A novel accelerated fatigue test method of mission synthesis considering the segmented S-N curve

Abstract

The vibration excitation in extreme environments poses severe challenges to the fatigue life of aviation equipment. Although the accelerated fatigue test applying fatigue damage spectrum (FDS) is effective in predicting the fatigue life of critical components under a real operating environment, the life prediction error for the materials with segmented S-N curves may exceed orders of magnitude. Therefore, an improved FDS considering the segmented S-N curves is proposed, and the segmented integral reconstructed FDS formulas are applied to solve the synthetic spectrum for accelerated fatigue tests. Through substantial simulations and tests of the L-shaped beam under different spectrums and vibration directions, the prediction errors calculated by narrowband and wideband methods are less than 24.3 % and −16.2 %, respectively, better than the traditional FDS with errors up to 748 %. When the 6061-T6 S-N curve is fitted by two straight lines in the double logarithmic coordinate system, the best fitting segmented position is 10^4.8s with the high accuracy of predicted fatigue life. For uniaxial and multiaxial random vibration, even if the bandwidth characteristics affect the prediction life, the fatigue life predicted by the improved FDS is always within the life region of the different spectral moment synthesis approaches by the wideband method.