The Effect of Decoupling of Corrosion and Fatigue

摘要

Several independent studies have shown that although pitting corrosion may occur in aircraft structures, it usually occurs while an aircraft is on the ground. This raises the prospect that any such corrosion therefore does not accelerate fatigue crack growth that occurs in flight and, these two phenomena are "decoupled". To investigate this hypothesis, an experimental test program was carried out to study the effect of environment on fatigue crack growth and crack surface appearance that alternating moisture exposure during the life of a crack could produce. The tests focussed on simulating an intermittent moist environmental exposure due to condensation typical of what may be expected to be found in internal structures while an aircraft is on ground, with its effect on fatigue crack growth from in-flight loading where the environment is expected to be dry and the water is likely to have evaporated. The results were analysed using the Hartman-Schijve variant of the NASGRO equation and this equation was found to simulate the resulting crack growth curves well.