Nondestructive testing for bonding defects in aerospace composite based on continuous terahertz wave

This paper studies the applications of continuous terahertz wave in nondestructive testing for bonding defects in aerospace thermal insulation composite. Aerospace thermal insulation composite and metal substrates are bonded by epoxy resin adhesive as the experimental sample. The adhesive interface is tested by the reflection type frequency modulated continuous terahertz wave testing system and the frequency range is 0.23~0.32 THz. Tomographic images are obtained by making the terahertz probe focus on the adhesive interface. The size, shape and position of the defect can be judged by the gray value of images which at 0, 1 and 2 mm below the focal plane. In the imaging processing, edge detection is managed with adaptive threshold Canny operator. The adhesive interface between metal substrates and aerospace thermal insulation composite can be tested by applying the method of continuous terahertz imaging and combined with proper image detection technique.