Management of Airframe In-Service Pitting Corrosion by Decoupling Fatigue and Environment

Abstract

Corrosion-induced maintenance is a significant cost driver and availability degrader for aircraft structures. Although well-established analyses enable assessing the corrosion impact on structural integrity, this is not the case for fatigue nucleation and crack growth. This forces fleet managers to directly address detected corrosion to maintain flight safety. Corrosion damage occurs despite protection systems, which inevitably degrade. In particular, pitting corrosion is a common potential source of fatigue. Corrosion pits are discontinuities whose metrics can be used to predict the impact on the fatigue lives of structural components. However, a damage tolerance (DT) approach would be more useful and flexible. A potential hindrance to DT has been the assumption that corrosion-induced fatigue nucleation transitions to corrosion fatigue, about which little is known for service environments. Fortunately, several sources indicate that corrosion fatigue is rare for aircraft, and corrosion is largely confined to ground situations because aircraft generally fly at altitudes with low temperature and humidity Thus, it is reasonable to propose the decoupling of corrosion from the in-flight dynamic (fatigue) loading. This paper presents information to support this proposition, and provides an example of how a DT approach can allow deferring corrosion maintenance to a more opportune time.

Computing the durability of WAAM 18Ni 250 maraging steel specimens

“…A view of the failure surface is also shown in Figure 6. The fatigue surface was essentially Mode I and, as such, resembled those seen in previous papers 24,32,[39][40][41][42] for Mode I fatigue crack growth in materials that ranged from bridge steels to the highstrength aerospace quality aluminum alloys AA7075-T7351 and AA7050-T7451. As a result, as we will see in the next section, the growth of this naturally occurring crack is consistent with the exponential crack growth histories associated with the growth of naturally occurring sub millimeters cracks seen in both RAAF and USAF aircraft.…”

Modeling Metallic Fatigue Data Using the Birnbaum–Saunders Distribution

“…Traditionally, these areas have often utilized lognormal or Weibull distributions [44]. Furthermore, considering the effects of environmental factors such as corrosion, as discussed in [45,46], could enrich the predictive capabilities of these models. These types of studies could offer a more comprehensive insight into fatigue and fracture in working conditions where accurate predictions are essential for the maintenance and safety of mechanical systems.…”