Evaluation of Anisotropic Properties of Graphite-Epoxy Composites Using Lamb Waves

Abstract

While most measurements previously were made on bulk samples, composite materials are often produced in the form of thin sheets ("skin"). For this type of material, the most important property is the in-plane elasto-aniso- tropic characteristic. To measure this, Lamb waves are fairly adequate. Thompson et al. [8] used low frequency flexural waves (A0 Lamb mode) in the direction of the axis of symmetry for study of honeycomb sandwich panels. For estimation of the stiffness of thin composite plates, it is reasonably adequate to use the low frequency S0 Lamb mode (plate mode). In this paper, the polar characteristics for phase and group velocities of the low frequency S0 Lamb mode were studied in unidirectional, two- directional, and quasi-isotropic graphite-epoxy composite panels. The results of the experimenta were compared with theoretical calculations. The main attention is given to the description of the measurement concepts. EXPERIMENTAL