Energy dissipation during vibrations of non-uniform composite structures. 3. Numerical experiments

Abstract

The influence of the relative thickness of the “stiff” viscoelastic layer polymer and the orientation of the reinforcing layers of the power layer on the values of their natural frequencies and loss factors of damped oscillations unsupported two-layered composite plate is investigated. It has been established that each natural vibration mode of two-layered plate corresponds to a certain effective relative thickness of isotropic viscoelastic polymer layer. Further increase in relative thickness for plates with orthotropic or transversally isotropic bearing layer depending on ambient temperature may result in both growth and decrease of natural frequencies without any considerable change of their energy dissipation. For the plates with monoclinic bearing layer, increase in relative thickness of isotropic viscoelastic polymer layer is accompanied by both decrease and increase of loss factor for different vibration modes because these structure have membrane-bending-shearing interaction that results in the change of natural vibration shapes. It is shown that change in stacking sequence of reinforcing layers in the bearing layer with respect to global axes of two-layered plate brings about mutual transformation domains of coupled vibration modes. It has been established that mutual transformation of natural coupled vibration mode shapes of unsupported quasi-uniform rectangular plate appears in case if at least in one of the plate directions one of the natural shapes has an even number of quarter-wavelengths, whereas another natural shape has odd. It has been demonstrated that temperature-frequency relationship of elastic-dissipative characteristics of the “stiff” viscoelastic polymer has a considerable effect upon natural frequencies and loss factors of all the investigated vibration modes for unsupported rectangular two-layered plate.