quality. The expressions of scatter factor of fatigue life obeying the log-normal distribution and Weibull distribution are introduced and analyzed. To the situation that the structure fatigue life of the same aircraft model under different load spectrums obeys the log-normal distribution, the condition that the fatigue scatter factor is the product of the load scatter factor and the structure scatter factor is deduced. To the situation that the structure fatigue life obeys the different distributions, the service flying hours can be converted into the equivalent flying hours under the same test load spectrum based on the equal damage principle, the structure scatter factor under this spectrum can be calculated and can be taken as the fatigue life scatter factor, the safe-life calculated by this scatter factor can be seen as the reference value for the management of individual aircraft life.