Prediction of Fatigue Life by X-Ray Diffraction Methods.
Research and development interim rept.,
DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER BETHESDA MD
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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-dislocationdepth 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 betabeta, 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 andor by a multiple film technique after the specimen has been cycled approximately 20 percent of its fracture life. Author
- Metallurgy and Metallography
- Test Facilities, Equipment and Methods