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Effects of a high mean stress on the high cycle fatigue life of PWA 1480 and correlation of data by linear elastic fracture mechanicsHigh-cycle fatigue tests using 5-mm-diameter smooth specimens were performed on the single crystal alloy PWA 1480 (001 axis) at 70F (room temperature) in air and at 100F (538C) in vacuum (10 to the -6 power torr). Tests were conducted at zero mean stress as well as at high tensile mean stress. The results indicate that, although a tensile mean stress, in general, reduces life, the reduction in fatigue strength, for a given mean stress at a life of one million cycles, is much less than what is predicted by the usual linear Goodman plot. Further, the material appears to be significantly more resistant to mean stress effects at 1000F than at 70F. Metallographic examinations of failed specimens indicate that failures in all cases are initiated from micropores of sizes of the order of 30 to 40 microns. Since the macroscopic stress-strain response in all cases was observed to be linear elastic, linear elastic fracture mechanics (LEFM) analyses were carried out to determine the crack growth curves of the material assuming that crack initiation from a micropore (a sub o = 40 microns) occurs very early in life. The results indicate that the calculated crack growth rates at an R (defined as the ratio between minimum stress to maximum stress) value of zero are approximately the same at 70F as at 1000F. However, the calculated crack growth rates at other R ratios, both positive and negative, tend to be higher at 70F than at 1000F. Calculated threshold effects at large R values tend to be independent of temperature in the temperature regime studied. They are relatively constant with increasing R ratio up to a value of about 0.6, beyond which the calculated threshold stress intensity factor range decreases rapidly with increasing R ratios.
Document ID
19860018217
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Majumdar, S. (Argonne National Lab. IL, United States)
Kwasny, R. (Argonne National Lab. IL, United States)
Date Acquired
September 5, 2013
Publication Date
November 1, 1985
Subject Category
Structural Mechanics
Report/Patent Number
NAS 1.26:175057
ANL-85-74
NASA-CR-175057
Accession Number
86N27689
Funding Number(s)
CONTRACT_GRANT: W-31-109-ENG-38
CONTRACT_GRANT: NASA ORDER C-91113-D
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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