Actions for Investigation of Cracks Found in Helicopter Longerons

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Investigation of Cracks Found in Helicopter Longerons

Author
Newman, John A.
Published
July 15, 2009.
Physical Description
1 electronic document
Additional Creators
Wallace, Terryl A. and Baughman, James M.
Online Version

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Summary
Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurigical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.
Other Subject(s)
Collection
NASA Technical Reports Server (NTRS) Collection.
Note
Document ID: 20100011385.
LF99-9172.
Terms of Use and Reproduction
Copyright, Distribution as joint owner in the copyright.
View MARC record | catkey: 15995682