Polymeric composites are used to manufacture hingeless, bearingless composite rotor hubs for helicopters. These components are made of fewer parts and offer the advantages of reduced weight and drag, compared to metal hubs. During flight, these rotor hubs experience constant axial tension load from the centrifugal forces, and transverse bending in the flapping flexure region. In order to accommodate bending loads, composite flexbeams use internal ply-drops to create a nonlinear taper. In this study, nonlinear-tapered flexbeam specimens from a full-size composite helicopter rotor hub flexbeam were tested under combined constant axial tension and cyclic bending loads. Two different graphite/glass hybrid configurations tested under cyclic loading failed by delamination in the tapered region. A 2-D finite element model was developed which closely approximated the flexbeam geometry, boundary conditions, and loading. The analysis results from two geometrically nonlinear finite element codes, ANSYS and ABAQUS, are presented and compared. Strain energy release rates (G) associated with simulated delamination growth in the flexbeams are presented from both codes. These results compare well with each other and suggest that the initial delamination growth from the tip of the ply-drop toward the thick region of the flexbeam is strongly mode II. The peak calculated G values were used with material characterization data to calculate fatigue life curves for comparison with test data. A curve relating maximum surface strain to number of loading cycles at delamination onset compared well with the test results.
Fatigue life methodology for tapered hybrid composite flexbeams
Composites Science and Technology ; 66 , 3-4 ; 499-508
2006
10 Seiten
Article (Journal)
English
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