Pulsed Eddy Current Inspections of Aircraft Structures in Support of Holistic Damage Tolerance

Riveted fuselage splice joints are a common feature in the construction of transport aircraft. Traditional durability and damage tolerance analyses of these joints have often ignored or greatly simplified the effect of corrosion damage and its interaction with fatigue. This has required that corrosion damage be repaired as soon as it is detected, which has in turn discouraged the use of sensitive nondestructive inspection (NDI) techniques which may find structurally insignificant amounts of damage. New holistic life assessment models which do account for corrosion damage are under development by many research groups including the National Research Council Canada. These models require quantitative assessment of corrosion damage as well as fatigue damage.

Pulsed eddy current (PEC) inspection methods have been developed to address these needs, and this paper presents the results of a signal processing technique developed to characterize material loss in a two-layer structure from PEC data. The goal of the technique is to map the thickness of both the 1st and 2nd layers. Applying this method to PEC data measured on a laboratory test specimen shows that corrosion can be quantified with an error of less than 4% of a layer thickness.

The effect of NDI error in corrosion quantification on maintenance and repair is estimated using a holistic, probabilistic life assessment model. The paper will discuss how these models, along with verified NDI techniques, can be used to implement new proactive maintenance paradigms for aircraft structural components.