Inspection of disbonds in titanium alloy honeycomb sandwich structures with different skin thicknesses using linear frequency-modulated thermography

This paper reports the linear frequency-modulated thermography inspection of disbonds in titanium alloy honeycomb sandwich structures with different skin thicknesses. A three-dimensional finite element model of a titanium alloy honeycomb sandwich structure is built. The maximum value of the phase difference between the disbond defect region and the nondefective region is used to optimize the heating duration and frequency bandwidth. Three titanium alloy honeycomb sandwich structure specimens, with a skin thickness of 0.6 mm, 0.85 mm, and 1.2 mm, respectively, are manufactured, in which skin-to-core disbond defects are prepared. The linear frequency-modulated thermography experiments are carried out on the specimens. The correlation algorithm is used to process the infrared image sequences. The experimental results show that linear frequency-modulated thermography can realize the fast and efficient inspection of the disbonds in titanium alloy honeycomb sandwich structures with different skin thicknesses. For skin thickness ranges from 0.6 mm to 1.2 mm, a heating duration of 22 s and a frequency range of 0.01 Hz-0.21 Hz are recommended.