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Mean stress and the exhaustion of fatigue-damage resistanceMean-stress effects on fatigue life are critical in isothermal and thermomechanically loaded materials and composites. Unfortunately, existing mean-stress life-prediction methods do not incorporate physical fatigue damage mechanisms. An objective is to examine the relation between mean-stress induced damage (as measured by acoustic emission) and existing life-prediction methods. Acoustic emission instrumentation has indicated that, as with static yielding, fatigue damage results from dislocation buildup and motion until dislocation saturation is reached, after which void formation and coalescence predominate. Correlation of damage processes with similar mechanisms under monotonic loading led to a reinterpretation of Goodman diagrams for 40 alloys and a modification of Morrow's formulation for life prediction under mean stresses. Further testing, using acoustic emission to monitor dislocation dynamics, can generate data for developing a more general model for fatigue under mean stress.
Document ID
19900004503
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Berkovits, Avraham
(NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 6, 2013
Publication Date
November 1, 1989
Subject Category
Structural Mechanics
Report/Patent Number
NASA-TM-101311
NAS 1.15:101311
E-4307
Accession Number
90N13819
Funding Number(s)
PROJECT: RTOP 582-01-11
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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