Free vibration analysis of laminates with circular cutout by hybrid-stress finite element

The natural frequencies of laminated composite plates with central circular cutout were analyzed using a hybrid-stress finite element and a specially developed computer program. The four lowest natural frequencies of the laminate were evaluated by varying the fiber orientation, the width-to-thickness ratio, the aspect ratio, and the hole size. It was found that, in the case of thick symmetric or antisymmetric laminates, all four natural frequencies increased with the fiber angle theta up to about 45 deg. In the case of a thin laminate, the first and the fourth natural frequencies showed a similar tendency, while the third frequency increased with theta up to about 20 deg. Variations in the fiber orientation caused only marginal variations in the third (beyond 20 deg) and the second frequencies.