Enhanced structural behavior of flexible laminated composite beams

The aim of the present study is to investigate analytically and numerically the structural behavior of laminated composite beams under axial compression using piezoelectric layers. A mathematical model was developed based on a first order shear deformation theory (FSDT) which includes shear deformations, usually neglected in the classical lamination theory of composite structures. Closed form solutions for the bending angle and the axial and lateral displacements along the beam are presented for various boundary conditions. Natural frequencies and their associated mode shapes, as well as, buckling loads were computed for beams with and without piezoelectric layers influence, having various boundary conditions and lay-ups. Next, the influence of the piezoelectric layers on the axial compression load and the natural frequencies is investigated to yield an enhancement of the structural behavior of the beam. This is done using a proportional control load, in which the sensed voltage on the beam is fed back (after being amplified using a constant gain G), onto the PZT actuators which prevent the premature buckling of the flexible beam by actively increasing its stiffness. A parametric investigation was performed for beams with various lay-ups, and it was shown that for a given feedback gain value, the natural frequencies and the buckling loads can be increased by a factor of two, when using the enhancement procedure developed within the present study.