Modal Analysis for Impact of Layered Plates

An analysis is presented of the plane strain response of an arbitrarily layered elastic plate to surface impact loads of specified distribution over the plate surface and in time. Each layer has specified orthotropic material properties, with coincident material and plate axes. The method is based on the extended Ritz technique and employs a normal mode procedure to accurately predict the motion through the plate thickness of stress waves generated by the impact load. The case of impact on an isotropic plate is studied in detail, both with the present method and other methods based on the exact elasticity theory to indicate the accuracy and convergence properties of this method. The procedure is applied to the case of a two-layer plate, where each layer is assigned orthotropic elastic properties typical of a unidirectional boron-epoxy composite. The stress waves generated by a normal surface impact are presented to indicate both the quality and quantity of information that can be generated by the analysis. A tension wave that trails the initial compression wave is shown to exist.