Effect of multiple delaminations on free vibration characteristic for composite laminates

Based on the first-order shear deformation theory of the composite laminated plate, an FEA model and the method of free vibration analysis for the composite laminates with multiple through-width delaminations were developed, and a linearity contact model was established to simulate the interaction between upper and lower sub-laminates along the delaminated region during the vibration process. The effects of the location and numbers of delamination, and boundary condition of the laminates on the vibration characteristic were discussed. From some typical examples, the results show that, with the variation of delamination location along the length direction, the influence of inner delaminations on frequencies is greater than that of the surface delaminations, but both variation trends are approximate. With the delaminations nearer to the middle plane along the thickness direction, the influence is more severe. When the delaminations are near to the surface and the edges constraints of the laminates are weak, the vibration analysis for the multiple delaminations case can be simplified into that for the one delamination case.