Prediction of Fatigue Life by X-Ray Diffraction Methods.
Abstract
Through the use of a nondestructive X-ray method, the precrack fatigue damage in aluminum 2024-T3 has been determined. The method is based on (a) the observation that fatigue fracture is initiated when the excess dislocation density in the surface layer attains a critical value; and (b) a knowledge of the excess-dislocation/depth profile for various fractions of fatigue damage. This profile indicates that if the X-ray radiation does not penetrate sufficiently deep into the surface layer, the dislocation density measurements cannot be used as a measurement of fatigue damage. By contrast, the application of penetrating molybdenum radiation, which irradiates grains in the bulk as well as in the surface, gives rise to a linear relationship between the X-ray linewidth and fatigue damage. The slope of this line is sufficiently steep so that, with a knowledge of the critical X-ray linewidth, the fatigue damage can be predicted. The fraction of fatigue damage is given by the ratio beta/beta*, where beta is the linewidth at any number of fatigue cycles and beta* is the critical linewidth at fracture. The critical linewidth may be estimated by using X-ray radiation from chromium and/or by a multiple film technique after the specimen has been cycled approximately 20 percent of its fracture life. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1979
- Accession Number
- ADA070044
Entities
People
- I. R. Kramer
- R. N. Pangborn
- S. Weissmann