Modal analysis of a Variable Stiffness Composite Laminated plate with diverse boundary conditions: Experiments and modelling

The modes of vibration of a Variable Stiffness Composite Laminate were obtained by experimental modal analysis and compared with the ones resulting from theoretical/mathematical models. Three types of boundary condition were considered: CFFF, CFCF and FFFF, where C stands for clamped and F for free edges. Frequency response functions were experimentally obtained and employed to identify natural frequencies, modal damping ratios and mode shapes of vibration, using methods known as CMIF - Peak picking and circle-fit. The identified natural frequencies and mode shapes of vibration were compared with the ones resulting from models based on Classical Plate Theory and on First-order Shear Deformation Theory. Although two massive, stiff, steel blocks were bolted with the plate in-between in order to approach a clamped boundary, the modal properties are still significantly influenced by the flexibility of the resulting fixture. After introducing springs along the boundaries in the mathematical model, to better represent a real clamped boundary, quite good agreement between theoretical and experimental results was obtained. The experimental results here presented can be used to validate theoretical models of Variable Stiffness Composite Laminated plates.