Decoupling of corrosion and fatigue

A number of independent studies have shown that although pitting corrosion may occur in aircraft structures, it usually occurs on the ground and therefore does not accelerate fatigue crack growth that occurs in flight and, as such, these two phenomena are “decoupled”. To investigate this hypothesis, an experimental test program was conducted and a number of aluminium coupons were exposed intermittently to a corrosive environment and fatigued in a laboratory. The results, when compared to a baseline test coupon that was not subjected to intermittent corrosion, showed little corrosion-fatigue interaction. This substantiates previous test results from studies performed at DST Group that, for high performance combat aircraft, there appears to be little interaction between any corrosion occurring on the ground and any fatigue crack growth in flight. Since the fatigue crack growth is independent of corrosion the growth rate of the cracks can be captured well by the Hartman-Schijve equation, which has been the case as shown in previous work on fatigue cracking that had not been exposed to corrosive conditions.