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Characteristics of In-Plane Waves in Composite Plates

The high frequency dynamic excitations generate both in-plane as well as bending waves in structures. In aerospace applications, many of these structures are made of composite materials. There are two types of in-plane motions, longitudinal and in-plane shear. Although these motions are uncoupled in isotropic materials, composite structures show coupled behaviour. The works reported on in-plane waves in composite structures assume that two in-plane motions are uncoupled as in isotropic plates. In this work, characteristics of the in-plane waves in composite laminated plates are investigated. Expressions for wavenumber, phase speed and group speed are derived. It is seen that in composite plates the two in-plane waves are coupled in longitudinal and shear propagations and are non-dispersive. The phase speeds of in-plane waves in composite plates can be much different from those determined using the expressions for isotropic plates where the waves are uncoupled. To validate the expressions derived the phase speeds of in-plane waves in a typical composite panel are determined experimentally. It is seen that the experimentally obtained phase speeds match well with the theoretical results.