Analysis of fatigue crack growth in a helicopter component

The aerospace industry is now beginning to adopt Additive Manufacturing (AM) both for new aircraft design and to help improve aircraft availability (aircraft sustainment). However, MIL-STD 1530 highlights that to certify airworthiness the operational life of the airframe must be determined by a damage tolerance analysis. MIL-STD 1530 also states that in this process the role of testing is merely to validate or correct the analysis. Consequently, if AM produced parts are to be used as load carrying members it is important that the da/dN versus ΔK curves be determined and, if possible, a valid mathematical representation determined. In this context it has recently been shown that for AM materials the da/dN versus ΔK curves can be represented reasonably well by the Hartman-Schijve (HS) variant of the NASGRO crack growth equation. This paper builds on these findings to show the HS equation can be used to accurately compute fatigue crack growth in a helicopter airframe component subjected to an industry standard flight load spectra. This finding raises the possibility to use the HS equation to assess the potential for using AM replacement parts for operational helicopters.