Dynamic behaviour of metallic and composite plates under in-plane loads

The dynamic behaviour of plates under compressive in-plane static loads will be examined in the present paper. From an analytical point of view the effects of forces acting in the undeformed middle surface of plates on the bending natural frequencies and mode shapes are well known. For a simple plate as the compressive edge force approaches to the buckling value the first natural frequency tends to zero. Nevertheless the experimental assessment is complex as the middle plane of the plate does not remain plane up to the critical compressive load, owing to the initial imperfections of the plate and misalignment of load. The dynamic behaviour, in fact, is strongly sensitive to the change of the middle plane curvature. Measured natural frequencies and, in same case, also mode shapes are quite different from the predicted theoretical values when curvatures become not negligible. In the paper is shown that anyway it is possible to predict with a good accuracy the buckling load. Using a limited number of measured natural frequencies at various compressive loads, the buckling load is achievable extrapolating these values. This procedure has been applied for an aluminum alloy plate for two edge constraint conditions. Tests on composite plates under compressive and shear load are going to be performed in order to assess the procedure for a more general case.