Application of lock-in thermography for the inspection of disbonds in titanium alloy honeycomb sandwich structure

This paper investigates the lock-in thermography testing of skin-to-core disbonds in titanium alloy honeycomb structure. A three-dimensional finite element model of titanium alloy honeycomb sandwich structure is built. The phase difference between the disbond defect region and the nondefective region is used to optimize the excitation frequency. The phase variation of the surface temperature because of the discontinuity of the honeycomb structure is analyzed. And the relationship between the phase difference of the defect and the nondefective region and the thickness of the disbond is obtained. Two titanium alloy honeycomb sandwich structure specimens with skin-to-core disbond defects were manufactured. Different from the conventional method of simulating disbond defects, two methods of prefabricating intimate contact disbond are proposed to form real defects. The lock-in thermography experiments are carried out on the specimens. The digital correlation method is used to process the infrared image sequence. The experimental results show that lock-in thermography is effective in inspecting the intimate contact disbond in titanium alloy honeycomb sandwich structure.