The effect of microstructure and environment on fatigue crack closure of 7475 aluminum alloy
The effects of slip character and grain size on the intrinsic material and extrinsic closure contributions to fatigue crack growth resistance have been studied for a 7475 aluminum alloy. The alloy was tested in the underaged and overaged conditions with grain sizes of 18 and 80 . The fracture surface exhibited increased irregularity and planar facet formation with increased grainsize, underaging, and tests in vacuum. These changes were accompanied by an increased resistance to fatigue crack growth In air the 18 grain size overaged material exhibited relatively poor resistance to fatigue crack growth compared with other microstructural variants, and this was associated with a lower stress intensity for closure. All materials exhibited a marked improvement in fatigue crack growth resistance when tested in vacuum, with the most significant difference being about 1000 X at a K of 10 MPa m /SUP 1/2/ for the 80 grain size underaged alloy. This improvement could not be accounted for by either an increase in closure or increased crack deflection and is most likely due to increased slip reversibility in the vacuum environment. The intrinsic resistance of the alloy to fatigue crack growth was microstructurally dependent in vacuum, with large grains and planar slip providing the better fatigue performance.
- Research Organization:
- U.S. Army Corps of Engineers, Tulsa, OK
- OSTI ID:
- 6199299
- Journal Information:
- Metall. Trans., A; (United States), Journal Name: Metall. Trans., A; (United States) Vol. 15A:3; ISSN MTTAB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
CRACK PROPAGATION
CRYSTAL STRUCTURE
DESTRUCTIVE TESTING
FATIGUE
FRACTURE MECHANICS
FRACTURE PROPERTIES
GRAIN SIZE
MATERIALS TESTING
MECHANICAL PROPERTIES
MECHANICS
MICROSTRUCTURE
PRESSURE EFFECTS
SIZE
SLIP
STRESS INTENSITY FACTORS
TESTING