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Fatigue and Damage Tolerance Analysis of a Hybrid Composite Tapered FlexbeamThe behavior of nonlinear tapered composite flexbeams under combined axial tension and cyclic bending loading was studied using coupon test specimens and finite element (FE) analyses. The flexbeams used a hybrid material system of graphite/epoxy and glass/epoxy and had internal dropped plies, dropped in an overlapping stepwise pattern. Two material configurations, differing only in the use of glass or graphite plies in the continuous plies near the midplane, were studied. Test specimens were cut from a full-size helicopter tail-rotor flexbeam and were tested in a hydraulic load frame under combined constant axialtension load and transverse cyclic bending loads. The first determination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group in the tapered region of the flexbeam, near the thick end. Delaminations grew slowly and stably, toward the thick end of the flexbeam, at the interfaces above and below the dropped-ply region. A 2D finite element model of the flexbeam was developed. The model was analyzed using a geometrically non-linear analysis with both the ANSYS and ABAQUS FE codes. The global responses of each analysis agreed well with the test results. The ANSYS model was used to calculate strain energy release rates (G) for delaminations initiating at two different ply-ending locations. The results showed that delaminations were more inclined to grow at the locations where they were observed in the test specimens. Both ANSYS and ABAQUS were used to calculate G values associated with delamination initiating at the observed location but growing in different interfaces, either above or below the ply-ending group toward the thick end, or toward the thin end from the tip of the resin pocket. The different analysis codes generated the same trends and comparable peak values, within 5-11 % for each delamination path. Both codes showed that delamination toward the thick region was largely mode II, and toward the thin region was predominantly mode I. The calculated peak G-values from either analysis predict delamination is most likely to occur along the same interface where it was observed in the test specimens. Calculated peak G values were used with material characterization data to calculate a curve relating the fatigue life of the specimens, N, to the applied transverse load, V, for a given constant axial load.
Document ID
20010059024
Acquisition Source
Langley Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Murri, Gretchen B. (Army Research Lab. Hampton, VA United States)
Schaff, Jeffrey R. (United Technologies Research Center East Hartford, CT United States)
Dobyns, Al (Sikorsky Aircraft Stratford, CT United States)
Date Acquired
September 7, 2013
Publication Date
January 1, 2001
Subject Category
Composite Materials
Meeting Information
Meeting: American Helicopter Society Forum
Location: Washington, DC
Country: United States
Start Date: May 9, 2001
End Date: May 11, 2001
Sponsors: American Helicopter Society, Inc.
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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