The Early Detection of Fatigue Damage by Exoelectron Emission and Acoustic Emission

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The paper describes the development of nondestructive test methods capable of determining the extent of fatigue damage and providing a means of predicting the future safe life of aerospace materials and structures. The fatigue process of 1100-0 aluminum was studied by means of exoelectron emission and acoustic emission measurements. The exoelectron observations were made in both vacuum and air. The exoelectron emission measurement in vacuum was accomplished by counting the emission events for selected time intervals. The measurements in air were performed using a specially developed current-measuring system with a resolution of 10-15 A. The acoustic emission measurement in air was based on the number of acoustic events occurring in selected time intervals during fatigue. The exoelectron emission curves exhibited an early rapid rise and fall of emission intensity, and again a rapid rise near the end of the test. The initial emission decrease coincided with metallurgically observed chang

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