Probabilistic fracture mechanics approach accounting for both the variability of load spectra and of structural properties

In the design phase of aircraft structures, the fleet reliability should be evaluated accounting for both the variability of load spectra and of structural properties. For reliability life evaluation, a durability test under three individual load spectra is conducted for the specimens of TA15M titanium alloys stimulating the aircraft structure details. The lead crack growth (a,t) data are obtained. As a result, the equivalent initial flaw size (EIFS) values are back-extrapolated. Statistical analysis demonstrates that the variability of load spectra has no obvious influence on the EIFS distribution. The general EIFS distribution parameters are subsequently estimated. A log-normal random variable model is derived analytically to describe the crack growth rule accounting for the variability of load spectra and pertinent parameter estimation method is given, upon which the probability of crack exceedance is derived and the extent of damage is evaluated. Consequently, a probabilistic fracture mechanics approach (PFMA) is developed accounting for both the variability of load spectra and of structural properties.