Development of fatigue life monitoring of RMAF fighter airplanes

Abstract

The Royal Malaysian Airforce (RMAF) operates fighter squadrons of F/A-18D, MiG-29, and Sukhoi-30 which were designed on Safe Life principle. RMAF has been conducting an intensive fatigue life monitoring program to the RMAF F/A-18D and is developing fatigue life monitoring (FLM) program to other fighters in its inventory. For this purpose, RMAF MiG-29 became the focus of the development and research. The fatigue life of MiG-29 was decided to be based on the wingfuselage lug joint structure. Low Cycle Fatigue (LCF) approach was adopted. The stress spectra of the wing-fuselage lug joint, was derived through mapping of g-spectra to the 1-g stress level of the lug. The g-history was obtained from the accelerator installed in the airplane. The 1-g stress level was obtained by finite element modeling of the wing structure and lug joints using NASTRAN. Cycle counting was obtained by using rainflow procedure. Hardness and chemical composition tests combined with empirical approach were then employed for developing strain-cycle diagrams. Notched effect was taken into account using Neuber theory. Mean stress effect was dealt with using Smith-Watson- Topper formula. Miner's rule was used to calculate the fatigue damage accumulation. A fatigue life prediction software which incorporates the above concepts had been developed. The software is ready and can be used for the FLM of the RMAF MiG-29. The methodology used in the development of the fatigue life monitoring is also applicable to other Safe Life designed airplanes and becomes part of the RMAF effort in its Aircraft Structural Integrity Program (ASIP). © Springer Science+Business Media B.V. 2009.