This paper describes the physics of the interaction of the eddy current probe and the delamination in multidirectional carbon fiber reinforced polymer (CFDR). Currently, there is an opinion that eddy current signals obtained due to delamination in multidirectional CFRP are caused by the redistribution of the vertical eddy current arising from the excitation of eddy currents in the sample by a rectangular coil whose surface is orthogonal to the surface of the sample. The analysis performed by us shows that the possibility of creation and deformation of the vertical eddy current is very questionable, and that the observed eddy current signals associated with the delamination are most likely caused by carbon fiber plies misalignment towards the sample surface. In this paper was compare eddy-current signals from the delamination in CFRP in samples where the existence of vertical eddy current is possible in theory and in samples where this is not possible. The obtained signals had similar measurements, and this indirectly indicates the doubtfulness of the hypothesis of the delamination detection in CFRP samples due to vertical eddy current.

The paper is concerned with increasing sensitivity of eddy current nondestructive testing of most dangerous delamination in carbon-fiber reinforced plastics (CFRP). Increased sensitivity is achieved by separate registration and comparison of eddy current signals obtained from a set of stratifications of carbon fibers with the same orientation. The separation of eddy current signals is possible due to pronounced anisotropy of the electrical conductivity of the layers dominant in the direction of the fibers of the corresponding layer. Eddy-current signals are registered by eddy current probes with maximum sensitivity in a given angular direction. Prior to the scan eddy current signals of the probe are leveled on a defect-free area. The influence of the working gap on the difference between the eddy current signals of the probe is suppressed by normalizing it according to one of the signals. The analysis of the registered signals from delamination has been performed using an approximate calculation model. The reliability of the obtained results has been confirmed by comparison with experimental results and calculations using the finite element method.