Detection of skin desoldering defect in Ti-alloy honeycomb structure using lock-in infrared thermography test

Skin desoldering is the most common defect of Ti-alloy honeycomb sandwich during manufacturing and serving period. Due to low thermal conductivity of Ti-alloy material, as the skin of Ti-alloy honeycomb sandwich becomes thicker, temperature signal difference of defect and non-defect becomes weaker, and thus it is more difficult to test the defect by infrared thermography. Given the problem, the range of modulation frequency in this structure with different skin thickness by lock-in infrared thermography was studied. The finite element simulation model was built to analyze the variation of surface temperature under the heat flow. The extracted phase differences of defect and non-defect area based on correlation algorithm are available to analyze the effect of modulation frequency and skin thickness on these phase differences. Experiments were performed on the specimen with prefabricated defects of this structure using lock-in infrared detection system. The relationship between the phase difference and the modulation frequency was given after extracting the phase of defect and non-defect area. The research results show that the 0.04-0.10 Hz modulation frequencies applied to detect this structure of skin thickness within 0.6-2.0 mm can get optimal results. Research results provide a technical guidance for the practical detection of Ti-alloy honeycomb sandwich structure.