Evaluation of size of surface and subsurface waviness in carbon fiber composites using eddy current testing: a numerical study

An eddy current method to evaluate size of waviness in carbon fiber reinforced plastics is studied. It is shown that the shape of the waviness appears as a deformation of the magnetic field distribution. Finite element method analyses are performed to investigate relationships between the size of the waviness and that of the magnetic field deformation. The waviness length can be accurately estimated from the length of the magnetic field deformation. It is found that the amplitude of the magnetic field deformation decreases with waviness depth in a certain proportion that is independent of the waviness amplitude. Using these characteristics, the range of the waviness amplitude is obtained. The effect of waviness in multiple layers on waviness size evaluation is also investigated. It is revealed that multiple waviness causes either overestimation or underestimation of the upper limit of the waviness amplitude depending on the directions of constituent waviness.