Hybrid Thermographic Detection of Kissing Unbond Defects

Fast, portable IR NDE systems capable of automated operation and quantitative defect measurement are now commercially available, and have been credited with significant cost savings in aerospace manufacturing and service sectors. However, despite advantages of speed and wide area, non-contact inspection, IR methods are limited in their ability to detect disbonds in which there is mechanical contact but no adhesive bond. We will investigate the feasibility of a system for detection of these ¿kissing unbonds¿ using a novel combination of pulsed thermography and applied vacuum stress. Both vacuum stress and flash heating will be applied to the part, and a differential IR image comparing the post-flash cooling of the stressed and unstressed part will be generated. The apparatus for acquiring the image and applying the heating and vacuum stress will be housed in a portable hood with a 10¿ x 10¿ field of view, and typical acquisition times of 20 seconds. If successful, the fully realized system will extend the capabilities of thermographic NDE systems to allow inspection of skin to core disbonds in honeycomb and foam core structures, and thick composite components used in the space shuttle and X-33, as well as commercial and military aircraft.