3. Bending-Torsional Piezoactuation.
3 (a) Study of Open-Section Beams Actuated by Skewed Piezoelements.
The objective of this prortion
of the project is to gain a detailed insight into the behavior of an open-section
beam actuated by sparsely distributed skewed piezoelements. We have shown
that significant changes in torsional and bending displacements occur along
non-actuated portions of the beam (e.g., between piezoactuators or between
a piezoactuator and the tip of the beam). Those displacements have to be
accounted for in theoretical models of such structures. Fig. 1 shows a
typical specimen used for validating the developed theory. Fig. 2 shows
a comparison between experimental results and results obtained using theories
accounting for and neglecting the displacements along not actuated portions
of the beam.
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| Fig. 1 Composite beam actuated by skewed piezoelements on a test stand. | Fig. 2 Tip bending slope for a beam actuated by skewed piezoelements with aspect ratio of 3.7. |
3 (b) Damping of Bending-Torsional Vibrations in Closed-Section Beams.
This portion of the project investigates the feasibility of applying piezoactuators to damp vibrations of closed cross-section composite beams. We tested two specimens: a 60 mm x 60 mm x 600 mm beam shown in Fig. 3, and a 55 mm x 15 mm x 600 mm beam shown in Fig. 5, where 1 represents a composite shell, and 2 indicates piezoactuators. The square cross-section beam was too stiff in bending to produce any meaningful results. Damping coefficient of torsional vibrations was increased from 0.012 to 0.1 by the activation of the piezoactuator. A sample time history showing the performance of the piezoactuator in damping torsional vibrations is shown in Fig. 4. Fig. 6 shows a sample time history demonstrating the performance of piezoelements bonded to the walls of the rectangular cross-section beam in damping bending vibrations. The piezoelectric actuator increased the magnitude of damping coefficient from z = 0.015 to z = 0.036 for bending vibrations. However, there was practically no improvement in torsional vibrations damping. We are currently working on correcting that problem.
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| Fig. 5 Closed cross-section piezobeam. | Fig. 6 Bending vibrations damping. |
For details, see:
Kawiecki, G., 1998, "Finite Element Study of Open-section Beams Actuated by Skewed Piezoelements," Smart Materials and Structures Journal, Vol. 7, No. 1, February, pp. 85-94.
Kawiecki, G., Smith, W. P.
and Hu, C., 1995, "Feasibility Study of a Torsional-Bending Piezoelectric
Actuator," Journal of Intelligent Material Systems and Structures,
Vol. 6, No. 4, July, pp. 465-473 .
Students involved in this project: James Hu, Lumin Jiang, Stephen Jesse, Tony Jopling, Winthrop Smith.
Sponsored by the National Science Foundation under grant CMS-9402802.