A crack growth–based individual aircraft monitoring method utilising a damage metric

The need and benefits of individual aircraft fatigue monitoring are now well established. There are broadly two fatigue damage methods employed for this purpose, namely, crack growth and stress (or strain)-life. The crack growth methods tend to provide a relative comparison between an aircraft’s usage and a baseline usage, while the strain-life methods provide a measure of the amount of fatigue life consumed against that (generally) demonstrated through a fatigue test. In this article, a new crack growth–based tracking method is described that also includes a measure of the certified fatigue life consumed. The damage model is compared against the results of an extensive coupon fatigue test programme for aluminium alloy 7050-T7451.