STUDY OF BRITTLE CRACK PROPAGATION.
Final summary rept. Feb 68-Feb 69,
MARTIN MARIETTA CORP DENVER COLO DENVER DIV
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The surface layer stresses of copper, titanium, and 7075-T6 aluminum were measured. The rates of the relaxation of the surface layer stress of copper and the titanium alloys were also determined. A critical experiment was performed showing that cyclic work hardening is caused by an increase in the surface layer stress. When copper and aluminum specimens work hardened instead of work softening. The role of the surface layer in fatigue was studied and it was concluded that an increase in the surface layer stress decreases the fatigue. Prestraining of the specimen and removal of the surface layer is suggested as a practical method of increasing fatigue life. This method increases the fatigue life substantially. Author
- Metallurgy and Metallography