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Effects of constraint on crack growth under aircraft spectrum loadingThe objective is to study the effects of constraint on fatigue crack growth under aircraft spectrum loading. A plasticity-induced crack-closure model that accounts for constraint variations during the transition from flat-to-slant crack growth was used to correlate crack-growth rate data under constant-amplitude loading and to calculate crack growth under simulated aircraft spectrum loading. The model was applied to several thin-sheet aluminum alloy materials. Under laboratory air conditions, the transition was shown to be related to the size of the cyclic plastic zone based on the effective stress-intensity factor range for several sheet materials and thicknesses. Results from three-dimensional, elastic-plastic, finite-element analyses of a flat, straight-through crack in a thin-sheet aluminum alloy specimen showed a constraint loss similar to that assumed in the model. Using test data and the closure model, the location of the constraint-loss regime in terms of growth rate and the value of the constraint factor at these rates were determined by trial and error. The model was then used to calculate crack growth under the TWIST spectrum. The calculated results agreed reasonably well with test data. In general, the model predicted shorter crack-growth lives than tests under the TWIST spectrum by about 40 percent. For the TWIST spectrum clipped at Level 3, the calculated lives were within about 20 percent. The results demonstrated that constraint variations, especially for thin-sheet alloys, should be accounted for to predict crack growth under typical aircraft spectra.
Document ID
19920024934
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Newman, J. C., Jr.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
September 6, 2013
Publication Date
September 1, 1992
Subject Category
Structural Mechanics
Report/Patent Number
NASA-TM-107677
NAS 1.15:107677
Report Number: NASA-TM-107677
Report Number: NAS 1.15:107677
Accession Number
92N34178
Funding Number(s)
PROJECT: RTOP 538-02-10-01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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