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Fatigue crack growth in 7475-T651 aluminum alloy plate in hard vacuum and water vaporCompact specimens of 25 mm thick aluminum alloy plate were subjected to constant amplitude fatigue testing at a load ratio of 0.2. Crack growth rates were determined at frequencies of 1 Hz and 10 Hz in hard vacuum and laboratory air, and in mixtures of water vapor and nitrogen at water vapor partial pressures ranging from 94 Pa to 3.8 kPa. A significant effect of water vapor on fatigue crack growth rates was observed at the lowest water vapor pressure tested. Crack rates changed little for pressures up to 1.03 kPa, but abruptly accelerated at higher pressures. At low stress intensity factor ranges, cracking rates at the lowest and highest water vapor pressure tested were, respectively, two and five times higher than rates in vacuum. Although a frequency was observed in laboratory air, cracking rates in water vapor and vacuum are insensitive to a ten-fold change in frequency. Surfaces of specimens tested in water vapor and vacuum exhibited different amounts of residual deformation. Reduced deformation on the fracture surfaces of the specimens tested in water vapor suggests embrittlement of the plastic zone ahead of the crack tip as a result of environmental interaction.
Document ID
19820015429
Acquisition Source
Legacy CDMS
Document Type
Thesis/Dissertation
Authors
Dicus, D. L. (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
September 4, 2013
Publication Date
November 1, 1981
Subject Category
Metallic Materials
Report/Patent Number
NAS 1.15:84193
NASA-TM-84193
Accession Number
82N23303
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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