Torsional Buckling Analysis and Damage Tolerance of Graphite/Epoxy Shafts

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Abstract
The measured torsional buckling load of Graphite/Epoxy shafts is found in good agree ment with theoretical predictions based on a general shell theory that includes elastic cou pling effects and transverse shearing deformations. The direction of the applied torque and the lay-up stacking sequence drastically affects the buckling load (up to 80%). Transverse shearing deformations are found significant when the number of circumferential waves in the buckling pattern is larger than 3. The residual strength of shafts with holes is also measured, and the dominant failure mode remains torsional buckling. The buckling mode patterns are seemingly unaffected by damage but buckling loads are lower compared to un damaged specimens. Material failure concentrated around the hole does not occur until the hole size is approximately one-third of the shaft's diameter. Teflon disks inserted between plies to simulate delaminations decrease the buckling load, but not significantly. In con clusion, stiffness characteristics, rather than strength characteristics dominate the behavior of thin-walled, undamaged shafts under torsional load, and this appears to remain true for shafts with sizable damage (up to about one-third of the shaft's diameter).