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.