Characterizing the damage behavior of thin sheets for fuselage based on in situ corrosion fatigue test and digital image correlation technique

Abstract

The effect of salt spray and salt solution on the fatigue properties of 2024-T3 aluminum alloy plate used for aircraft fuselage structure have been investigated by combining Digital Image Correlation (DIC) technology with in-situ corrosion fatigue test. For this purpose, an in-situ corrosion fatigue platform was designed for gas and liquid phases. Fatigue experimental investigation was carried out in salt spray and salt solution environments respectively, the crack propagation process was monitored by the DIC technology and the influences of NaCl concentration on fatigue life and crack growth rate were analyzed under the two kinds of corrosive environments. Moreover, the failure mechanism is discussed based on the micro-morphology of fracture and the composition of corrosion products. Experimental results demonstrated that for the corrosion fatigue in salt spray environment, there is a competition between the hydrogen embrittlement and the crack tip closure effect caused by corrosion products, which results in fatigue life decreasing with the increase of NaCl concentration first and then increasing. The fatigue life (with 3.50 wt.% NaCl salt spray) is the lowest, which is 82.9% of that in air, while the fatigue life (with 5.00 wt.% NaCl salt spray) is 112.6% of that in air. But for the corrosion fatigue in the NaCl salt solution environment, there is no obvious crack tip closure effect. In the 5.00 wt.% NaCl salt solution environment, fatigue life is 74.2% of that in air. The microfractures and strain nephogram of specimens revealed the stress concentration caused by corrosion pits, which might be the main factor for the decrease of fatigue life.