Effect of initial defect distribution on accuracy of predicting aircraft probability of failure

Abstract

We describe the effect of the equivalent pre-crack size (EPS) distribution errors on probability of failure (PF) of an FA/18 bulkhead. We distinguish two types of errors: (1) measurement errors of the EPS distribution parameters and (2) errors that arise because PF is typically calculated based on an EPS distribution with an infinite tail, while in a flying aircraft the tail cannot be unbounded. Our results indicate that both errors have a pronounced effect on accuracy of predicted PF. We also show that because predictions of the evolving crack sizes are less sensitive to the EPS distribution errors, they could be used as a complementary measure for estimating accumulated aircraft fatigue damage.

Improved Estimation of Aircraft Probability of Failure

“…Under the applied loading spectra of interest with maximum spectra load a (defined by the International Follow-On structural test project (IFOTP) [12]), the experimental data [11] show that the crack growth behavior can be accurately represented by the Frost-Dugdale model [13]:…”

“…The extreme stress distribution parameters are co= 0.207 Mpa 1 and p = 262.2 Mpa. The critical stress intensity factor is described by a normal distribution, with m = 30 Mpa m1/2 and ok = 2 12 Mpa ml .…”

“…= yScr fneKfs(s)fK(K)dsdK (12) where fK (K) and fs (s) are given by equations (2) The upper limit of one of the integrals in the expression (12) is determined from the expression (10): Crack length, mm can be extended by about 700 flight hours. While this effect is not as significant as the one due to truncating the EPS distribution by a maximum defect, it does indicate that updating the prior crack distribution leads to extending the service life, which may be important for economic and operational considerations.…”