The Early Detection of Fatigue Damage
Abstract
The report describes the continuing effort to develop 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. During the report period, the fatigue process in 1100-O aluminum was studied by means of exoelectron emission and acoustic emission measurements. The exoelectron observations were by means of measuring the current produced by fatigue damage in air; the acoustic emission measurement was based on the number of acoustic events occurring in selected time intervals during fatigue. It appears that there is a trend indicative of a stress-independent relationship between the change of exoelectron emission current and the percentage of the spent fatigue life based on the current after a selected number of cycles. The intensity of acoustic emission was shown to increase or decrease by orders of magnitude during the fatigue life. The first significant change of acoustic emission was apparently correlatable to 8 to 20 percent of the specimen fatigue life. The continuing metallographic examination confirmed that surface slip striations appear very early in the fatigue process and appear to directly correlate with the exoelectron emission phenomenon.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 30, 1970
- Accession Number
- AD0715630
Entities
People
- D. S. Weinstein
- F. M. Coate
- J. F. Moore
- S. Tsang
- Sean Hoenig