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An Evaluation of the Plasticity-Induced Crack-Closure Concept and Measurement Methods

Author:
Newman, James C., Jr.
Published:
Aug. 1998.
Physical Description:
1 electronic document
Online Version

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Summary:
An assessment of the plasticity-induced crack-closure concept is made, in light of some of the questions that have been raised on the validity of the concept, and the assumptions that have been made concerning crack-dp damage below the crack-opening stress. The impact of using other crack-tip parameters, such as the cyclic crack-tip displacement, to model crack-growth rate behavior was studied. Crack-growth simulations, using a crack-closure model, showed a close relation between traditional Delta K eff, and the cyclic crack-tip displacement (Delta eff) for an aluminum alloy and a steel. Evaluations of the cyclic hysteresis energy demonstrated that the cyclic plastic damage below the crack-opening stress was negligible in the Paris crack-growth regime. Some of the standard and newly proposed remote measurement methods to determine the 'effective' crack-tip driving parameter were evaluated on middle-crack tension specimens. A potential source of the Kmax effect on crack-growth rates was studied on an aluminum alloy. Results showed that the ratio of Kmax to Kc had a strong effect on crack-growth rates at high stress ratios and at low stress ratios for very high stress levels. The crack-closure concept and the traditional crack-growth rate equations were able to correlate and predict crack-growth rates under these extreme conditions.
Other Subject(s):
Collection:
NASA Technical Reports Server (NTRS) Collection.
Note:
Document ID: 19980234244.
NASA/TM-1998-208430.
NAS 1.15:208430.
L-17748.
Advances in Crack Closure Measurement and Analysis; 13-14 Nov. 1997; San Diego, CA; United States.
Terms of Use and Reproduction:
No Copyright.
View MARC record | catkey: 15644099