Prediction of Optimum Spectrum for Full Scale Fatigue Test

Abstract

The standard FALSTAFF flight load sequence was modified by eliminating different levels of small amplitude load excursions to derive several different test load sequences. The fatigue crack growth behavior under all these spectrum load sequences were predicted in a compact tension (CT) specimen of an airframe grade structural steel. Crack growth predictions were made using a fatigue crack growth law derived from constant amplitude fatigue crack growth tests, which incorporated crack closure effects. It was observed that fatigue tests could be accelerated by using one of the derived optimum test load sequences without any significant effects of omitted load cycles on fatigue damage accumulation in the material. The underlying mechanism for the observed growth behavior is highlighted