Anisotropy Influence on Guided Wave Propagation and Steering in Unidirectional CFRP

Carbon fiber reinforced composite laminates (CFRP) are often selected for aerospace structures due to their low weight and high strength compared to their metallic counterparts. They consist of very stiff and highly anisotropic fiber matrix ply layers, resulting in high in-plane strength. However, composite laminates are prone to barely visible impact damage when subjected to low velocity impacts during service. Undetected impact damage can cause significant strength reduction of the laminate. Effective structural health monitoring (SHM) of composite panels is therefore required to prevent component failure, which can be achieved using guided waves propagating along the structure. A number of guided wave propagation effects occur in composite laminates due to the high material anisotropy of the ply layers, such as directionality of phase and group velocity and wave steering effects. If unaccounted for, these anisotropic effects could lead to inaccurate localization of damage, and potential regions of the structure where guided waves do not provide sufficient defect detection sensitivity. Propagation of the A0 Lamb mode was investigated for multiple incident wave directions in an undamaged unidirectional CFRP panel. Full 3D Finite Element (FE) models were developed using homogenized anisotropic material properties to investigate the directional dependency of velocity. Non-contact guided wave velocity measurements were obtained using a laser vibrometer to validate the FE model. Both a point and line source were modelled to investigate the influence of the excitation source on the guided wave evaluation and signal processing. Significant wave skewing behavior was predicted from the numerical simulations for several wave propagation directions, with good agreement with theoretical values.