机群结构耐久性分析的裂纹萌生方法

为采用裂纹萌生方法(CIA)进行机群结构耐久性分析,需要综合考虑载荷谱分散和结构特性分散,但是关于综合考虑结构特性和载荷谱分散的机群寿命标准差取值应如何确定并未给出明确的方法。为此,进行了某飞机某关键结构7B04 T74铝合金模拟试件在3个单机谱下的耐久性试验,通过断口判读确定试件裂纹萌生寿命,反推得到结构细节的三参数式P-S-N曲线参数,对比分析表明载荷谱差异对P-S-N曲线参数无影响。为描述机群载荷谱分散的影响,提出了机群"当量"P-S-N曲线的概念和参数估计方法。采用疲劳分析方法确定细节裂纹超越概率,对损伤度进行评估,建立了综合考虑结构特性分散和载荷谱分散的CIA。

Crack initiation approach for durability analysis on aircraft structures of a fleet

The variability of structural properties and load spectra should be accounted for to evaluate the durability life for a fleet by the crack initiation approach (CIA), but the method to determine the life standard deviation considering the variability of structural properties and load spectra is not clear. Therefore, a durability test was conducted for the specimens of 7B04 T74 aluminum alloys stimulating the structure details of a fighter under three individual load spectra of a fleet, from which the lead crack growth data have been observed in fractograph. As a result, the parameters of P-S-N curve for this structural detail are back-extrapolated. Statistical analysis shows that the variability of load spectra has no obvious influence on the P-S-N parameters corresponding to those three load spectra. An equivalent P-S-N curve and parameter estimated method have been presented to describe the influence of load spectra in a fleet. The probability of crack exceedance is derived and the extent of damage is evaluated. Consequently, a CIA is developed accounting for both the variability of load spectra and of structural properties.