Abstract
This study focused on non-destructive inspection of CFRPs using induction-heating thermography. To enhance the defect detectability, phase images constructed by Fourier transformation from conventional thermal images were used. The temperature images obtained using a CFRP specimen with artificial delamination included strong non-uniform temperature distribution caused by non-uniform heating by induction coil, and this distribution significantly disturbed the images of the inside defects. On the other hand, in the phase images, the influence of non-uniform heating was suppressed at certain frequencies, and the defects that could not be detected in the temperature images were detected. Analytical studies revealed that the phase at a location in the non-uniformly heated region periodically oscillated with a period that is reciprocal of the heating duration when the phase were calculated from the temperature data including both heating and cooling stages. Owing to this oscillation, phase contrast between the regions heated and unheated by the induction coils was periodically decreased, which means that the effect of non-uniform heating was periodically suppressed and that defects can be easier detected in the phase images.
