Using differential spread laser infrared thermography to detect delamination and impact damage in CFRP

In this paper, the feasibility of differential spread laser infrared thermography (DSLIT) to detect delamination and impact damage in carbon fiber reinforced polymer (CFRP) is investigated. The proposed method can significantly eliminate the influence of the uneven laser energy distribution and improve the detectability of laser infrared thermography. First, numerical simulation is carried out following the procedure of DSLIT to verify the feasibility of this method. Secondly, through experiments on the detection of defects both in practical aviation CFRP and common CFRP, the feasibility of DSLIT is confirmed. For the common CFRP, this technique has excellent performance: a defect at a depth of 2.5 mm was detected successfully, with the width-to-depth ratio reaches to 2.4. Comparatively speaking, the defect detection results for the aviation CFRP are not as good as those for the common CFRP. However, defects at a depth of 1.125 mm were detected, with the width-to-depth ratio reaching 2.67. In addition, defects caused by a low-velocity impact in practical aviation CFRP were successfully detected. Finally, the thermal data were processed by image processing methods such as sequence differential preprocessing (SDP), phase analysis (PA) and principal component analysis (PCA) to enhance the defect imaging results.