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On the use of marker loads and replicas for measuring growth rates for small cracksThe initiation and growth of small cracks (5-500 microns m) from edge notches in 2024-T3 aluminum alloy sheets were studied under constant amplitude loading. Two methods were used to measure crack shape and size. In the first method, striation marker bands were periodically formed along the crack front by interrupting the constant amplitude loading by either an elevated R-ratio load sequence, or by an overload sequence. In the second method, the surface crack length was monitored by taking surface replicas at regular intervals. The marker band techniques did not provide reliable crack length and crack shape information for cracks smaller than 2 mm. The replica technique provided accurate information for surface crack length at all crack lengths, and fracture tests on specimens with small cracks provided crack-shape information. Crack growth rates were plotted against the stress intensity factor ranges. The results exhibited the small crack effect, in that the small cracks grew faster than large cracks at the same stress-intensity factor range. A crack closure model was also used to analyze the growth of small cracks from small (inclusion) defects at the notch surface.
Document ID
19850016020
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Swain, M. H.
(NASA Langley Research Center Hampton, VA, United States)
Newman, J. C., Jr.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 12, 2013
Publication Date
November 1, 1984
Publication Information
Publication: AGARD Fatigue Crack Topography
Subject Category
Structural Mechanics
Accession Number
85N24331
Distribution Limits
Public
Copyright
Other
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