Crack growth behavior in preloaded metallic nested-angle plates under flight load spectrum

Abstract

Numerical and experimental results are presented from a project aimed at predicting the fatigue life of a rotorcraft airframe component subjected to flight load spectrum. The airframe component is a riveted joint used on cabin frame cap splices of several civilian and military helicopters which hereafter is modeled as lap-joined nested-angle plates. This component is fatigue sensitive due to the highly cyclic and vibratory rotorcraft mission spectrum and as such prediction of its fatigue life is an important part of the design cycle. This paper presents a systematic approach that combines 3D finite element simulation in ABAQUS and 2D damage analysis in NASGRO to estimate the life of the component. In the numerical analysis, fatigue crack growth rates for through-the-thickness crack initiating from fastener holes is computed using 2D standard and weight function models with the crack plane stress field obtained from 3D FEA analysis. Effect of load interaction due to tensile overload is included using strip-yield retardation model. Finally, results of the numerical simulations are compared with representative experimental data obtained under similar spectrum loading condition.