Probabilities of occurrence and detection of damage in airframe materials

Abstract

The reliability of airworthiness assessment and the effective management of ageing fleets of aircraft depend critically on the quality of tools for predicting damage nucleation and accumulation and its detection, i.e. on the interrelationship between the probabilities of occurrence and detection. To illustrate these interrelationships, a mechanistically based probability approach involving localized pitting corrosion and subsequent fatigue cracking is presented. A probability of detection based on a typical state‐of‐the‐art technique for non‐destructive evaluation is used for comparison and probabilistic assessment. The results suggest that the probability of detection is inadequate, and information on damage size should be included as part of an effective airworthiness assurance methodology. An appropriate target for detecting and sizing damage of ≈ 0.10 mm with a probability of detection and a confidence level of at least 90% is suggested, versus the current capability of 1.27 mm at only 50%

Probabilistic analysis of multi-site damage in aircraft fuselages

“…The uncertainties in distribution and detection of MSD cracks in aging aircrafts necessitate modeling the crack initiation period by using probabilistic procedures. Various approaches, including pitting corrosion [18] and fretting fatigue [24] can be found in the literature. Probabilities of crack initiation have been obtained from experimental investigations [2], where the number of cycles to reach a certain crack length is determined.…”

“…In other words, methods of computational stochastic mechanics have to be applied. To this end, several authors proposed probabilistic mechanical models [16][17][18][19][20][21]. However, most of them deal with simplified models that neglect much of the effort achieved so far in deterministic analysis.…”

An energy approach to predict fatigue crack propagation in metals and alloys

“…Over the years research has been conducted on predicting fatigue crack nucleation, propagation, and structural life under cyclic loading for different materials both theoretically (Rice 1967;Weertman 1973;Ellyin 1997;Huang et al 1997;Paris 1998;McDowell 1999;Ritchie 1999;Yi et al 1999;Laz et al 2001;Deshpande et al 2002;Klingbeil 2003) and experimentally (Lang and Larsen 1999;Harlow and Wei 1999;Mars and Fatemi 2003;Korhonen et al 2004;Soboyejo et al 2004). However, the fundamental physical meaning of fatigue crack nucleation and propagation is still not resolved and requires further research.…”

A continuum damage mechanics model for pit-to-crack transition in AA2024-T3

“…Therefore, appropriate time and length scales must be considered to address the competition between time-dependent corrosion damage and cycle-dependent fatigue damage. The fracture mechanics approach outlined by Kondo [16] and Wei et al [17,[21][22][23]30,31] includes both time and length scales by introducing frequency of fatigue loading (f) and pit length (a) into the formulations. For a comprehensive discussion on the role of time and length scales in CF damage readers may refer to reference [34].…”

“…We briefly review some of the works pertinent to our discussion. A voluminous number of works treat pit-to-crack transition as a fracture mechanics problem by bringing into picture the role of stress intensity factor at the pit front [15][16][17][21][22][23][24][25][26][27][28][29][30]. To elaborate more, Wei [30] proposed two criteria required for transition of a corrosion pit to fatigue crack: (1) the stress intensity factor range ( K) for pit must exceed the threshold stress intensity factor for an equivalent crack (i.e.…”