Axial Stiffness Variation of Thin Walled Laminated Composite Beams Using Piezoelectric Patches- a New Experimental Insight

Altering the natural frequencies of slender thin walled laminated composite beams by changing its stiffness has been reported in the literature. This had been performed either using optimal mechanical and thermal induced stresses or using collocated piezoelectric patches bonded on the structure. It was shown that for the cases of a beam equipped with piezoelectric patches, restraining the beam's axial displacements at its two ends can lead to either softening or stiffening of the beam stiffness, as a function of the voltage supplied to the patches. However, when those structures behave like a cantilevered beam, or a free-free beam, classical beam theories show that the lateral vibrations of those beams cannot be altered by applying a constant electric voltage to the collocated surface bonded piezoelectric layers or patches. This occurs because the resultant force on each cross section of the beam is always identically zero (due to the fact that no axial external forces are applied on the beam). It is the aim of the present manuscript to show that under certain circumstances one can alter also the natural frequencies of a cantilevered piezo laminated beam. The present paper will investigate this phenomenon, and provide a new insight into this topic.