Study of induced ultrasonic deviation for the detection and identification of ply waviness in carbon fibre reinforced polymer

Ply waviness is a major defect, which can appear in certain composite materials such as CFRP. Attenuation and ultrasound velocity measurements allow the detection, but not the identification, of ply waviness. In the present study it is shown that in order to identify this ply waviness, it is important to take the deviation of the ultrasonic beam into account. Two different methods allowing such deviations to be detected are proposed. On the one hand, the deviation produces an asymmetrical behaviour in the responses obtained at oblique incidence angles. This phenomenon is revealed through the study of incidence angle ranges, which can normally be superimposed. On the other hand, the double scanning technique allows the deviation of the energy maxima of the transmitted acoustic field to be determined. In both cases, the study of induced deviation reveals that it is sensitive to the presence of ply waviness. These methods have been experimentally validated and their potential use, depending on the thickness of the component, is discussed.