Estimating crack growth in rotorcraft structures subjected to mission load spectrum

This paper is an extension of the work originally reported on the international conference of experimental mechanics. In this extended work, numerical and experimental results are presented from a project aimed at predicting the fatigue life of a rotorcraft structural component subjected to flight load spectrum. The structural component is a riveted joint used in cabin frame cap splices of several civilian and military helicopters modeled herein as a lap-joined nested angle assembly. This component is fatigue sensitive due to the highly cyclic and vibratory nature of a rotorcraft mission load spectrum and as such accurate prediction of its fatigue life is of major importance in the design cycle. In this work, numerical studies are conducted using constant amplitude and mission spectrum loads. The rate of fatigue crack growth for through-the-thickness crack initiated from the critical fastener hole is computed using 2D standard and weight function models with the crack plane stress field obtained from 3D finite element analysis. Effect of load interaction due to tensile overload is included using strip-yield retardation model and the effect of surface shear arising from contact friction between the plates and the fasteners is studied using parametric models. Finally, results of the numerical simulations are compared with representative experimental data obtained under similar spectrum loading condition.

► We predicted crack growth in rotorcraft structures subjected to mission spectrum.
► The numerical simulation includes effects of contact friction and bolt preloads.
► Experimentally, crack growth is measured using Meandering Winding Magnetometer.
► Nasgro’s TC13 with crack plane stress input from 3D FEA gives a good estimation.
► Inclusion of surface friction results in a highly conservative life prediction.