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Small-crack effects in high-strength aluminum alloysThe National Aeronautics and Space Administration and the Chinese Aeronautical Establishment participated in a Fatigue and Fracture Mechanics Cooperative Program. The program objectives were to identify and characterize crack initiation and growth of small cracks (10 microns to 2 mm long) in commonly used US and PRC aluminum alloys, to improve fracture mechanics analyses of surface- and corner-crack configurations, and to develop improved life-prediction methods. Fatigue and small-crack tests were performed on single-edgenotch tension (SENT) specimens and large-crack tests were conducted on center-crack tension specimens for constant-amplitude (stress ratios of -1, 0, and 0.5) and Mini-TWIST spectrum loading. The plastic replica method was used to monitor the initiation and growth of small fatigue cracks at the semicircular notch. Crack growth results from each laboratory on 7075-T6 bare and LC9cs clad aluminum alloys agreed well and showed that fatigue life was mostly crack propagation from a material defect (inclusion particles or void) or from the cladding layer. Finite-element and weight-function methods were used to determine stress intensity factors for surface and corner cracks in the SENT specimens. Equations were then developed and used in a crack growth and crack-closure model to correlate small- and large-crack data and to make life predictions for various load histories. The cooperative program produced useful experimental data and efficient analysis methods for improving life predictions. The results should ultimately improve aircraft structural reliability and safety.
Document ID
19940029793
Acquisition Source
Legacy CDMS
Document Type
Other - NASA Reference Publication (RP)
Authors
Newman, J. C., Jr. (NASA Langley Research Center Hampton, VA, United States)
Wu, X. R. (NASA Langley Research Center Hampton, VA, United States)
Venneri, S. L. (NASA Langley Research Center Hampton, VA, United States)
Li, C. G. (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
September 6, 2013
Publication Date
May 1, 1994
Subject Category
Structural Mechanics
Report/Patent Number
NASA-RP-1309
L-17244
NAS 1.61:1309
Accession Number
94N34299
Funding Number(s)
PROJECT: RTOP 505-63-50-04
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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