Detection of skin desoldering defect in Ti-alloy honeycomb using linear frequency modulated infrared imaging

Ti-alloy honeycomb with variable skin thickness has been widely used in the aerospace field. Skin desoldering is one of the most common defects of Ti-alloy honeycomb sandwich. Because of single frequency, traditional lock-in thermography cannot defect desoldering under skin with a variety of thicknesses in one time and has low detection efficiency. To solve this problem, linear frequency modulated infrared imaging and excitation parameter selection method were studied. The finite element simulation model of Ti-alloy honeycomb was established by using ANSYS. Phase difference between desoldering region and normal region was calculated through correlation algorithm and the relationship between freqnency bandwidth, chirp time, skin thickness and maximum of phase difference absolute value was analyzed. Honeycomb sample with prefabricated desoldering defects was experimentally studied using linear frequency modulated exciting. Phase diagrams with different frequency bandwidth and different chirp time are obtained. The results show that one-time detection of Ti-alloy honeycomb with skin thickness 0.6-1.2 mm can be realized using linear frequency modulated signal with the frequency range 0.01-0.21 Hz and chirp time 22 s. These results provide a technical guidance for the practical detection of Ti-alloy honeycomb sandwich structure.