Nondestructive characterization of corrosion damage and fatigue life

Microradiographic and ultrasonic characterization of fatigue crack emanating from pitting corrosion is discussed. Crack initiation and growth from the artificial pit of different depths in Al-2024-T3 alloy is studied experimentally. The effect of crack closure on the radiographical and ultrasonic detection of fatigue crack is also illustrated. The experimental results were analyzed using fracture mechanics models including those for small cracks. The model shows very good agreement with experiment in describing the initial and growth of a crack emanating from a pit and in predicting the dependence of the reduction of fatigue life on pit size. Using this analysis, a relation between the depth of the corrosion pit and the fatigue life is established, and thus the prediction of fatigue life of the sample with corrosion pit can be predicted based on the radiographic and ultrasonic measurements of pit and crack sizes.

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